Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Taylor & Francis  

Optical birefringence imaging techniques have enabled quantitative evaluation of macroscopic structures, e.g. domains and grain boundaries. With inhomogeneous samples, the selection of regions for analysis can significantly affect the conclusions; thus, arbitrary selection can lead to inaccurate findings. Thus, in this study, we present a method to cluster all birefringence imaging data using -means multivariate clustering on a pixel-by-pixel basis to eliminate arbitrariness in the region selection process. Linear statistics cannot be applied to the polarization states of light described by angles and their periodicity; thus, circular statistics are used for clustering. By applying this approach to a 42,280-pixel image comprising 12 explanatory variables of stress-induced ferroelectricity in SrTiO3, we were able to select a region of locally developed spontaneous polarization. This region covers only 1.9% of the total area, where the stress and/or strain is concentrated, thereby resulting in a higher ferroelectric phase transition temperature and larger spontaneous polarization than in the other regions. The -means multivariate clustering with circular statistics is shown to be a powerful tool to eliminate arbitrariness. The proposed method is a significant analysis technique that can be applied to images using the polarization of light, azimuthal angle of crystals, scattering angle.

DOI： 10.1080/27660400.2023.2278322

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/PhysRevB.107.184405

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Other Link： https://link.aps.org/article/10.1103/PhysRevB.107.184405

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Journal of the Physical Society of Japan  

DOI： 10.7566/JPSCP.38.011112

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Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Journal of the Physical Society of Japan  

DOI： 10.7566/JPSCP.38.011142

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

The two-dimensional Heisenberg antiferromagnet (C2H5NH3)2CuCl4 has attracted attention as a good candidate for a type I multiferroic compound. In contrast to magnetism, however, the mechanism of ferroelectricity has not been fully elucidated. The major problems are that ferroelastic 90° domains are readily generated by small external forces and water in the crystal may cause dielectric anomalies. In this study, we observed the changes in the structural and dielectric properties in each domain using birefringence imaging with different temperatures. Furthermore, we have clarified the arrangements of the distorted CuCl6 octahedra using the angular dependences of g-values obtained from electron paramagnetic resonance (EPR) spectroscopy. Birefringence imaging is relatively insensitive to dielectric anomalies, while EPR spectroscopy is sensitive to them. Using the complementary nature of these methods, we have observed the previously reported structural phase transition at 232 K (≡ T3) and have proposed successful new structural models below T3. As for the ferroelectric phase transition, we find no anomalies at around 247 K (≡ T5). However, a birefringence anomaly indicating a ferroelectric phase transition appears at 25.8 K (≡ T6), and the appearance of a small spontaneous polarization is suggested below T6.

DOI： 10.7566/JPSJ.91.114701

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Stress-induced ferroelectric phase transition of SrTiO3 was microscopically observed using birefringence imaging techniques. Although there are many studies on ferroelectric state, the experiments under external force (abbreviated as σ converted to pressure) have been scarcely developed. This is because the dielectric and structural properties are locally disturbed by the nonuniform lattice distortion when σ is applied; however, it was not easy to quantitatively evaluate them. In this study, the spatial distribution of the dielectric and structural properties under s was clarified by retardance and fast-axis direction images. When σ ||[001], the ferroelectric state induced by normal stress appears almost uniformly below ~20K contrary to the coexistence of the ferroelectric and quantum paraelectric states under a high electric field. However, when σ || [110], both normal and shear stresses are simultaneously generated, resulting in the appearance of domains with complex shapes around dislocations in the tetragonal phase. Distributions of the retardance and the fast-axis direction exhibit concentration of the lattice distortion, and the structural phase transition temperatures are nonuniformly spread. From the temperature dependence of the retardance in each domain, there is no indication of the ferroelectric phase transition, probably because the lattice distortion never reaches the critical value.

DOI： 10.7566/jpsj.91.084704

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

We report experimental studies on Ru2-xFexCrSi focusing on properties related to antiferromagnetism in Ru2CrSi and spin glass (SG) in Ru1.9Fe0.1CrSi. By measuring the temperature dependence of magnetization M(T), specific heat C(T), electrical resistivity ρ(T), and muon spin relaxation (μSR), we observed that Ru2CrSi exhibited an antiferromagnetic (AF) transition at a temperature TN of ∼13 K, and Ru1.9Fe0.1CrSi showed SG properties that could be interpreted as successive SG transitions, where the spin-freezing occurred at temperature Tg, and below that strong irreversibility in M(T) and a gradual peak of M(T) at T∗(>Tg) appeared. When the data for 0≤x≤0.1 were compared, by substituting Fe the AF order was rapidly destroyed and it appeared to change to two anomalies at T∗ and Tg. With increasing x, there was a slight change in Tg from TN for x=0; however, T∗ increased, suggesting that the AF and the SG states are closely related. Furthermore, the results of specific heat, resistivity, and magnetization in high fields were presented and compared. For Ru2CrSi in specific heat under high magnetic fields up to 14 T, the peak shape around TN and the TN value were constant. The resistivity and magnetization in pulsed fields suggested that TN of Ru2CrSi was constant up to over 50 T. These results demonstrated the unusual robustness of the AF transition to magnetic fields. In Ru1.9Fe0.1CrSi, unusual hysteresis in magnetoresistance was observed in static and pulsed magnetic fields, although their appearances differed. These hystereses were considered a manifestation of the curious properties of the SG state with strong irreversibility.

DOI： 10.1103/PhysRevB.103.094428

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

The effect of chemical substitution on the ground state of the geometrically frustrated antiferromagnet CsCrF4 has been investigated through a neutron powder diffraction experiment. Magnetic Fe-substituted CsCr0.94Fe0.06F4 and nonmagnetic Al-substituted CsCr0.98Al0.02F4 samples are measured, and magnetic Bragg peaks are clearly observed in both samples. Magnetic structure analysis revealed a 120° structure having a magnetic propagation vector kmag=(0,0,1/2) in CsCr0.94Fe0.06F4. For CsCr0.98Al0.02F4, a quasi-120° structure having kmag=(1/2,0,1/2) is formed. It is notable that the identified magnetic structure in CsCr0.94Fe0.06F4 belongs to a different phase of ground states from those in CsCr0.98Al0.02F4 and the parent CsCrF4. These results suggest that the Fe substitution strongly influences the ground state of CsCrF4.

DOI： 10.1103/PhysRevB.102.174440

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Other Link： https://arxiv.org/abs/2011.06263

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Magnetic birefringence under mechanical stress is useful for investigating antiferromagnetically ordered spins. Although the stress is expected to lead to a single magnetic domain, intrinsic distributions of the birefringence appear because the stress causes a loss perpendicular to the applied stress σ. In this study, we used a stress-application apparatus that has been developed to use birefringence imaging techniques to demonstrate the stress-induced magnetic birefringence in KNiF3 under inhomogeneous stress. Using optical glass and yttria-stabilized zirconia, we confirm that applied stress up to 78 MPa is retained at temperatures down to ∼15 K. When a stress of 3 MPa is applied to KNiF3 below the Néel temperature TN = 246 K, the distribution of the retardance is homogeneous. The fast-axis direction is rotated by 90° below TN because the magnetic birefringence increases when sublattice magnetization develops. At 24 MPa, however, three types of fast-axis rotation areas appear, and we are able to observe the optical domain boundaries clearly.

DOI： 10.7566/JPSJ.88.124702

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Other Link： https://researchmap.jp/manaka_hirotaka/published_papers/26256204

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

A chemical-impurity substitution in a geometrical spin-frustrated antiferromagnet often produces an unconventional antiferromagnetic state, because the ground states of the pure systems maintain a delicate balance among the spins. To investigate the changes introduced by randomness in the antiferromagnetic ground states of triangular spin tubes, we synthesized polycrystalline samples of CsCr1−xAxF4 and α-KCr1−xAxF4 (A = Al, Ga, or Fe). In CsCr1−xAlxF4 and CsCr1−xGaxF4, a glass-like phase transition appears at Tg ∼ 5K. In CsCr1−xFexF4, the Cr3+–F−–Fe3+ (high-spin state) superexchange interactions along the tubes turn ferromagnetic. As a result, an antiferromagnetic phase transition is clearly observed at 4.5(1)K for x = 0.06, compared with CsCrF4. The obvious phase transition is attributable to the ferromagnetic interactions, which strengthen the in-plane magnetic anisotropy that stabilizes the quasi-120° spin structure. On the other hand, α-KCr1−xAxF4 (A = Al, Ga, or Fe) exhibited an antiferromagnetic phase transition, similar to that in α-KCrF4. Contrary to CsCr1−xFexF4, α-KCr1−xFexF4 retained the antiferromagnetic Cr3+–F−–Fe3+ (high-spin state) superexchange interactions.

DOI： 10.7566/JPSJ.88.114703

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：npj Quantum Materials  

Magnetic birefringence under mechanical stress is useful for investigating antiferromagnetically ordered spins. Although the stress is expected to lead to a single magnetic domain, intrinsic distributions of the birefringence appear because the stress causes a loss perpendicular to the applied stress σ. In this study, we used a stress-application apparatus that has been developed to use birefringence imaging techniques to demonstrate the stress-induced magnetic birefringence in KNiF3 under inhomogeneous stress. Using optical glass and yttria-stabilized zirconia, we confirm that applied stress up to 78 MPa is retained at temperatures down to ∼15 K. When a stress of 3 MPa is applied to KNiF3 below the Néel temperature TN = 246 K, the distribution of the retardance is homogeneous. The fast-axis direction is rotated by 90° below TN because the magnetic birefringence increases when sublattice magnetization develops. At 24 MPa, however, three types of fast-axis rotation areas appear, and we are able to observe the optical domain boundaries clearly.

DOI： 10.1038/s41535-019-0152-5

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AIP Publishing  

It has been shown that Fe2MnSi exhibits a ferromagnetic transition at Tc and an antiferromagnetic transition at a lower temperature, TA, to a phase referred to as the AF phase. In a recent study on Fe1.3Mn1.7Si, another antiferromagnetic transition at a temperature lower than TA, defined as TA2, was found, with the phase below TA2 referred to as the AF2 phase. In this study, magnetic properties of Fe3-xMnxSi are investigated for an x range of 1.65 ≤ x ≤ 1.85 in order to study theses transitions with varying x. For x ≥ 1.75, a transition characterized by a rather rapid decrease in the temperature dependence of magnetization is observed at a temperature lower than TA at fields higher than ∼2 T. This implies the AF2-AF transition exists for x ≥ 1.75 as for x = 1.7. The magnetic field where the AF2-AF transition occurs increases with x, whereas at lower fields TA2 does not depend strongly on x. Meanwhile, at near zero field, the ferromagnetic transition and spontaneous magnetization disappears for x ≥ 1.75, in contrast to the case for x = 1.7. This implies that the transition from paramagnetism directly to the AF2 phase occurs at low fields. These results are summarized in the B-T magnetic phase diagram.

DOI： 10.1063/1.5080429

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Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing Ltd.  

DOI： 10.1088/1742-6596/969/1/012153

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing Ltd.  

We have investigated the hyperfine coupling between Cs and Cr on the S = 3/2 equilateral triangular spin tube CsCrF4, utilizing 133Cs-NMR. At paramagnetic state above 80 K, we have obtained spectra containing a single peak, which reflects the single crystallographic Cs site. From the temperature dependence of the peak shift and peak width, we evaluated effective values of the isotropic and the anisotropic part of hyperfine coupling. The latter was compared with the calculated dipole contribution. Using obtained parameters with assumed spin structure, we tried to reproduce the broadened spectrum in the ordered state at 2.0 K. The preliminary analysis shows the 120-degree structure does not accord with the observed spectra at the ordered state.

DOI： 10.1088/1742-6596/969/1/012108

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing Ltd.  

Fe2MnSi exhibits a ferromagnetic transition at TC and another transition to a phase with antiferromagnetic components at a low temperature of TA . By substituting V for Mn, so as to obtain Fe2Mn1-xV x Si, TA decreases with x and then vanishes around x ∼ 0.2. In this study, the magnetic transitions are investigated by magnetization measurements for Fe2Mn1-xV x Si (y = 1, 0 ≤ x ≤ 0.2) in high magnetic fields up to ∼70 T and for Fe1.5(Mn1-xV x )1.5Si (y = 1.5, 0 ≤ x ≤ 0.1) up to 5 T. For y = 1.5, with increasing x, TC increases and TA decreases as for y = 1, and the rate of the decrease in TA with x is slightly smaller than for y=1. In the low magnetic field region, TA for y = 1 does not significantly change due to the magnetic field but a distinct decrease is observed in high fields. The critical field at 0 K of this transition in Fe2MnSi is found to be larger than 70 T, and with increasing x, the critical field decreases corresponding to the decrease of TA at zero field.

DOI： 10.1088/1742-6596/969/1/012099

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing Ltd.  

We developed a suitable sample stage that is optimized for birefringence imaging measurements at high electric fields (E ≃ 5 kV/cm) and low temperatures (T ≃ 20 K) to directly observe electric-field-induced ferroelectric domains in SrTiO . As a result, a huge retardance area corresponding to the ferroelectric domains appears at E ≥ 2 kV/cm and T ≤ 60 K even though the paraelectric domains partially remain. Furthermore, the fast-Axis direction drastically rotates by 90° at the ferroelectric phase transition temperature because of an electrostrictive effect in ferroelectrics. The phase diagram of the critical electric fields and temperatures agrees with previous reports obtained from dielectric and neutron scattering measurements. 3

DOI： 10.1088/1742-6596/969/1/012119

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

In the layered compound (C3H7NH3)2CuCl4, both electrical and magnetic effects are impacted by rotations of CuCl6 octahedra and alkylammonium chains (C3H7NH3) at successive structural phase transitions. However, below 132 K, the crystal structure remains unclear because the appearance of twin deformation and ferroelastic domains makes the arrangement of the CuCl6 octahedra and (C3H7NH3) chains difficult to resolve. Herein, a powerful approach combining birefringence imaging with electron paramagnetic resonance spectroscopy is employed to confirm the observed changes in crystal symmetry. Contrary to previous studies, birefringence imaging does not exhibit a significant decrease in the retardance and a switch of the fast-axis direction at around 132 K. Using electron paramagnetic resonance spectroscopy, the temperature dependence of the linewidth and the angular dependence of the g-value indicate that the structure below 132 K, previously determined via powder X-ray diffraction measurements, is not applicable. New structures are therefore proposed that are in agreement with the experimental results.

DOI： 10.7566/JPSJ.86.114710

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Other Link： https://researchmap.jp/manaka_hirotaka/published_papers/27837203

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier B.V.  

Two series of Heusler compounds Ru2Cr1−xXxSi (X = V, Ti) are synthesized, and their magnetic and electrical properties are investigated. Overall, these two series of compounds are identical in numerous properties. The measurements of magnetic properties reveal that an antiferromagnetic transition observed for x = 0 becomes smeared and it changes into a spin-glass state with increasing x. Around x = 0.5 this behavior disappears and it becomes paramagnetic. High-field magnetization for x = 0.3 and 0.4 up to 62 T exhibits no sign of magnetic transition or saturation of the magnetization. In the temperature dependence of resistivity, the kink that indicates the antiferromagnetic transition observed for x = 0 becomes invisible even for x ∼ 0.1. This also exemplifies that the antiferromagnetic order is destroyed by the substitution and is replaced by the spin-glass state. Concerning the resistivity, these samples exhibit semiconducting behavior for small x, whereas with increasing x ≳ 0.5 they turn to show metallic behavior and Ru2VSi becomes a paramagnetic metal. Nevertheless, Ru2TiSi shows a tendency for semiconductivity again.

DOI： 10.1016/j.jallcom.2016.09.276

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

Fe2MnSi exhibits a ferromagnetic transition at TC∼230 K and another transition to a phase with antiferromagnetic components at TA∼60 K. By substituting V for Mn, so as to obtain Fe2Mn1-xVxSi, TA is revealed to decrease with x and then vanish around x∼0.2. In this study, the phase boundary of the transition at TA in the high-field range is found for 0≤x≤0.15 with pulsed fields up to ∼70 T. The magnetization of Fe2Mn1-xVxSi slowly increases even at the highest field of ∼70 T, though it occurs more gradually as x increases. We compare the magnetization for 0≤x≤0.20 at 62 T with the Slater-Pauling rule, which holds when a Heusler compound is a half-metal, and find fairly good agreement. This suggests an intimate relation between the high-field phase and the half-metallic electronic structure, and that at the high-field limit the phase approaches the half-metallic state, which has been predicted by band-structure calculations.

DOI： 10.1103/PhysRevB.95.014410

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Birefringence imaging microscopy is well suited for comprehensively investigating various structural phase transitions but its weak point is that it imposes an inherent limit on the maximum retardance that can be detected. To detect retardance above this limit, we performed simultaneous birefringence measurements at multiple wavelengths on (CnH2n+1NH3)2MnCl4 with n = 1, 2, 3. For n = 1, we successfully detected large jumps in retardance (over six times greater than the limit) in the first-order phase transitions at Tc1 ≃ 88 K and Tc2 ≃ 251 K. For n = 2, a gradual change in retardance appears in the second-order phase transition at Tc = 214 K. High-definition images of optical fast-axis azimuths provided information on the misorientation of the alkylammonium chains. For n = 3, a retardance kink appears at Tc4 ≃ 152-155 K, and a retardance jump appears in the commensurate-incommensurate phase transition at Tc5 ≃ 96-99 K.

DOI： 10.7566/JPSJ.85.124701

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier B.V.  

The ground state of the frustrated equilateral triangular spin tube CsCrF4 is still hidden behind a veil though NMR spectrum broaden into 2 T at low temperature. In order to investigate the spin structure in an ordered state by 19F-NMR, we have determined the anisotropic hyperfine coupling tensors for each three fluorine sites in the paramagnetic state. The measurement field was raised up to 10 T to achieve highest resolution. The preliminary analysis using the obtained hyperfine tensors has shown that the archetypal 120°-type structure in ab-plane does not accord with the NMR spectra of ordered state.

DOI： 10.1007/s10751-016-1330-5

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Science International Journal  

We synthesized a quasi-two-dimensional Heisenberg antiferromagnet on a square lattice formed in α -RbCrF4 by improving the pretreatment method before primary sintering. From X-ray diffraction measurements, the crystal structure was found to consist of a TlAlF4-type structure, which shows a good two-dimensionality. But the splitting of the fundamental peak indicating a superstructure in the ab-plane appeared. Temperature dependence of magnetic susceptibility shows a broad peak, which indicates typical low-dimensional antiferromagnets, at Tmax ≈ 47K . Furthermore, a sharp peak which indicates an antiferromagnetic phase transition also appeared at TN = 29.3(2) K. Following several previous theoretical investigations, we estimated intra-layer (Jintra) and inter-layer (Jinter) exchange interactions to be Jintra/ KB = -6.6(1) K and Jinter / Jintra ≈ 0.05 , respectively. As a result, we found that α -RbCrF4 is a quasi-two-dimensional Heisenberg antiferromagnet.

DOI： 10.9734/PSIJ/2016/27184

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

Optical birefringence imaging systems demonstrate a high potential for comprehensively investigating various phase transitions. To completely demonstrate such abilities, the temperature dependence of birefringence (Δn) was measured in Δn ≃ 0 materials (i.e., cubic crystals with imperfect crystallization) via a background subtraction method. As a result, highly accurate birefringence imaging at 384 × 288 pixels was obtained using phase transition processes as well as varying temperatures visually characterized by the spatial distribution of not only the retardance level but also the optical fast-axis azimuth.

DOI： 10.1063/1.4958662

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DOI： 10.1103/PhysRevB.93.054425

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier B.V.  

In order to investigate the hyperfine coupling of three inequivalent 19F sites in the equilateral triangular spin-tube antiferromagnet CsCrF4, we have measured the temperature dependence of 19F-NMR Knight shift in the paramagnetic state above 20K. The hyperfine coupling constants for three F-sites were determined to be -0.170, 0.280 and -0.045 T/μB, and were found to be consistent with the observed spectra at 1.65K, where the system is possibly in the ordered state.

DOI： 10.1016/j.phpro.2015.12.094

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier B.V.  

In this study, the temperature (T) dependence of specific heat (Cp) is investigated in an equilateral triangular spin tube CsCrF4 above T = 0.38K under several magnetic fields (B). At B = 0 T, no λ-type anomaly of the temperature dependence [Cp(T)] appears over the entire temperature range. However, the DC and AC magnetic susceptibilities exhibit a small anomaly, which is interpreted as an antiferromagnetic phase transition at TN∼4.5K. This difference may indicate that the large magnetic entropy at B = 0 T is spent far below TN, because a large fluctuated spin state due to geometrical spin frustration may have occurred at T = 0K. Under different magnetic fields, the Cp(T)/T curves present shoulders and/or broad peaks above B = 1 T. The electronic specific heat coefficient decreases with increasing B indicating that the magnetic ground state consists of an antiferromagnetic ordered state with large spin fluctuations, rather than a gapless spin-liquid state, and their fluctuations are sensitively suppressed by the magnetic fields.

DOI： 10.1016/j.phpro.2015.12.093

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Physical Society of Japan  

The effects of Ni and Co substitution for the antiferromagnetic Heusler compounds Ru2CrZ (Z = Si or Ge) are studied by measuring magnetic and transport properties and specific heat. Ni substitution appears to not extensively affect the antiferromagnetic state. This contrasts sharply with the case for Ru2−xFexCrSi where spin-glass-like behavior was found. These results are further compared with those for Ru1.95Co0.05CrGe, indicating that the magnetic properties are largely changed by different substitutions in these compounds.

DOI： 10.7566/JPSCP.3.014024

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Applied Mathematics and Physics  

DOI： 10.4236/jamp.2014.27055

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Physical Society of Japan  

In this study the properties of Co1+δTiSb with excess Co are investigated. Results of X-ray diffraction measurements suggest that the C1b-type structure for δ = 0 is kept up to δ = 0.9 without impurity phases. On the other hand, with increasing δ a ferromagnetic component seems to develop and the conductivity becomes metallic. When the results of electron-probe-micro-analysis (EPMA) are considered together, these results appear to be well explained by considering that the excess Co exists in the grain boundaries between CoTiSb crystal grains as fine particles and shows superparamagnetism.

DOI： 10.7566/JPSCP.3.017017

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Open Journal of Physical Chemistry  

In material science, half filled 3d orbital of transition metals is essentially an important factor controlling characteristics of alloys and compounds. This paper presents a result of the challenge of excitation of inner-core electron system with long lifetime of zinc films. The advanced zinc films with excited inner-core electron, 3dn (n = 9, 8). We report experimental results of XPS measurements of 9 points in the sample along vertical direction, respectively. The most pronounced futures are existence of satellites, which are about 4 eV higher than the main lines. According to the charge transfer mechanism proposed by A. Kotani and K. Okada, it was clarified that the origins of these peaks are c3d9L for the main peak and c3d9 for the satellite, respectively. From the energy difference, δEB, and peak intensity ratio, I+/I-, between c3d9 and c3d10L, the energy for charge transfer, Δ, and mixing energy, T, were estimated. In the region where the intensity of c3d10L becomes large, Δ becomes small, 1.2 < Δ< 2.7, and T becomes small, too, 0.1 < T < 0.9, respectively. In this calculation, we supposed Udc = 5.5 eV and Udd = 5.5 eV. In the analysis along vertical direction, intensity profile of Zn3d9 showed odd functional symmetry and that of Zn3d10L showed even functional symmetry. Only the intensity profile of C1s (288 eV) showed the same spatial correlation with Zn3d9. In our experiment, the sample also showed high mobility of the constituting elements. These suggest that charge conservation in excited zinc atom suggests combination between Zn3d9 and C2-.

DOI： 10.4236/ojpc.2014.42007

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing Ltd.  

We have studied the microscopic magnetic state of a double perovskite Sr2FeMoO6 by x-ray magnetic circular dichroism (XMCD). An Fe L3,2-edge XMCD reveals that the formal Fe3+ ions have an appreciable orbital moment (morb) parallel to their large spin moment (mspin), showing the charge-transfer-induced, minority-spin (-) Fe t2g electrons. A weak but undoubted O K-edge XMCD was successfully detected, showing an O 2p-hole morb induced by 2p-3d hybridization. Along with information obtained from the observed Mo M3,2-edge XMCD, our findings verify the partially filled Fe 3d t2g-O 2pπ-Mo 4d t2g- hybridized bands at the Fermi level, which mediates ferrimagnetism.

DOI： 10.1088/1742-6596/502/1/012003

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The ground state of the quasi-one-dimensional system with bond-disorder (CH3)2CHNH3Cu(ClxBr1−x)3 with x = 0, 0.25 and 0.3 has been investigated by µSR. The Fourier spectrum of electron spin fluctuation in x =0.25 and 0.3 obtained by LF-µSR technique shows that there exists soft-mode toward a possible phase transition to an exotic phase such as Bose-glass. In gapped system with x = 0, the Fourier spectrum is totally different from the other two, indicating the existence of the quantum critical point at a finite x between 0 and 0.25.

DOI： 10.7566/JPSCP.2.010207

Other Link： https://arxiv.org/abs/1309.5480

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Korean Physical Society  

We performed temperature (T) dependence experiments on the AC magnetic susceptibility of equilateral and non-equilateral triangular spin tubes CsCrF4 and α-KCrF4, respectively. In α-KCrF4, the linear (X 0′) and the nonlinear (X 2′) magnetic susceptibilities show sharp peaks at 4.0 K, which corresponds to an antiferromagnetic phase transition. On the other hand, in CsCrF4, broad and positive X 0′ (T) peaks appear above f = 31 Hz at T ≃ 4 K, but no anomaly of X 0′ (T) occurs at f = 31 Hz. Furthermore, the X 2′ (T) curve at f = 977 Hz shows a broad and negative peak at T ∼3 K. We suspect that there is a gradual change in spin dynamics below T ≃ 4 K from the paramagnetic state at a high temperature to a slowly-fluctuating spin state without typical antiferromagnetic longrange order as one-dimensionality along the spin tubes coexists with geometrical spin frustration in the equilateral triangular planes.

DOI： 10.3938/jkps.62.2032

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We have performed multi-frequency electron spin resonance (ESR) and magnetization measurements on single crystals of the quasi one-dimensional magnet IPACu(ClxBr1-x)3 (x=0.83) in magnetic fields H along the b-axis at temperatures below an antiferromagnetic long-range ordering temperature (T N ≅ 13 K). We observed some ESR branches for typical antiferromagnetic modes with biaxial anisotropy at 1.5 K (≪ T N). We have analyzed the magnetization curve and the ESR excitation modes for H∥b by using a two sub-lattice model and obtained good agreement between experiment and calculation. In addition, we show that the origin of a field-induced magnetization jump is a spin-flop transition. These results show that the phase at temperatures below T N in this Cl-Br mixed compound can be described as a simple two sub-lattice antiferromagnet.

DOI： 10.3938/jkps.62.2073

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Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Korean Physical Society  

We performed X-ray diffraction, magnetic susceptibility, and magnetization experiments on nonequilateral triangular spin tubes composed of α-KCr1-xFexF4 (x = 0∼0.13), which consisted of one-dimensional Heisenberg antiferromagnets coexisting with geometrically-frustrated spin systems with bond randomness. The variation of lattice parameters with x may indicate that the Fe3+ ions constitute the low-spin state (S = 1/2). As a result of analyses of the frustration factor and the spin-flop transition field, we found that the effect of geometrical spin frustration was enhanced and that the magnetic anisotropy was weakened as x was increased. Because these results are remarkably similar to the previous results for α-KCr1-xAlxF4, the effect of the chemical impurity substitutions, whether they are magnetic or nonmagnetic ions, on α-KCrF4 is clearly understood.

DOI： 10.3938/jkps.62.2188

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

Magnetic nanocubes, with a controlled precursor molar concentration of ferric nitrate fixed at 0.004 M to ferrous chloride ranging from 0.002 to 0.01 M, were synthesized by a new simple colloidal method at 60 °C under 1 M alkaline condition. The metallic Au-ultrathin layer was successfully functionalized on the magnetic nanocubes surface for the fabrication of the core-shell structure (Fe3O4@Au) by the borohydrate reduction of HAuCl4 in water/poly-l-histidine solution. The functionalized core-shell structure with varying molar-ratios of Fe 3+/Fe2+ in aqueous media, core-shell structural characteristics (for example, size, morphology, and shell thickness), and physical properties (for example, crystalline, electronic, optical, and magnetic ones) of the resultant functional nanocubes were systematically investigated using UV-visible spectroscopy, SEM, TEM, XRD, XPS, EDX, and superconducting quantum interface device (SQUID) magnetometer analysis. The core-shell structure of Fe3O4@Au exhibits plasmonic properties with high magnetization and showed excellent hyperthermia-photothemal activity towards the cancer cell (HeLa) killing. For the hyperthermia killing of cancer cells under the alternating current magnetic field (AMF), the as-prepared Fe 3O4 exhibited higher activity than the Fe 3O4@Au nanoparticles. Interestingly, under the simultaneously combined AMF and photoirradiation with Fe3O 4@Au, much higher cancer cell killing was found than with only AMF induced hyperthermia killing. The promoting effect of an Au-ultrathin shell supported on Fe3O4 showed strong absorption in the visible region due to localized surface plasmon resonance and increased the hyperthermia-photothermal temperature with the photothermal stability of the Fe3O4@Au nanoparticles, rather than only Fe 3O4. It was found that the cell killing activity depends on the optical and magnetic properties of the Fe3O4@Au nanocubes. The optical and magnetic properties depended on the molar-concentration ratios of precursors of Fe(NO3) 3·9H2O and FeCl2·4H2O. The synthesized Fe3O4@Au nanocubes have great potential for a combination of cancer imaging and local treatment as a cancer cell killing paradigm of "see and treat" applications.

DOI： 10.1039/c3ra21479f

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

We have used a combination of neutron resonant spin-echo and triple-axis spectroscopies to determine the energy and linewidth of the magnon resonance in IPA-Cu(Cl0.95Br0.05)3, a model spin-1/2 ladder antiferromagnet where Br substitution induces bond randomness. We find that the bond defects induce a blue shift, δΔ, and broadening, δΓ, of the magnon gap excitation compared to the pure compound. At temperatures exceeding the energy scale of the interladder exchange interactions, δΔ and δΓ are temperature independent within the experimental error, in agreement with Matthiessen's rule according to which magnon-defect scattering yields a temperature independent contribution to the magnon mean free path. Upon cooling, δΔ and δΓ become temperature dependent and saturate at values lower than those observed at higher temperature, consistent with the crossover from one-dimensional to two-dimensional spin correlations with decreasing temperature previously observed in pure IPA-CuCl3. These results indicate limitations in the applicability of Matthiessen's rule for magnon scattering in low-dimensional magnets.

DOI： 10.1103/PhysRevB.87.020408

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Other Link： https://arxiv.org/abs/1211.4741

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Indian Academy of Sciences  

Magnetite (Fe3O4) nanoparticles were prepared by co-precipitation and hydrothermal methods and their phase transfer was done successfully to compare their performances in different aspects. Synthesized nanoparticles were characterized for XRD, FE-SEM, TEM, UV-Vis absorption (reflectance) spectra, magnetic hysteresis loops and a.c. magnetic field induced hyperthermia. The magnetic nanoparticles prepared by the co-precipitation method show superior performances in respect of heat dissipation capability, saturation of magnetization values and particle size when compared to those prepared by the hydrothermal method.

DOI： 10.1007/s12034-012-0414-3

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing Ltd.  

The Heusler compound Fe2MnSi exhibits a ferromagnetic transition at TC ∼ 220 K, and, below, another magnetic transition at T R ∼ 65 K, which is supposed to be a ferrimagnetic transition. In this study we investigate the effects of the substitution of Co and V for Fe and Mn, respectively, on these transitions. The temperature dependence of magnetization M(T) is measured for (Fe1-yCoy) 2MnSi (y < 0.1) and Fe2Mn1-xVxSi (x < 0.2). Substitution for both the cases leads to the fairy rapid decrease and the disappearance of TR. However, for Co-substitution T C increases rapidly but for V-substitution TC increases only slowly. The electrical resistivity ρ(T) of Fe2Mn 0.8V0.2Si is measured in magnetic field up to 9 T. From this it is found that TR is 6 K at 0 T and is absent at 7 T. The critical field of the transition for TR is estimated to be ∼ 7 T.

DOI： 10.1088/1742-6596/400/3/032021

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing Ltd.  

In this study the properties of the Heusler compounds Ru 2-xFexCrSi (0≤ x ≤ 0.1) are investigated. Ru 1.9Fe0.1CrSi was revealed to exhibit two anomalies in the temperature dependence of magnetization M(T); one is a peak in M(T) at T*N ∼ 30 K and the other is strong irreversibility in M(T) below T*N, the onset of which is defined as Tg. M(T) and specific heat CP(T) of Ru2CrSi are measured. A clear peak is observed in both M(T) and CP(T). This is in quite contrast to the case for Ru1.9Fe0.1CrSi, where no anomaly in C P(T) was observed at T*N or at any other temperatures. These indicate that an antiferromagnetic transition occurs at TN = 14 K in Ru2CrSi. For x = 0.02 the characteristic two anomalies in M(T) are also found at various magnetic fields, and their field dependence is basically the same as that for x = 0.1. These two anomalies are suggestive of successive spin-glass transitions. As for the dependence of the two anomalies on x, Tg does not change with x, whereas T*N decreases with decreasing x and seems to approach T g at zero field.

DOI： 10.1088/1742-6596/400/3/032020

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Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing Ltd.  

We performed X-ray diffraction and magnetization measurements on diluted triangular spin tubes made of α-KCr1-xAlxF 4. For α-KCrF4 (x = 0), successive antiferromagnetic phase transitions occurred at TN1 = 2.5(1) K and TN2 = 4.0(1) K, because superexchange interactions in each non-equilateral triangle lost their equilibrium below TN2. For 0 < x ≤ 0.10, the complex crystal structures are retained. When x increases, TN2 gradually decreases, but frustration factors indicating the magnitude of the geometrical spin frustration in each triangular plane increase. Because spin-flop transition fields dramatically decrease with increasing x, the substitution of Al 3+ for Cr3+ creates isotropic magnetic states. We suspect that the spin structure is strongly influenced by the slight distortion of CrF6 octahedra caused by a magnetoelectric linear effect.

DOI： 10.1088/1742-6596/400/3/032057

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing Ltd.  

We performed electron spin resonance (ESR) on polycrystalline S = 3/2 compounds consisting of equilateral and non-equilateral triangular spin tubes in CsCrF4 and α-KCrK4, respectively. In CsCrK 4, a gapless spin-liquid ground state was realized at 1.5 K. Linewidth of the ESR spectra dramatically increased below 100 K and appeared to diverge around 50 K although no magnetic long-range order occurred above 1.5 K. Furthermore, temperature dependence of integrated intensity of the ESR spectra indicates that the intrinsic ESR spectra can not be observed below 40 K. On the other hand, in α-KCrK4, successive antiferromagnetic long-range order occurred at TNI = 2.5(1) K and TN2 = 4.0(1) K. ESR spectra slightly change not only around TN2 but also around TN1. We considered that the spin structure in TN1 < T < T N2 may slightly change from the quasi-120° spin structure below TN1.

DOI： 10.1088/1742-6596/400/3/032049

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Current Nanoscience  

The current study was designed to find out the cancer cell killing efficacy of as-synthesized dumbbell-shaped Fe3O4 and gamma-Fe2O3 magnetic nanoparticles under AC (alternating current) magnetic-fields induction condition. Dumbbell-shaped Fe3O4 and gamma-Fe2O3 magnetic nanoparticles were successfully prepared by a modified hydrothermal method. Ferrous chloride tetrahydrate was solely used as a precursor for the nanomaterials. The as-synthesized nanomaterials were characterized by using XRD, FE-SEM and TEM. Dumbbell-shaped particle morphology was observed for the first time in all of iron oxides with magnetic properties. The particle size observed was 50-60 nm. The synthesized nanomaterials showed acceptable magnetization values when magnetic hysteresis loops were measured using a superconducting quantum interference device (SQUID) as well as colloidal stability. Moreover, the as-prepared magnetic nanoparticles suspensions showed significant temperature increments and cancer (HeLa) cell destroying potentiality (91% and 95% for Fe3O4 and gamma-Fe2O3, respectively) under an AC magnetic-field induction condition at room temperature using the concentration of 150 mu g/mL.

DOI： 10.2174/157341312803989051

Other Link： https://www.researchgate.net/publication/233959844_Synthesis_Characterization_and_Application_of_Dumbbell-shaped_Magnetic_Fe3O4_and_g-Fe2O3_Nanoparticles_Against_HeLa_Cancer_Cells

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2012  

In this current study we synthesized mixed α and γ-Fe 2O3 nanoparticles and their synergistic toxic effect against HeLa cells was investigated under ac (alternating current) magnetic-field induction and photoirradiation conditions at room temperature. The experiment was designed to find out the cancer cell killing efficacy of as-synthesized bare γ-Fe2O3, bare α-Fe 2O3 and mixed α and γ-Fe2O 3 nanoparticles under combined ac magnetic-field induction and photoirradiation conditions. The toxic effect of nanoparticles was obtained by counting the percentage of viable cells after all the treatments were completed using various concentrations. The results revealed that the highest toxic effect was obtained using mixed α and γ-Fe2O3 nanoparticles under combined ac magnetic-field induction and photoirradiation conditions at a dose of 60 μg mL-1 MEM (minimum essential medium), i.e., approximately 98% cancer cells were killed, whereas under only ac magnetic-field induction or only photoirradiation conditions, only 89% and 66% cancer cells were destroyed using the same dose of same nanomaterials, respectively. We also noticed that 55% and 79% cancer cells were destroyed using bare α-Fe2O3 and bare γ-Fe2O 3 nanoparticles, respectively, under combined ac magnetic-field induction and photoirradiation conditions using the same dose. To the best of our understanding, the mechanism or reason for almost 100% HeLa cell killing under the combined conditions can be ascribed to the combined or additive effect of ac magnetic-field induced hyperthermia and photocatalytic cytotoxicity.

DOI： 10.1039/c2nj40029d

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Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AIP Publishing  

In this report we propose a new idea to improve electron configuration of an atom and show the first apparent experimental data, which applies long-lifetime excited states of the inner-core electron system of atoms. For the next material-revolution from Carbon and Nuclear society to Hydrogen society, development of a high efficient and low cost hydrogen storage system is one of the most important key technologies. The surface reaction processes between hydrogen atoms and hydrogen storage alloys system are controlled by the number of d-electrons of transition elements, that is, perfectly or partly occupied. We confirmed the idea to change the number of d-electrons of zinc atoms by using the excitation of inner-core electrons due to surface-ion-recombination (SIR) process. Average density of Zn- was controlled by the electrostatic potential energy of a sapphire substrate and that of Zn+ ions was controlled by the collision frequency between Zn atoms and incident electrons. After SIR process, unique excited structures were confirmed at 10 eV, 90 eV, 100 eV, 140 eV, and 230 eV in XRD and ESR. These discreet energies are combination of binding energies of a zinc atom, 3d (10 eV), 3p (90 eV), and 3s (140 eV). From the selection rule Δl=±1, we can decide which ions are excited. Strong diffuse scatterings of X-rays show oriented defect structure due to excited molecules.

DOI： 10.1063/1.3667220

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Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing Ltd.  

A chemical impurity substitution in gapped spin-liquid ground states often leads to antiferromagnetic long-range order. However, few experimental studies have been conducted on the substitution effect in gapless spin-liquid ground states. We performed X-ray diffraction and magnetic susceptibility experiments on equilateral triangle spin tubes composed of CsCr1-xAl xF4 (x 0∼0.06). Because the gapless spin-liquid ground state is realized in CsCrF4 (CsCr1-xAlxF 4 with x = 0), for x > 0, we expected competition between the geometrical spin frustration in each triangular plane and the impurity-induced antiferromagnetic long-range order. We verified that for x 0∼0.06 no anomaly that indicates an antiferromagnetic long-range order appeared and that the gapless spin-liquid ground state was robust with respect to the effect of nonmagnetic impurity; we suggested that this is because geometrical spin frustration exists in the equilateral triangular plane.

DOI： 10.1088/1742-6596/320/1/012044

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Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing Ltd.  

Triangle spin tubes have attracted much attention because they possess characteristics of one-dimensional Heisenberg antiferromagnets along the tubes and geometrical spin frustration in each triangle plane. We performed X-ray diffraction, magnetic susceptibility, and heat capacity experiments on triangle spin tubes composed of CsCrF4 and α-KCrF4. In CsCrF4, no anomaly indicating an antiferromagnetic long-range order appeared, and a spin-liquid state was realized. In contrast, in α-KCrF4, antiferromagnetic long-range order occurred at T N2 = 4.0(1) K and another phase transition occurred at TN1 =2.5(1) K. Such successive phase transitions may suggest a simultaneous change of the spin and crystal structures owing to a magnetoelectric effect.

DOI： 10.1088/1742-6596/320/1/012043

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

We conducted X-ray diffraction, magnetic susceptibility, heat capacity, high-field magnetization, and electron spin resonance experiments on high-quality polycrystalline S = 3/2 compounds consisting of equilateral and non-equilateral triangular spin tubes in CsCrF4 and α-KCrF 4, respectively. In both compounds, geometrical spin frustration in the triangular planes coexists with one-dimensionality along the tubes. In CsCrF4, no magnetic long-range order appeared above 1.5K, which agrees with a prior report [H. Manaka et al.: J. Phys. Soc. Jpn. 78 (2009) 093701]. In a low temperature (T) regime, T-linear component of heat capacity appeared and magnetization curves showed finite initial slopes. As a result, CsCrF4 consists of a gapless spin-liquid state encompassing resonating spin-singlet pairs not only in each equilateral triangle but also along the tubes. In contrast, for α-KCrF4, successive magnetic phase transitions occurred at TN1 = 2.5(1) K and at TN2 = 4.0(1) K because superexchange interactions through three Cr-F-Cr paths in each non-equilateral triangle lost their equilibrium.

DOI： 10.1143/JPSJ.80.084714

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：International Journal of Technology  

Isolated atoms in group II-B such as zinc (Zn), cadmium (Cd), and mercury (Hg) are chemically stable. These atoms are important in the formation of excimer. Zinc in particular has been investigated by many researchers, as Zn2 excimer holds promise because of its long lifetime and its potential as an energy-storage system. However, excimer's benefits are based on excitation of the outermost electron. Our study confirmed the quantum dynamical condensation processes in which inner-core excitation arises due to ion-recombination between the vapor phase and the solid phase. The X-ray diffraction of the condensed structure of zinc film had included strong diffuse scattering depending on the incident energies. In this research, we produced the excited state of zinc excimer characterized by an extremely long lifetime. Intriguingly, a feature of the zinc film is that it transforms from metallic to insulative. It is thought that such a structure with this characteristic has been affected by electron spin and atomic distortion by inner-core excitation. The structure obtained in our experiment is expected to prove promising in engineering applications, such as electronics, spintronics, and batteries.

DOI： 10.14716/ijtech.v2i2.57

Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Trans Tech Publications, Switzerland  

In this paper we present experimental results with the ion recombination process in the vapor phase growth method. We consider the growth process of only one element case, Zinc, because of the clarification of the change of electron states in the element, not the entropy effect due to different elements. The advantages of using the ion recombination process are the following; 1) controllability of total energy, 2) the highest quenching rate, 3) locality of the collision. The total energy of the ion system was below 240 eV. Zn - ions exist on the growth front surface and Zn+ ones impinge to the growth surface from the vapor phase. The crystal structures of deposited zinc films are measured with the XRD system. Very strong diffuse scattering intensity of x-ray diffraction was observed at 10 eV, 90 eV, 100 eV and 230 eV after seven months "annealing" in room temperature from the preparation. These experimental facts suggest the effectiveness of the application of the excitation process of the inner core electron system as a new advanced material process. In this process, the ion recombination process and the existence of a metastable state are essentially important factors.

DOI： 10.4028/www.scientific.net/AMR.277.11

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

We have used a combination of neutron resonant spin-echo and triple-axis spectroscopies to determine the energy, fine structure, and linewidth of the magnon resonance in the model spin-1/2 ladder antiferromagnet IPA-CuCl 3 at temperatures T≪Δ0/kB, where Δ0 is the spin gap at T=0. In this low-temperature regime we find that the results deviate substantially from the predictions of the nonlinear sigma model proposed as a description of magnon excitations in one-dimensional quantum magnets and attribute these deviations to real-space and spin-space anisotropies in the spin Hamiltonian as well as scattering of magnon excitations from a dilute density of impurities. These effects are generic to experimental realizations of one-dimensional quantum magnets.

DOI： 10.1103/PhysRevLett.106.177202

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Other Link： https://arxiv.org/abs/1102.0214

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Springer Science  

The properties of Heusler compounds Ru 2-xFe x-CrGe are investigated and compared with those of Ru 1.9-Fe 0.1CrSi. Ru 2CrGe is confirmed to exhibit an antiferromagnetic transition with Neél temperature 13 K by magnetic susceptibility and specific heat measurements. When Fe is substituted for Ru, a peak in the magnetic susceptibility is observed, and in the lower temperature region irreversibility between temperature dependences of magnetization for zero-field-cooling and field-cooling conditions is found. Nevertheless, in specific heat of Ru 1.9Fe 0.1CrGe, there is no anomaly to indicate phase transition. The specific heat is almost identical to that for Ru 1.9Fe 0.1CrSi. The above results demonstrate that the magnetic states in the low temperature region of Fe-substituted samples are spin-glasslike states. Slight substitution of Fe for Ru destroys the longrange-order and lead to peculiar spin-glass-like states.

DOI： 10.1007/s10948-010-0967-6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

We carried out magnetization M(T) and specific-heat CP(T) measurements of the new Heusler compounds Ru2-x Fex CrSi (x=0.1, 0.3,and 0.5), which exhibit spin-glass freezing. M(T) has peak- and irreversibility-type anomalies. The temperatures at which these anomalies appear have magnetic field dependence described by the Gabay-Toulouse and de Almeida-Thouless lines in the low-field range. For the magnetic specific heat Cm(T), we did not observe a discontinuity indicating long-range magnetic phase transition but a broad hump characteristic of spin-glass freezing. Cm(T) in the low-temperature range is described as a combination of linear- and quadratic- T terms. The quadratic- T dependence of Cm (T) is probably associated with excitation of the Ising component of the freezing spins.

DOI： 10.1103/PhysRevB.82.024406

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

Spin dynamics of the square lattice Heisenberg antiferromagnet, Ba 2 MnGe2 O7, is studied by a combination of bulk measurements, neutron diffraction, and inelastic neutron-scattering techniques. Easy plane type antiferromagnetic order is identified at T≤4.0K. The exchange interactions are estimated as J1 =27.8 (3)μeV and J 2 =1.0 (1) μeV, and the saturation field HC is 9.75 T. Magnetic excitation measurements with high experimental resolution setup by triple axis neutron spectrometer reveals the instability of one magnon excitation in the field range of 0.7 HC 7Hc≤H≤0.85HC.

DOI： 10.1103/PhysRevB.81.100402

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Other Link： https://arxiv.org/abs/1102.0214

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

We report the single-crystal study of the bulk magnetization and neutron-scattering measurements on a quantum S=1/2 spin ladders system IPA-Cu (Cl0.95 Br0.05) 3 with quenched disorder. In zero field, the disordered spin liquid phase is preserved as in pure IPA-CuCl3. Due to the bond randomness, a different Bose glass phase was directly observed in Hc <H< H′, which separates the spin liquid phase from the unconventional Bose-Einstein condensation phase. The observed finite value of boson compressibility (dM/dH) and lack of field-induced three-dimensional long-range order are consistent with the theoretical prediction.

DOI： 10.1103/PhysRevB.81.060410

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Other Link： https://arxiv.org/abs/0909.1496

Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing Ltd.  

(CH3)2CHNH3Cu(ClxBr 1-x)3 abbreviated IPACu(ClxBr 1-x)3 is a mixed system of spin-gap compounds IPACuCl 3 and IPACuBr3. This mixed system is reported by macroscopic measurements to show a magnetic order when the value of x is between the quantum critical points (QCPs) 0.44 and 0.87. We have investigated microscopically the ground state of the samples x = 0.40, 0.45 and 0.50 which are located near the QCP of xc = 0.44, by Muon Spin Relaxation (μSR) and NMR measurements. For x = 0.40, μSR measurements in zero and longitudinal fields have shown that the spin fluctuation shows a significant slowing down with decreasing temperature, although the magnetic order does not appear down to T = 15 mK, indicating that the ground state is an exotic one rather than a gapped one. For x = 0.45 and 0.50, μSR and NMR measurements do not show any magnetic order at low temperatures, indicating that the QCP is larger than the reported value of xc = 0.44.

DOI： 10.1088/1742-6596/200/2/022036

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Topological effects on spin frustration in equilateral triangle S 1/4 3=2 spin tubes formed in CsCrF 4 were studied by magnetic susceptibility, heat capacity [CoTp], and electron spin resonance experiments. The experimental data show that there is no magnetic long-range order down to T 1/4 1: 3 K, and that no spin gap due to a chiral spin structure appears. Furthermore, since the CoTp curve has a T-linear component, a gapless spin-liquid ground state in one-dimensional antiferromagnets, the so-called Tomonaga-Luttinger liquid, is realized. This is characteristic of equilateral triangle spin tubes with S = half-integer.

DOI： 10.1143/JPSJ.78.093701

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Other Link： https://journals.jps.jp/doi/10.1143/JPSJ.78.093701

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

The results of a comprehensive study of the structural, magnetic, and magnetotransport properties of the Heusler compounds Ru2-x Fex CrSi are presented. The Fe-rich compounds (x 1.5) exhibit a usual ferromagnetic transition. The Ru-rich compound (x=0.1) does not show ferromagnetism but exhibits a peak in magnetic susceptibility at TN =30K. Nevertheless, specific-heat measurements show that there is no antiferromagnetic transition at TN nor at any other temperatures. With further decreasing temperature strong irreversible behavior occurs below a temperature Tg. It is proposed that these results can be interpreted as successive spin-glass transitions at TN and Tg. The compounds with intermediate x (=0.3 and 0.5) are found to be ferromagnetic. Both the saturation magnetization and the Curie temperature TC increase with increasing x. However, being different from the Fe-rich compounds, hysteresis of the magnetization is observed and this suggests that the ferromagnetism has glassy character. In lower-temperature range fairly large negative magnetoresistance are observed. These results are suggestive of a magnetically inhomogeneous ferromagnetic state, that is, the formation of ferromagnetic clusters.

DOI： 10.1103/PhysRevB.79.224423

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier B.V.  

Measurements of the macroscopic properties have indicated that the bond-disordered spin-gap system (CH3)2CHNH3-Cu(ClxBr1-x)3 is gapless when x is between 0.44 and 0.87. Using muon spin relaxation to investigate the microscopic properties of a sample with x=0.35, we observed a dynamical spin fluctuation, whose characteristic frequency decreased with decreasing temperature, indicating a magnetic ground state.

DOI： 10.1016/j.physb.2008.11.107

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Other Link： https://arxiv.org/abs/0811.0386

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

The spin-lattice relaxation rate T 1 -1 of 1H-NMR has been measured in (CH 3 ) 2CHNH 3Cu(Cl xBr l-x) 3 with x - 0 and 0.35, in order to investigate their microscopic magnetism. Previous macroscopic magnetization and specific heat measurements suggested that these two exist in a singlet-dimer phase. The temperature dependence of T 1 -1 in an x - 0 system decreased exponentially toward zero, providing microscopic evidence of a gapped singlet ground state, which is consistent with results of macroscopic experiments. At the same time, in the x = 0.35 system, T 1 -1 showed a sharp peak structure at approximately 7.5 K but no splitting of 1H-NMR spectra, indicative of magnetic ordering. We discuss the observed sharp peak structure in the x - 0.35 system with the soft mode toward the exotic magnetic ground state suggested by recent μSR experiments.

DOI： 10.1143/JPSJ.78.053702

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Other Link： https://arxiv.org/abs/0903.2318

Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing Ltd.  

Electron spin resonance (ESR) was performed on the mixtures of two spin-gap compounds IPA-Cu(ClxBr1-x)3 for 0.87 x < 1. Although the ESR line for x 1 split into two lines below 10 K, no splitting ESR lines appeared down to 1.4 K for x 0.99 and 0.98. This difference is due to bond randomness, i.e., a change from the pure spin-gap state to bond-randomness-induced disordered states.

DOI： 10.1088/1742-6596/150/4/042115

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing Ltd.  

From first-principle band structure calculations the Heusler alloys Fe 2MnSi and Co2MnSi are predicted to be half-metals, if the ferromagnetic state is assumed. In reality, however, Fe2MnSi exhibits a complex magnetic state with antiferromagnetic components, while Co 2MnSi is ferromagnetic with high Curie temperature and probably a half metal. In order to search better half-metals the alloys Fe 2-xCox MnSi are worth investigating. We have studied the magnetic properties of Fe2-xCo:cMnSi experimentally. With increasing Co concentration from x 0, the antiferromagnetic phase rapidly disappears. The saturation magnetization increases with increasing x. For x≥ 1.0 the saturation magnetizations agree well with those calculated theoretically. The dependence of the saturation magnetization on x is well described by the Slater-Pauling rule. This result suggests that Fe 2-xCoxMnSi is probably a half-metal for a wide range of x.

DOI： 10.1088/1742-6596/150/4/042099

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing Ltd.  

A percolated-induced ferromagnetic moment in KNixZn 1-xF3 for x = 0:57, which is Heisenberg-type diluted three-dimensional magnet, is studied by electron spin resonance. Below TC ≅ 24 K, ferrimagnetic resonance spectra appeared as expected. On the other hand, in KCoxZn1-xF3 for 0:49 x lt; 1, which are Ising-type diluted three-dimensional magnets, a percolated-induced ferromagnetic moment did not appear. This difference may play an important key role in Coulomb repulsion between Zn2+ ions because KNixZn1-xF3 consists of simple cubic lattice, on the other hand tetragonal distortion exists in KCoxZn1-xF3.

DOI： 10.1088/1742-6596/145/1/012080

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

One-dimensional random antiferromagnets (CH3) 2CHNH3Cu(ClxBr1-x)3 [abbreviated as IPA-Cu (ClxBr1-x)3] show three magnetic phases: Cl rich, intermediate, and Br rich. In this study, to confirm the presence of a gapped or gapless state in addition to a Bose-glass (BG) state of spin triplets at two magnetic phase boundaries, magnetic susceptibility, specific heat, and magnetization were measured. Contrary to our proposed model, the results suggest a gapless state and a BG state at the Br-rich phase boundary, and a spin-gap state at the Cl-rich phase boundary. From the viewpoints of the universality class, the BG state may be interpreted as a result of Anderson localization. Therefore, IPA-Cu (ClxBr 1-x)3 are intriguing compounds for studying the BG state because of good one dimensionality.

DOI： 10.1103/PhysRevB.79.092401

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CiNii Research

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

Inelastic-neutron-scattering and bulk magnetic-susceptibility studies of the quantum S=1/2 spin ladder system (CH3) 2CHNH3CuCl3 are performed under hydrostatic pressure. The pressure dependence of the spin gap Δ is determined. At P=1500 MPa it is reduced to Δ=0.79 meV from Δ=1.17 meV at ambient pressure. The results allow us to predict a soft-mode quantum phase transition in this system at Pc ∼4 GPa. The measurements are complicated by the proximity of a structural phase transition that leads to a deterioration of the sample.

DOI： 10.1103/PhysRevB.78.224409

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Other Link： https://arxiv.org/abs/0809.1254

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

The spin-gap system with a bond-disorder (CH3) 2 CHNH3 -Cu (Clx Br1-x) 3 is reported by experiments on macroscopic quantities of the uniform susceptibility and the specific heat to show a magnetic order at low temperatures (when the value of x is within the limited region between 0.44 and 0.87) and otherwise a gapped behavior. We have investigated microscopically the ground state of the sample with x=0.35 by muon spin relaxation (μSR) to observe that the frequency spectrum of the spin fluctuation tends to concentrate around zero energy as lowering temperatures. This behavior was interpreted as the soft mode toward the possible magnetic phase transition at absolute zero.

DOI： 10.1103/PhysRevB.78.054422

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Other Link： https://arxiv.org/abs/0807.3380

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

The mixtures of two spin-gap compounds IPA-Cu(ClxBr1-x)3 are studied by electron paramagnetic resonance and magnetization processes [M(H)]. From electron paramagnetic resonance spectra, the symmetry of the spin-gap state breaks down, even for x=0.99. From M(H) curves for x=0.95 and 0.92, however, spin gaps survive below μ0Hc1=10±1T, and the M(H) slopes bend at μ0Hc3=40±1T, below the saturation field Hc2. Such a curvature suggests an exotic phase transition: Bose-Einstein condensation of spin triplets occurs at Hc1<H<Hc3 and a Bose-glass state may be realized at Hc3<H<Hc2, successively. As a result, the possibility of fine-tuning the density of bosons by H provides a tool for determining the role of the interactions.

DOI： 10.1103/PhysRevLett.101.077204

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

Temperature dependencies of gap energies and magnon lifetimes are measured in the quasi-one-dimensional S=1/2 gapped quantum magnets (CH3)2CHNH3CuCL3 (IPA-CuCl3, where IPA denotes isopropyl ammonium) and Cu2Cl4•D8C4SO2 (Sul-Cu2Cl4) using inelastic neutron scattering. The results are compared to those found in literature for S=1 Haldane spin chain materials and to theoretical calculations for the O(3)- and O(N)- quantum nonlinear σ-models. It is found that when the T=0 energy gap Δ is used as the temperature scale, all experimental and theoretical curves are identical to within system-dependent but temperature-independent scaling factors of the order of unity. This quasi-universality extends over a surprising broad T range, at least up to κT∼1.5Δ.

DOI： 10.1103/PhysRevLett.100.157204

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Other Link： https://arxiv.org/abs/0711.4094

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Applied Physics Letters  

DOI： 10.1063/1.2884689

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

We succeeded in performing a magnetic conversion from transparent antiferromagnet KNi F3 to transparent ferrimagnets, with a spontaneous ferromagnetic moment by a percolation method. Considering Coulomb repulsion, the origin of the spontaneous ferromagnetic moment is explained by an inhomogeneous antiferromagnetic spin arrangement, even if nonmagnetic ions are dispersed homogenously over KNi F3. The ferromagnetic transition temperature was obtained to be 24-26 K. The transmittance at 600-1000 nm was excellent. This compound shows an alternative that can be used for an optical isolator that uses commercial semiconductor lasers, and can widely be used in next generation optical information networks.

DOI： 10.1063/1.2837540

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Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier Ltd.  

The ground state of the solid solution of the two spin gap systems (CH3)2CHNH3CuCl3 and (CH3)2CHNH3CuBr3 has been investigated by 1H NMR. The existence of a magnetic ordering in the sample with the Cl-content x=0.85 was clearly demonstrated by a drastic splitting in a resonance line at low temperatures below TN=13.5 K. The observed NMR spectra in the ordered state was qualitatively consistent with the simple antiferromagnetic state.

DOI： 10.1016/j.jpcs.2007.08.015

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Other Link： https://arxiv.org/abs/cond-mat/0610131

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

Inelastic and elastic neutron scattering is used to study spin correlations in the quasi-one-dimensional quantum antiferromagnet IPA-Cu Cl3 in strong applied magnetic fields. A condensation of magnons and commensurate transverse long-range ordering is observe at a critical field Hc =9.5 T. The field dependencies of the energies and polarizations of all magnon branches are investigated both below and above the transition point. Their dispersion is measured across the entire one-dimensional Brillouin zone in magnetic fields up to 14 T. The critical wave vector of magnon spectrum truncation is found to shift from hc ≈0.35 at H< Hc to hc =0.25 for H> Hc. A drastic reduction of magnon bandwidths in the ordered phase is observed and studied in detail. New features of the spectrum, presumably related to this bandwidth collapse, are observed just above the transition field.

DOI： 10.1103/PhysRevB.76.054450

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Other Link： https://arxiv.org/abs/0705.1360

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

DOI： 10.1143/JPSJ.76.085003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

The weakly coupled quasi-one-dimensional spin ladder compound (CH3)2CHNH3CuCl3 is studied by neutron scattering in magnetic fields exceeding the critical field of Bose-Einstein condensation of magnons. Commensurate long-range order and the associated Goldstone mode are detected and found to be similar to those in reference to spin-dimer materials. However, for the upper two massive magnon branches, the observed behavior is totally different, culminating in a drastic collapse of excitation bandwidth beyond the transition point.

DOI： 10.1103/PhysRevLett.98.167202

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Other Link： https://arxiv.org/abs/cond-mat/0608566

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

We synthesized a single-phase polycrystalline sample of a double-layer perovskite fluoride K3Cu2F7. This compound is the new member of the potassium copper fluoride family, which has an antiferrodistortive orbital order (AFDOO). Magnetic susceptibility measurements revealed that K3Cu2F7 is a rare experimental realization of antiferromagnetically isolated spin dimers on a simple double-square lattice with no frustration, and that AFDOO causes ferromagnetic interactions in respective layers. The coexistence of spin gap and AFDOO is an exotic phenomenon both in quantum spin systems and strongly correlated electron systems.

DOI： 10.1143/JPSJ.76.044710

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier B.V.  

We performed linear and nonlinear AC magnetic susceptibility measurements on Ca2 - x Lax MnO4 (x = 0.03, 0.07, 0.10, and 0.14). In such manganites, coexistence or competition brings about various phenomena. We focus on a cluster glass state consisting of ferromagnetic clusters within an antiferromagnetic matrix because the coexistence of the ferromagnetic double exchange interaction and the antiferromagnetic superexchange interaction is closely associated with phase separation. As a result, temperature (T) dependence of a linear susceptibility (X0′ (T)) exhibits a sharp peak for x = 0.03, and these peaks become broad with increasing x. The X0′ (T) curves for x = 0.07 and 0.10 show a typical frequency dependence around the peaks, suggesting a cluster (spin) glass transition. Furthermore, a nonlinear susceptibility (X2′ (T)) for x = 0.10 exhibits successive transitions: the ferromagnetic transition in each cluster occurs at ∼ 108 K and the antiferromagnetic transition between the ferromagnetic clusters occurs at ∼ 89 K. From the X0′ (T) and X2′ (T) curves for various values of x, we found the existence of the ferromagnetic clusters within the antiferromagnetic matrix, and the cluster glass state was realized for 0.07 ≤ x ≤ 0.14.

DOI： 10.1016/j.jmmm.2006.10.662

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Using a two-rotation-axis goniometer inserted into electron spin resonance equipment, for the first time, we successfully observed the three-dimensional distribution of the g-values of the composite Haldane spin chains in IPA-CuCl3. The result indicated that the Cu 3d hole orbital pattern spreads along a ladder-spin network plane. Furthermore, the superexchange interaction between the planes was not expected to be large as compared with that within the plane, irrespective of the Cu-Cu distance and the formation of superexchange paths.

DOI： 10.1143/JPSJ.76.023002

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Muon spin relaxation (μ+SR) measurements were performed on a S = 1 of composite Haldane spin chains in IPA-CuCl3, which consists of a spin-ladder network along the a-axis. At a zero external magnetic field, the μ+ spin relaxation became slightly faster with the development of a magnetic short-range order, but, as expected, oscillating spectra, which indicate a magnetic long-range order, did not appear. From the μ+SR time spectra under transverse and longitudinal magnetic fields, fluctuation of the local field whose frequency was estimated to be 99 ± 12 MHz was observed at 2.0 K, but it disappeared at 12 and 50 K. The appearance of the local field at a temperature between 12 and 2.0 K may suggest experimental evidence of the crossover from S = 1/2 spin state to S = 1 of composite Haldane spin state with decreasing temperature.

DOI： 10.1143/JPSJ.76.014704

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Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing Ltd.  

Magnetic torque τ and magnetostriction ΔL/L measurements were carried out in the spin gap system (CH3)2CHNH 3CuCl3. The magnetic torque shows a cusp-like anomaly at the magnetic field Ha1with increasing the magnetic field, and the magnetostriction shows a kink at almost the same magnetic field. These results suggest that anomalous change in the magnetic torque is associated with the lattice distortion, and it is expected that the field-induced magnetic phase transition is not simple Bose-Einstein condensation in this system.

DOI： 10.1088/1742-6596/51/1/043

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AIP Publishing  

The spin gap material IPA-CuCl3 has been extensively studied as a ferromagnetic-antiferromagnetic bond-alternating S = 1/2 chain. This description of the system was derived from structural considerations and bulk measurements. New inelastic neutron scattering experiments reveal a totally different picture: IPA-CuCl3 consists of weakly coupled spin ladders with antiferromagnetic legs and ferromagnetic rungs. The ladders run perpendicular to the originally supposed bond-alternating chain direction. The ferromagnetic rungs make this system equivalent to a Haldane S = 1 antiferromagnet. With a gap energy of 1.17(1) meV, a zone-boundary energy of 4.1(1) meV, and almost no magnetic anisotropy, IPA-CuCl3 may be the best Haldane-gap material yet, in terms of suitability for neutron scattering studies in high magnetic fields.

DOI： 10.1063/1.2355055

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Other Link： https://arxiv.org/abs/cond-mat/0506382

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

Soft x-ray magnetic circular dichroism (XMCD) measurements at the Co L 2,3 edges of Co-doped rutile TiO2 at room temperature revealed clear multiplet features characteristic of ferromagnetic Co 2+ ions coordinated by O2- ions, being in sharp contrast to the featureless XMCD spectrum of Co metal or metallic clusters. The absorption and XMCD spectra agree well with a full atomic-multiplet calculation for the Co2+ high-spin state in the D2h-symmetry crystal field at the Ti site in rutile TiO2. The results indicate that the ferromagnetism arises from the Co2+ ions substituting the Ti 4+ ions.

DOI： 10.1063/1.2236829

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Other Link： https://arxiv.org/abs/cond-mat/0603149

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing Ltd.  

The isomorphous compounds A2CuF4 (A ≤ K, Rb, Cs) are two-dimensional Heisenberg ferromagnets with the Curie temperatures of 6.25, 6.05 and 4.55 K, respectively. Previous studies showed that pressure-induced magnetic phase transitions occur in K2CuF4 and Rb 2CuF4 at around 10 GPa, above which the ferromagnetic behaviour disappears as a result of the structural change from antiferrodistortive to ferrodistortive order of the CuF6 octahedra in the basal plane. For Cs2CuF4 it was revealed that the interlayer exchange interaction changes from ferromagnetic to antiferromagnetic at a certain pressure below 2.2 GPa. Motivated by this unexpected result, we have carried out magnetic measurements on Cs2CuF4 in a diamond-anvil cell at various pressures up to 26 GPa by using a superconducting quantum interference device vibrating coil magnetometer. It was found that the Néel temperature increases with pressure at a rate of 0.3 K GPa -1 up to 17 GPa, reaches a maximum of about 9 K at around 17 GPa and then decreases rapidly to zero. At pressures above 21 GPa the magnetic susceptibility decreases to the background level, strongly suggesting that a structural change similar to those observed for the other two compounds occurs for Cs2CuF4 at around this pressure.

DOI： 10.1088/0953-8984/18/11/001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

We studied the electronic states and magnetic moments of a bcc-Co(001) monatomic layer facing an amorphous Al-O tunneling barrier using x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) at the L2,3 core edges of Co. Both the XAS and XMCD measurements revealed that 1 monolayer (ML) Co is not oxidized. The magnetic moment of 1 ML bcc Co(001) facing the amorphous Al-O was observed to be almost the same as that of bulk Co. In contrast, the total magnetic moment of 1 ML bcc Co(001) facing a metallic Al layer was reduced by the effect of the proximity to Al atoms.

DOI： 10.1063/1.2200407

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

Magnetic excitations in the quasi-one-dimensional antiferromagnet IPA-CuCl3 are studied by cold neutron inelastic scattering. Strongly dispersive gap excitations are observed. Contrary to previously proposed models, the system is best described as an asymmetric quantum spin ladder. The observed spectrum is interpreted in terms of composite Haldane spin chains. The key difference from actual S=1 chains is a sharp cutoff of the single-magnon spectrum at a certain critical wave vector.

DOI： 10.1103/PhysRevLett.96.047210

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Other Link： https://arxiv.org/abs/cond-mat/0511143

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：INTERMAG ASIA 2005: Digests of the IEEE International Magnetics Conference  

DOI： 10.1109/intmag.2005.1464432

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier B.V.  

We have studied the electronic state of a Co(001) monatomic layer facing an amorphous-Al2O3 tunneling barrier using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) measurements at the Co L2,3 edges. XAS and XMCD measurements evidence that the 1-ML Co facing Al2O3 layer is not oxidized.

DOI： 10.1016/j.jmmm.2003.12.279

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier B.V.  

We report on zero-field (ZF) and longitudinal-field (LF) dependence of μ+SR time spectra at 2.0, 12 and 50 K in (CH3) 2CHNH3CuCl3, which consists of ferromagnetic-antiferromagnetic alternating Heisenberg chains with S=12. As a result, the ZF-μ+SR time spectra showed that the relaxation rate which was due to electron spins slightly increased with decreasing temperature. Furthermore, from the analysis of the LF-μ+SR time spectra, the fluctuation of the local field which was due to electron spins appeared at 2.0 K but it disappeared at 12 and 50 K.

DOI： 10.1016/j.jmmm.2003.12.664

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

We report on a study of the polarization dependence of the x-ray absorption spectra (XAS) at the Cu L2,3 edges and the F K edge in single crystals of two-dimensional ferromagnets A2CuF4 (A=K, Cs). We successfully observed polarization-dependent XAS at the Cu L2,3 edges. This provides experimental support of the antiferrodistortive orbital ordering (AFDOO) model proposed by Khomskii and Kugel [D. I. Khomskii and K. I. Kugel, Solid State Commun. 13, 763 (1973)]. We also observed polarization dependence of the XAS at the F K-edge peak at ∼681 eV, which reveals the F 2pσ-hole orbitals arising from Cu 3d-F 2p hybridization. We argue its implication in relation to the realization of AFDOO.

DOI： 10.1103/PhysRevB.68.184412

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

DOI： 10.1143/JPSJ.72.2694

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier B.V.  

Mixed magnetic systems (CH3)2CHNH 3Cu(ClxBr1-x)3 over the intermediate phase (0.44<x<0.87) are good candidate compounds for experimental studies on the gapless state induced by bond randomness. We performed measurements of the magnetization process at 1.7 K on these mixed compounds. As a result, a typical spin flop transition, which indicated absence of the energy gap, was detected. From the variation in the spin flop transition field with x, the expected value of spins 〈Siz〉 was found to reach its maximum at x≃0.71, the point at which bond randomness is highest.

DOI： 10.1016/S0921-4526(02)02035-5

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier B.V.  

The compound (CH3)2CHNH3CuCl3 consists of ferromagnetic and antiferromagnetic alternating Heisenberg chains with S = 1/2; a pair of ferromagnetically coupled spins behaves as a spin with S = 1. Consequently, it has the Haldane gap in its energy spectrum at T = 0 K. We investigated an issue what will happen when Cl ions are randomly replaced by other kind of anions, for instance by Br ions. Performing experiments on single crystals of mixed compounds (CH3)2CHNH3Cu(ClxBr1-x) 3 in which Cl ions are randomly replaced by Br ions, we found that the energy gap disappeared over the region 0.44<x<0.87. The experimental data, which prove the disappearance of the energy gap, are presented and discussed.

DOI： 10.1016/S0304-8853(02)00992-7

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

DOI： 10.1143/JPSJ.71.2822

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

Mixed magnetic systems (formula presented) are good candidates for experimental studies of the effect of bond randomness in both the Haldane state and the singlet dimer state. We investigated the magnetization process in these mixed compounds with various values of (formula presented) under an external field up to 41 T at 1.7 K. As a result, the existence of a finite energy gap was confirmed for (formula presented) while a typical spin flop transition, which indicates absence of the energy gap, was detected for (formula presented) From the variation of the spin flop transition field with x, the expected value of spins (formula presented) was found to reach its maximum at (formula presented) the point at which bond randomness is highest. For (formula presented) on the other hand, the magnetization curves showed indistinct increases, which made it difficult to ascertain whether the energy gap exists.

DOI： 10.1103/PhysRevB.66.064402

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

The dependence of optical linear birefringence Δn on temperature T was measured on a single crystal of (CH3)2 CHNH3CuCl3, which consists of ferromagnetic-antiferromagnetic (F-AF) alternating Heisenberg chains with S = 1/2. The curve of dΔn(T)/dT showed a large peak near 25 K and a small shoulder near 45 K. The presence of these two anomalies is qualitatively similar to the theoretical curve of the magnetic specific heat in ferromagnetic-dominant F-AF chains.

DOI： 10.1143/JPSJ.70.2509

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

The electron-spin-resonance (ESR) and dc magnetization measurements of the spiel-type compound LiCuVO4 in a temperature range 2-300 K are presented. At cooling, the magnetization shows a broad maximum at TM=28 K, characteristic of a quasi-one-dimensional magnetic system. Then, the magnetization somewhat increases at temperatures below ∼9 K, shows a second maximum at TN′ ∼4 K, and a subsequent sharp drop. Both magnetization and ESR data indicate that the three-dimensional antiferromagnetic ordering occurs at TN = 2.3 K. Above TN the asymmetric ESR spectra of the LiCuVO4 powder sample are in correspondence with the symmetry of the crystal field on Cu2+ ions. The g∥ and g⊥ values diverge at cooling as is anticipated for a quasi-one-dimensional Heisenberg antiferromagnet. According to the Bonner-Fisher model the interchain exchange interaction is J1 = 22 K, while the intrachain exchange interaction is estimated to be J2 ∼1 K.

DOI： 10.1103/PhysRevB.64.024419

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Electron paramagnetic resonance measurements were performed at 24 GHz on the magnetic compound (CH3)2CHNH3CuBr3, which consists of antiferromagnetic-antiferromagnetic alternating Heisenberg chains. The results are compared with those obtained for ferromagnetic-antiferromagnetic chains (CH3)2CHNH3CuCl3 reported in Phys. Rev. B 62 (2000) 14279. The absorption intensity, after showing a broad maximum around 70 K, decreases to zero when the temperature approaches 0 K. Contrary to the case in the Cl compound in which the absorption line splits into two lines around 10 K. a single absorption line persists down to 1.4 K, the lowest temperature of these experiments. These results are interpreted to result from formation of singlet dimers at low temperatures. The Dzyaloshinsky-Moriya exchange interaction is strongly suggested to be the main perturbation term from the analysis of the dependence of linewidth and resonance field on temperature.

DOI： 10.1143/JPSJ.70.1808

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

At ambient pressure, both the intralayer and the interlayer exchange interactions in the layered compound (CH3NH3)2CuCl4 are ferromagnetic. Magnetic susceptibility and neutron scattering experiments performed under pressures up to about 1 GPa revealed that the interlayer exchange interaction turns into an antiferromagnetic one at a pressure between 0.41 GPa and 0.61 GPa. while the intralayer exchange interaction remains ferromagnetic. The spin structure in the antiferromagnetic phase is still collinear at least up to 1.1 GPa.

DOI： 10.1143/JPSJ.70.1390

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier B.V.  

The ground states of the ferromagnetic-antiferromagnetic alternating chains (CH3)2CHNH3CuCl3 (abbreviated as IPACuCl3) and the antiferromagnetic-antiferromagnetic alternating chains IPACuBr3 are recognized as the Haldane state and the singlet dimer state, respectively. We are interested in how the ground state changes in IPACu(ClxBri1-x)3 when x is varied. From the magnetic susceptibility and specific heat measurements, the mixed systems for 0.83 ≥ x ≥ 0.56 were found to lose the energy gap even at H = 0. We think that the gapless state is caused by the randomness of the intrachain exchange interactions. © 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(00)01195-1

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

The compound (CH3)2CHNH3CuCl3 consists of ferromagnetic and antiferromagnetic alternating Heisenberg chains with S=1/2. According to recent electron spin resonance (ESR) experiments at 24 GHz, a pair of ferromagnetically coupled two spins, which is expressed as Ŝ≡S1+S2, behaves as a spin with Ŝ = 1 below 10 K, and therefore the magnetic ground state in this compound is the Haldane state. Then the dipole-dipole interaction and the anisotropic-exchange interaction between ferromagnetically coupled two spins act as a fictitious single-ion anisotropy, which removes the threefold degeneracy of the triplet state. To confirm the energy scheme of the nondegenerate triplet state, high-field and high-frequency ESR experiments up to 20 T and 540 GHz were performed on the single crystals. The absorption due to the Ŝz=-1↔Ŝz=0 transition in the triplet excited levels was observed below 330 GHz and 10 K. The sign and the value of the fictitious single ion anisotropy were determined to be D*/gμB=-0.24 to -0.48 T at 1.7 K. At 427.6 GHz and under an external field near 15 T, where the field-induced gapless state is formed, the absorption line that was thought to be antiferromagnetic resonance was observed at 1.7 K.

DOI： 10.1103/physrevb.63.144428

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Doctoral thesis  

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

The isomorphous compounds (CH3)2CHNH3CuCl3 and (CH3)2CHNH3CuBr3 consist of ferromagnetic-antiferromagnetic and antiferromagnetic-antiferromagnetic alternating Heisenberg chains with S = 1/2, respectively. The ground state is therefore regarded as the Haldane state in the former and the singlet dimer state in the latter. To clarify the effect of bond randomness on the Haldane state as well as on the singlet dimer state, the magnetic states of the random alternating Heisenberg chains (CH3)2CHNH3Cu(ClxBr1-x)3, i.e., mixed systems of the two compounds mentioned above, were investigated. From magnetic susceptibility and specific heat measurements, it was confirmed that a gapless phase appears over the intermediate region 0.44 < x < 0.87. At the two boundaries, i.e., the boundary between the Haldane phase and the gapless phase and that between the gapless phase and the singlet dimer phase, the energy gap abruptly becomes zero. This study clarifies that bond randomness wipes out the energy gap in both the Haldane state and the singlet dimer state, when the strength of bond randomness exceeds a certain value.

DOI： 10.1103/PhysRevB.63.104408

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

In the two-dimensional Heisenberg antiferromagnet (C2H5NH3)2CuCL4, the intralayer exchange interaction is ferromagnetic, whereas the interlayer exchange interaction, which is less than 10-4 of the intralayer one, is antiferromagnetic, and the spins collinearly lie in each layer. To investigate the effect of pressure on its spin structure, magnetic susceptibility and neutron scattering measurements under pressures up to 2.5 GPa were performed. The magnetic susceptibility measurements revealed the appearance of a pressure-induced weak ferromagnetic moment along the c-axis around 0.6 GPa. The neutron scattering measurements clarified the noncollinear spin structure which causes the weak ferromagnetic moment mentioned above. That is, the ferromagnetically coupled spins in each layer cant from the layer, which brings about the weak ferromagnetic moment along the c-axis. The ferromagnetic coupling in each layer and the antiferromagnetic coupling among the nearest-neighboring layers are maintained at least up to 2.5 GPa.

DOI： 10.1143/JPSJ.70.241

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

The compound (CH3)2CHNH3CuCl3, which consists of ferromagnetic-dominant ferromagnetic and antiferromagnetic alternating Heisenberg chains with S= 1/2, is regarded as a Haldane system with S= 1 at low temperatures because a pair of ferromagnetically coupled spins behaves as S= 1. There should therefore be a crossover of the spin state from S= 1/2 to S= 1 when the temperature is decreased. With the expectation that the crossover causes a drastic change in spin dynamics, electron paramagnetic resonance (EPR) experiments were performed at 24 GHz on single crystals of this compound over the region of 1.4-295 K. The EPR spectra observed below 10 K were found to show characteristics clearly distinct from those above 10 K. That is, a single absorption line observed above 10 K was found to split into two lines below 10 K, and an additional weak line appeared at a position corresponding to half of the averaged resonance fields of the two lines. The resonance fields of the two lines vary with the direction of the external field H; their angular dependence is a±b(1-3 cos2 θ), where a and b are constants, and θ is the angle between the direction of H and one of the normals of the orthogonal crystal surfaces. The resonance field of the weak line that appeared at the half-field position was almost constant with respect to the direction of H. These experimental results observed below 10 K are explained when one considers that the S= 1 state caused by pairs of ferromagnetically coupled two spins supersedes the S= 1/2 state of the individual spins. Then the dipole-dipole interaction (H'DD) and the anisotropic exchange interaction (H'AE) between ferromagnetically coupled two spins act as a fictitious single ion anisotropy, and remove the threefold degeneracy of the triplet state of S= 1, i.e., Es,sz = E1,1,E1.0, and E1,- 1. As a result, the ASz=±1 transitions, i.e., the transitions between E1,-1 and E1.0, and between E1,0 and E1,1 bring about two absorption lines. That is why the two lines appear below 10 K. The weak half-field line is due to the ASz=±2 transition, which is also caused by H'DD and H'AE between ferromagnetically coupled two spins because nondiagonal elements between |1,1〉 and |1,- 1〉 are not 0.

DOI： 10.1103/PhysRevB.62.14279

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：High Pressure Research  

The two-dimensional Heisenberg antiferromagnet (C2H5NH3)2CuCl4 has the ferromagnetic intralayer exchange interaction, while the extremely weak interlayer exchange interaction is antiferromagnetic. Neutron scattering experiments under high pressures have been performed on this compound. We confirm that the spin structure changes around 1∼2 GPa from the collinear alignment along the a-axis to a spin-canting one. The weak moment due to the canting is parallel to the c-axis. The results indicate that the ferromagnetic intralayer and the antiferromagnetic interlayer exchange interactions are maintained up to 1∼2 GPa. Why the weak ferromagnetic moment along the c-axis occurs is due to a lowering of crystal symmetry by pressure.

DOI： 10.1080/08957950008245906

Scopus

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：High Pressure Research  

Neutron scattering experiments on the two-dimensional Heisenberg ferromagnets Cs2 CuF4 and K2CuF4 have been performed around 2∼3GPa over 1.4-15K. At ambient pressure both the intralayer and the interlayer exchange interactions in these two compounds are ferromagnetic. At about 2 GPa, the interlayer exchange coupling in Cs2 CuF4 is found to change from ferromagnetic to antiferromagnetic, while the ferromagnetic intralayer exchange interaction is maintained. Contrary to Cs2CuF4, the ferromagnetism in K2CuF4 is not destroyed by pressure up to 9 GPa, that was confirmed in the early study of the magnetic susceptibility measurements.

DOI： 10.1080/08957950008245904

Scopus

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier B.V.  

The compound (CH3)2CHNH3 CuCl3, which consists of ideal ferromagnetic-dominant ferromagnetic and antiferromagnetic alternating Heisenberg chains with S = 1/2, is expected to behave as S = 1/2 at high temperatures. At low temperatures, however, a pair of ferromagnetically coupled spins behaves as S = 1. To confirm this expectation, EPR experiments are performed on this compound. As a result, the spin relaxation phenomena drastically change around 10 K. From the analysis of the spectra, we conclude that the Haldane state is realized below 10 K.

DOI： 10.1016/S0921-4526(99)02706-4

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier B.V.  

An antiferromagnetic transition in the quasi-one-dimensional metaloxide compound LiCuVO4 was found. A broad maximum of the magnetic susceptibility was observed at TM= 28 K, while at T′N = 4 K the magnetic susceptibility exhibits a sharp decrease. The Néel temperature TN = 3.3 K increases initially with magnetic field, and then decreases. The exchange interaction integral in the chains of edge-sharing CuO6 octahedra and the interchain interaction integral are estimated to be J1 = 22.5 K and J2 = 1.3 K, respectively. © 2000 Published by Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(99)02739-8

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

We report measurements of the magnetization process of the gap system (CH3)2CHNH3CuCl3. in which ferromagnetic-dominant ferromagnetic and antiferromagnetic alternating Heisenberg chains are formed and then a pair of ferromagnetically coupled S=1/2 spins behaves as a spin of S=1. The two critical fields Hc1 and Hc2, corresponding to the elimination of the energy gap and the alignment of all the spins along the direction of an external field H, are detected at 10.4 T and around 44 T, respectively, on a scale of the reduced magnetic field gH/2. These values are, in principle, consistent with those estimated from the analysis of the magnetic susceptibility. The critical exponents in the formula such as M(H) ∝ (H - Hc1)1/δ1 and 1 - M(H) ∝ (Hc2 - H)1/δ2 are found to be δ1 > 1 and δ2 > 1.

DOI： 10.1143/JPSJ.69.675

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Electron spin resonance experiments were performed on α′-NaV2O5, a possible spin-Peierls compound, at 9.3 and 23.5 GHz over 1.3-700 K. Analyzing all factors of the absorption line above Tsp = 34 K, such as the value and the angular dependence of the linewidth at high temperatures, the temperature dependence of both the linewidth and the resonance field, as well as the high temperature lineshape, we find that the exchange-narrowing theory closely explains these factors when a linear Heisenberg chain with S = 1/2 along the b-axis is assumed, and the antisymmetric exchange interaction, Σidii+1 · (Si × Si+1) with di+1//c-axis, between nearest-neighbor spins on the b-axis is adopted as the origin of line broadening. As long as the results of this study are concerned, the model of V4+ magnetic chains separated by nonmagnetic V5+ chains in the ab-plane above 34 K is acceptable. However, the results do not necessarily deny a V-O-V molecular spin model that has been proposed to account for a new crystal structure formed by only one distinct V site, because the molecular spin model, as shown in recent theoretical papers, leads to antiferromagnetic Heisenberg linear chains along the b-axis. If an effective antisymmetric exchange interaction between the molecular spins is proven to exist, it can be an origin of the line broadening of this compound.

DOI： 10.1143/JPSJ.67.4269

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier B.V.  

We report, on the basis of magnetic susceptibility measurements, that the S = 1/2 compound (CH3)2CHNH3CuCl3 (IPACuCl3) forms ferromagnetic and antiferromagnetic alternating linear chains with J1/k = - 23.5 K and J2/k = + 54.1 K, which indicate that a pair of ferromagnetically coupled spins behaves as a spin of S = 1. This compound can, therefore, be discussed in terms of the Haldane conjecture for integer spins. The energy gap is estimated to be 17.1-18.1 K. On the contrary, the isomorphous compound IPACuBr3 is found to form antiferromagnetic and antiferromagnetic alternating chains with J1/k = - 61 K and J2/k = - 33 K; the energy gap is estimated as 98 K.

DOI： 10.1016/S0304-8853(97)00477-0

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Since the ferromagnetic intralayer exchange interaction in K2CuF4 is due to the antiferrodistortive (AFD) orbital ordering of the 3d holes of Cu2+ ions, we expect that the ferromagne ism of this compound to disappear when the AFD order of the distortion of CuF6 octahedra collapses. Recent magnetic susceptibility measurements performed at high pressures on this compound actually confirmed the disappearance of the ferromagnetism above approximately 9 GPa [M. Ishizuka et al.: J. Phys. Soc. Jpn. 65 (1996) 1927]. To obtain evidence of the pressure-induced structural change which corresponds to the magnetic change mentioned above, we measured the pressure dependence of the phonon-Raman spectra of this compound. As a result, we found that the scattering lines relevant to the vibrational modes of CuF6 octahedra ordered in the AFD fashion disappeared above 9 ∼ 10 GPa. This result is consistent with the structure above 9 GPa revealed by recent X-ray diffraction experiments that we performed.

DOI： 10.1143/JPSJ.66.2989

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

We report that antiferromagnetic and antiferromagnetic (AF-AF) alternating Heisenberg chains with S = 1/2 are formed in (CH3)2CHNH3CuBr3, which is in contrast to the almost isomorphous compound (CH3)2CHNH3CuCl3, because the Cl compound forms ferromagnetic-dominant ferromagnetic and antiferromagnetic (F-AF) alternating Heisenberg chains [H. Manaka et al.: 3. Phys. Soc. Jpn. 66 (1997) 564]. From the analysis of the dependence of magnetic susceptibility on temperature, χ(T), the two different antiferromagnetic exchange interactions defined in the Hamiltonian H = -2J1 Σ S2i · S2i+1 - 2J2 Σ S2i · S2i-1 are determined to be J1/k = - 61 K and J2/k = -33 K. Applying the low temperature experimental data to the formula χ(T) ∝ T-1/2 exp(-Δ/kT), we estimate the energy gap Δ to be 98 K. We discuss why AF-AF and F-AF alternating chains are formed in the Br and the Cl compounds, respectively, in spite of their almost isomorphous crystal structures.

DOI： 10.1143/JPSJ.66.1908

Web of Science

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

On measuring the dependence of the magnetic susceptibility of (CH3)2CHNH3CuCl3 on the temperature, we find that this compound forms ferromagnetic and antiferromagnetic alternating linear chains with S = 1/2. The magnetic susceptibilities observed in external fields applied along three different surfaces of an as-grown single-crystal sample show broad peaks at around 24 K and steeply decrease to zero with further decreases in temperature toward 0 K. Two types of superexchange interactions defined in the Hamiltonian [formula omitted] are determined to be J1/k = -23.5 K and J2/k = +54.1 K, which indicates that a pair of ferromagnetically coupled spins behaves as a spin of S = 1 and thus this compound is regarded as antiferromagnetic linear chains with S = 1. The present system can therefore be discussed in terms of the Haldane conjecture for integer spins. The energy gap is estimated to be 17.1～18.1 K.

DOI： 10.1143/JPSJ.66.564

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Event date： 2025.9 - 2024.9

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Venue：石川   Country：Japan  

DOI： 10.11316/jpsgaiyo.71.2.0_828

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DOI： 10.11316/jpsgaiyo.71.2.0_2552

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DOI： 10.11316/jpsgaiyo.71.1.0_1082

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DOI： 10.11316/jpsgaiyo.71.1.0_1220

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DOI： 10.11316/jpsgaiyo.71.1.0_1219

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DOI： 10.11316/jpsgaiyo.70.2.0_944

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Venue：大阪   Country：Japan  

DOI： 10.11316/jpsgaiyo.70.2.0_2509

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DOI： 10.11316/jpsgaiyo.70.2.0_2477

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Venue：大阪   Country：Japan  

DOI： 10.11316/jpsgaiyo.70.2.0_787

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Venue：大阪   Country：Japan  

DOI： 10.11316/jpsgaiyo.70.2.0_769

Event date： 2015.9

Language：Japanese   Presentation type：Poster presentation  

Venue：福岡   Country：Japan  

Event date： 2015.9

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Venue：大阪   Country：Japan  

DOI： 10.11316/jpsgaiyo.70.2.0_710

Event date： 2015.9

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Venue：愛知   Country：Japan  

Event date： 2015.9

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Venue：大阪   Country：Japan  

DOI： 10.11316/jpsgaiyo.70.2.0_879

Event date： 2015.7

Language：English   Presentation type：Poster presentation  

Venue：Barcelona   Country：Spain  

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Venue：東京   Country：Japan  

DOI： 10.11316/jpsgaiyo.70.1.0_1025

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛知   Country：Japan  

DOI： 10.11316/jpsgaiyo.69.2.3.0_298_1

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Language：Japanese   Presentation type：Poster presentation  

Venue：愛知   Country：Japan  

DOI： 10.11316/jpsgaiyo.69.2.3.0_280_4

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Venue：北海道   Country：Japan  

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Venue：愛知   Country：Japan  

DOI： 10.11316/jpsgaiyo.69.1.3.0_499_1

Event date： 2014.9

Language：Japanese   Presentation type：Poster presentation  

Venue：愛知   Country：Japan  

DOI： 10.11316/jpsgaiyo.69.2.4.0_691_4

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Language：Japanese   Presentation type：Poster presentation  

Venue：愛知   Country：Japan  

DOI： 10.11316/jpsgaiyo.69.2.3.0_297_4

Event date： 2014.4

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Venue：神奈川   Country：Japan  

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Venue：神奈川   Country：Japan  

Event date： 2014.3

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Venue：神奈川   Country：Japan  

DOI： 10.11316/jpsgaiyo.69.1.3.0_536_3

Event date： 2014.3

Language：Japanese   Presentation type：Poster presentation  

Venue：神奈川   Country：Japan  

DOI： 10.11316/jpsgaiyo.69.1.3.0_536_2

Event date： 2014.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：神奈川   Country：Japan  

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Venue：神奈川   Country：Japan  

Event date： 2014.3

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Venue：神奈川   Country：Japan  

DOI： 10.11316/jpsgaiyo.69.2.3.0_264_3

Event date： 2013.11

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Venue：長崎   Country：Japan  

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Event date： 2013.8

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Venue：東京   Country：Japan  

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Venue：東京   Country：Japan  

Event date： 2013.8

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Venue：東京   Country：Japan  

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Language：English   Presentation type：Oral presentation (general)  

Venue：千葉   Country：Japan  

Event date： 2013.7

Language：English   Presentation type：Poster presentation  

Venue：千葉   Country：Japan  

Event date： 2013.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

DOI： 10.11316/jpsgaiyo.68.1.3.0_547_2

Event date： 2013.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

DOI： 10.11316/jpsgaiyo.68.1.3.0_547_4

Event date： 2013.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

DOI： 10.11316/jpsgaiyo.68.1.3.0_512_1

Event date： 2013.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

Event date： 2013.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：神奈川   Country：Japan  

Event date： 2012.11

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：京都   Country：Japan  

Event date： 2012.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都   Country：Japan  

Event date： 2012.9

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：神奈川   Country：Japan  

DOI： 10.11316/jpsgaiyo.67.2.3.0_393_2

Event date： 2012.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：神奈川   Country：Japan  

Event date： 2012.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：神奈川   Country：Japan  

DOI： 10.11316/jpsgaiyo.67.2.3.0_428_2

Event date： 2012.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：神奈川   Country：Japan  

Event date： 2012.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：神奈川   Country：Japan  

DOI： 10.11316/jpsgaiyo.67.2.3.0_395_4

Event date： 2012.9

Language：English   Presentation type：Poster presentation  

Venue：神奈川   Country：Japan  

Event date： 2012.9

Language：English   Presentation type：Poster presentation  

Venue：神奈川   Country：Japan  

Event date： 2012.7

Language：English   Presentation type：Poster presentation  

Venue：Busan   Country：Korea, Republic of  

Event date： 2012.7

Language：English   Presentation type：Poster presentation  

Venue：Busan   Country：Korea, Republic of  

Event date： 2012.7

Language：English   Presentation type：Poster presentation  

Venue：Busan   Country：Korea, Republic of  

Event date： 2012.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：兵庫   Country：Japan  

DOI： 10.11316/jpsgaiyo.67.1.3.0_492_4

Event date： 2012.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：兵庫   Country：Japan  

DOI： 10.11316/jpsgaiyo.67.1.3.0_497_1

Event date： 2012.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：兵庫   Country：Japan  

DOI： 10.11316/jpsgaiyo.67.1.3.0_519_2

Event date： 2012.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：兵庫   Country：Japan  

DOI： 10.11316/jpsgaiyo.67.1.3.0_519_3

Event date： 2012.1

Language：Japanese   Presentation type：Poster presentation  

Venue：大阪   Country：Japan  

Event date： 2012.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪   Country：Japan  

Event date： 2011.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島   Country：Japan  

Event date： 2011.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島   Country：Japan  

Event date： 2011.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：富山   Country：Japan  

DOI： 10.11316/jpsgaiyo.66.2.3.0_423_3

Event date： 2011.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：富山   Country：Japan  

DOI： 10.11316/jpsgaiyo.66.2.3.0_423_2

Event date： 2011.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：富山   Country：Japan  

DOI： 10.11316/jpsgaiyo.66.2.3.0_414_3

Event date： 2011.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：富山   Country：Japan  

DOI： 10.11316/jpsgaiyo.66.2.3.0_407_2

Event date： 2011.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：富山   Country：Japan  

DOI： 10.11316/jpsgaiyo.66.2.3.0_400_3

Event date： 2011.9

Language：English   Presentation type：Poster presentation  

Venue：Bali   Country：Indonesia  

Event date： 2011.8

Language：English   Presentation type：Poster presentation  

Venue：Beijing   Country：China  

Event date： 2011.8

Language：English   Presentation type：Poster presentation  

Venue：Beijing   Country：China  

Event date： 2011.8

Language：English   Presentation type：Poster presentation  

Venue：Beijing   Country：China  

Event date： 2011.8

Language：English   Presentation type：Poster presentation  

Venue：Beijing   Country：China  

Event date： 2011.8

Language：English   Presentation type：Poster presentation  

Venue：Beijing   Country：China  

Event date： 2011.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：新潟   Country：Japan  

DOI： 10.11316/jpsgaiyo.66.1.3.0_462_2

Event date： 2011.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：新潟   Country：Japan  

DOI： 10.11316/jpsgaiyo.66.1.3.0_484_1

Event date： 2011.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：新潟   Country：Japan  

DOI： 10.11316/jpsgaiyo.66.1.3.0_507_2

Event date： 2011.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：新潟   Country：Japan  

Event date： 2011.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：新潟   Country：Japan  

DOI： 10.11316/jpsgaiyo.66.1.3.0_507_3

Event date： 2011.2

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2011.1

Language：English   Presentation type：Oral presentation (general)  

Venue：宮城   Country：Japan  

Event date： 2011.1

Language：English   Presentation type：Poster presentation  

Venue：宮城   Country：Japan  

Event date： 2011.1

Language：English   Presentation type：Poster presentation  

Venue：宮城   Country：Japan  

Event date： 2010.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：宮城   Country：Japan  

Event date： 2010.11

Language：Japanese   Presentation type：Poster presentation  

Venue：東京   Country：Japan  

Event date： 2010.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪   Country：Japan  

DOI： 10.11316/jpsgaiyo.65.2.3.0_365_1

Event date： 2010.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪   Country：Japan  

DOI： 10.11316/jpsgaiyo.65.2.3.0_444_1

Event date： 2010.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪   Country：Japan  

DOI： 10.11316/jpsgaiyo.65.2.3.0_418_2

Event date： 2010.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪   Country：Japan  

DOI： 10.11316/jpsgaiyo.65.2.3.0_405_3

Event date： 2010.9