Faculty Profiles - SHIGETA Iduru

Papers - SHIGETA Iduru

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Hideki Aoshima, Iduru Shigeta, Akiko Nomura, Kunio Yubuta, Touru Yamauchi, Rie Y. Umetsu, Takeshi Kanomata, Masahiko Hiroi . The critical behavior of magnetization near the Curie temperature in highly spin-polarized Heusler alloy Co<sub>2</sub>TiGa<sub>0.3</sub>Sn<sub>0.7</sub> . IEEE Transactions on Magnetics60 ( 9 ) 4100305-1 - 4100305-5 2024.9Reviewed International journal

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal)

We present an analysis of the critical behavior of magnetization near the Curie temperature <italic>T</italic><sub>C</sub> in Heusler alloy Co<sub>2</sub>TiGa<sub>0.3</sub>Sn<sub>0.7</sub>, which is a promising candidate for highly spin-polarized materials that exhibit the characteristic properties of magnetic Weyl states. Weyl semimetals have garnered significant interest for their potential applications in spintronics devices, owing to their anomalous magnetoelectronic and magnetothermal properties. The magnetization of the synthesized Heusler alloy Co<sub>2</sub>TiGa<sub>0.3</sub>Sn<sub>0.7</sub> was investigated in the vicinity of <italic>T</italic><sub>C</sub>. The analysis of magnetic isotherms for Co<sub>2</sub>TiGa<sub>0.3</sub>Sn<sub>0.7</sub> reveals that the critical exponent δ is deduced to be 5.16 in the high field region and 4.96 in the low field region. The obtained value of δ deviates from the value of 3.0 expected by the conventional molecular field theory. However, it is in close agreement with the value of 5.0 predicted by the spin fluctuation theory for weak itinerant electron ferromagnets, exhibiting that the spin fluctuation theory is applicable even to highly spin-polarized Heusler alloys.

DOI： 10.1109/TMAG.2024.3414430

Hideki Aoshima, Iduru Shigeta, Akiko Nomura, Kunio Yubuta, Touru Yamauchi, Rie Y. Umetsu, Takeshi Kanomata, Masahiko Hiroi . The critical behavior of magnetization near the Curie temperature in highly spin-polarized Heusler alloy Co<sub>2</sub>TiGa<sub>0.3</sub>Sn<sub>0.7</sub> . 2024 IEEE International Magnetic Conference Proceedings - INTERMAG 2024 Short Papers 1 - 2 2024.5Reviewed

Masahiko Hiroi, Tsubasa Takamoto, Iduru Shigeta, Masahira Onoue . Mössbauer study of magnetically ordered states in Heusler compounds Fe<sub>3−</sub><i><sub>x</sub></i>Mn<i><sub>x</sub></i>Si . Interactions245 ( 1 ) 58-1 - 58-9 2024.4Reviewed International journal

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

It has been known that the Heusler compound Fe3-xMnxSi has a complex magnetic phase diagram. For 0.75 ≤x≤ 1.75, it exhibits a ferromagnetic transition at TC, and at a lower temperature TA, another transition to a phase with both ferromagnetic and antiferromagnetic components. Recently, however, magnetization and specific heat measurements revealed that for x= 1.7, yet another transition occurs at a temperature lower than TA, i.e., there are three transitions at zero magnetic field. In our previous study, the nature of the ordered phases and transitions for x= 1.7 and 1.68 were investigated using Mössbauer spectroscopy, and the existence of a hyperfine field Bhf was confirmed. This demonstrates that the low temperature phases are magnetically ordered phases. In this study, to further investigate the ordered phases and transitions in Fe3-xMnxSi, we measure Mössbauer spectra for x = 1.8 and 1.9, where only a single antiferromagnetic transition appears to exist as judged from magnetization measurements, and the transition temperature is defined as TA2′. The spectra show that Bhf is present for x= 1.8 and 1.9 at low temperatures, and the values of Bhf are comparable with that for x = 1.7. With increasing temperature T, Bhf decreases smoothly, and at T>TA2′ the spectrum becomes a singlet and Bhf is zero. These results confirm the existence of magnetic order for x = 1.8 and 1.9.

DOI： 10.1007/s10751-024-01903-3

Masahiko Hiroi, Kouki Akaishi, Tomohito Nonoyama, Iduru Shigeta, d Masahira, Onoue . Mössbauer Spectroscopy of Magnetic Ordered Phases in Heusler Compounds Fe3−xMnxSi . JPS Conference Proceedings38 011136-1 - 011136-6 2023.5Reviewed International journal

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

For 0.75 ≤ x ≤ 1.75, the Heusler compound Fe3−xMnxSi undergoes two phase transitions: one ferromagnetic at TC and another to a phase with antiferromagnetic properties at a lower temperature, TA. It was recently discovered that for x = 1.7, another antiferromagnetic transition occurs at a temperature even lower than TA, TA2. In addition, the phase below TA2 is defined as the AF2 phase. In this study, Mössbauer spectroscopy measurements were performed for samples with x = 1.5, 1.68, and 1.7 down to ∼10 K to explore the properties of these magnetically ordered phases. At high temperatures, a singlet peak was observed and no hyperfine field was detected. At low temperatures the peak became broader, reflecting the increase in the hyperfine field in the magnetically ordered phases. For x = 1.7 and 1.68, the hyperfine field increased smoothly with decreasing temperature from TC through TA and TA2 to low temperatures. TC estimated via the temperature dependence of the hyperfine field agrees with the results of the magnetization measurements. These findings show that despite the small macroscopic magnetization below TA2, an internal field exists, implying that the AF2 phase is an antiferromagnetic ordered phase.

DOI： 10.7566/JPSCP.38.011136

Hideki Aoshima, Iduru Shigeta, Jun Gouchi, Touru Yamauchi, Takeshi Kanomata, Rie Y. Umetsu, Yoshiya Uwatoko, Shinpei Fujii, Masahiko Hiroi . Magnetic properties of highly spin-polarized Heusler alloy CoFeCrAl . JPS Conference Proceedings38 011133-1 - 011133-6 2023.5Reviewed International journal

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

We report the magnetic properties of quaternary Heusler alloy CoFeCrAl as a potential candidate for spin-gapless semiconductor (SGS). The obtained magnetization of CoFeCrAl showed that the spontaneous magnetization Mexps was 2.021 μB/f.u., Mexps was independent of applying pressure, and the high magnetic field susceptibility χexphf was almost independent of magnetic fields. We have further investigated the electronic structure by the first-principles band calculations. The total density of states (DOS) demonstrated typical SGS-like structure, and thus the spin polarization Pcal was deduced to be 95.47% at the Fermi energy EF and the total magnetic moment Mcaltot is 1.999 μB/f.u., respectively. We found that Mexps is good agreement with Mcaltot following the Slater–Pauling rule. Therefore, we conclude that CoFeCrAl is a highly spin-polarized material and it is suitable for applying to counterelectrodes in spintronic devices.

DOI： 10.7566/JPSCP.38.011133

Kouki Akaishi, Iduru Shigeta, Masahiko Hiroi, Jun Gouchi, Yoshiya Uwatoko . Effect of pressure on the magnetic properties of Heusler compound Fe<sub>1.3</sub>Mn<sub>1.7</sub>Si . JPS Conference Proceedings38 011135-1 - 011135-6 2023.5Reviewed International journal

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

The Heusler compound Fe3−xMnxSi has been studied in various compositions and it exhibits complex magnetic properties at low temperatures. In ambient pressure at zero field, when x = 1.7, particularly, it orders ferromagnetically below TC ≈ 85 K, exhibits a transition to a phase with antiferromagnetic components at TA ≈ 67 K; furthermore, it orders antiferromagnetically at an even lower temperature of TA2 ≈ 60 K. For the dependence on the magnetic field of these transition temperatures, TA(B) and TA2(B), with increasing magnetic field, TA(B) changes only slightly, whereas TA2(B) shifts toward lower temperatures. In this study, magnetization measurements under pressures up to 1.2 GPa were performed to investigate pressure effects on transition temperatures and magnetic fields. The B–T magnetic phase diagram is presented, which summarizes the transition temperatures and magnetic fields obtained from these results. With increasing applied pressure, the TA2(B) line shows a shift toward the higher magnetic fields and temperatures, whereas TA(B) changes only slightly, and TC decreases and disappears around ∼1 GPa.

DOI： 10.7566/JPSCP.38.011135

Iduru Shigeta, Shuta Oku, Takahide Kubota, Shojiro Kimura, Takeshi Seki, Bunju Shinozaki, Satoshi Awaji, Koki Takanashi, Masahiko Hiroi . Superconducting fluctuation effect on epitaxially layered films of superconductor NbN and half-metallic Heusler alloy Co<sub>2</sub>MnSi . AIP Advances13 025116-1 - 025116 -5 2023.2Superconducting fluctuation effect on epitaxially layered films of superconductor NbN and half-metallic Heusler alloy Co<sub>2</sub>MnSiReviewed International journal

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

Superconducting properties were investigated in epitaxially layered films consisting of superconductor NbN and half-metallic Heusler alloy Co2MnSi (CMS). Temperature dependence of the electrical resistivity ρ(T) was measured by applying perpendicular magnetic fields to the surface of NbN/CMS films. With the increase of the CMS thickness dCMS, the upper critical field μ0Hc2 decreased monotonically, but the superconducting transition temperature Tc had the minimum of 10.1 K at dCMS ≈ 5 nm. The Tc behavior was in qualitative agreement with the theory of the π-coupling. The pair-breaking parameter δ determined by the superconducting fluctuation theory took the maximum at dCMS = 3 ∼5 nm, which would be related to the minimum of Tc. The experimental results reveal that the superconductivity of the NbN layer in NbN/CMS films is affected by the interplay between the superconducting NbN layer and the half-metallic CMS layer.

DOI： 10.1063/9.0000584

T. Kanomata, Y. Amako, Y. Ida, Y. Adachi, T. Osaki, T. Eto, H. Nishihara, I. Shigeta, S. Imada, M. Doi . Magnetic properties of ferromagnetic Heusler alloy Co<sub>2</sub>ZrSn . Journal of Physics and Chemistry of Solids164 110635-1 - 110635-7 2022.5Magnetic properties of ferromagnetic Heusler alloy Co<sub>2</sub>ZrSnReviewed International journal

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

The results of experimental investigations of the crystal structure, permeability, magnetization and Mössbauer spectroscopy of Co2ZrSn are reported. The sample, which was prepared by arc melting, comprised of a Heusler structure Co2ZrSn that coexisted with a small amount of an impurity phase. The Curie temperature TC of Co2ZrSn was found to be 452.3 K. At 1.8 K the magnetic moment of Co2ZrSn was estimated to be 2.0 μB/f.u., confirming that the magnetic moment of Co2ZrSn obeys the Slater-Pauling rule. The temperature variation of the spontaneous magnetization Ms roughly follows the Brillouin function for spin value S = 1/2. However, in the temperature region of T/TC > 0.6, Ms is distinctly higher than the Brillouin function. The TC of Co2ZrSn was almost independent of pressure. The Mössbauer spectroscopy measurements showed that the isomer shift I.S. (1.5 mm/s at 295 K) was approximately temperature independent. At 95 K the value of the hyperfine magnetic field HhfSn at the Sn nuclei was found to be 101 kOe. The temperature variation of HhfSn of Co2ZrSn roughly followed the Brillouin function for S = 1/2. On the basis of the experimental results, the electronic and magnetic properties of Co2ZrSn are discussed.

DOI： 10.1016/j.jpcs.2022.110635

Soichiro Tsujikawa, Iduru Shigeta, Jun Gouchi, Takeshi Kanomata, Rie Y. Umetsu, Yoshiya Uwatoko, Masahiko Hiroi . Magnetization of Quaternary Heusler Alloy CoFeCrAl . IEEE Transactions on Magnetics58 ( 2 ) 2600505-1 - 2600505-5 2022.2Magnetization of Quaternary Heusler Alloy CoFeCrAlReviewed International journal

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal)

We report the magnetovolume effect of quaternary Heusler alloy CoFeCrAl as a potential candidate of spin gapless semiconductor. The crystal structure of CoFeCrAl was confirmed as the single phase of the ordered LiMgPdSn-type structure. From magnetization measurements at ambient pressure, the Curie temperature TC and the spontaneous magnetization Ms were determined to be 575.2 K and 2.01 μ B/f.u., respectively. The TC is higher enough than room temperature and the Ms follows the Slater-Pauling rule. High-pressure magnetization measurements showed that the Ms is almost independent of applying pressures not only at 10 K but also up to 300 K, exhibiting that the electronic state of CoFeCrAl is fully spin polarized and it is preserved even at 300 K. The experimental results reveal that the quaternary Heusler alloy CoFeCrAl is an attractive material for functional electrode ferromagnets in spintronics devices.

DOI： 10.1109/TMAG.2021.3096227

Takaaki Yokoyama, Iduru Shigeta, Akiko Nomura, Kunio Yubuta, Touru Yamauchi, Rie Y. Umetsu, Hironori Nishihara, Takeshi Kanomata, Masahiko Hiroi . Critical Behavior of the Magnetization in Heusler Alloy Co2TiGa0.8Sn0.2 . IEEE Transactions on Magnetics58 ( 2 ) 2600404-1 - 2600404-4 2022.2Critical Behavior of the Magnetization in Heusler Alloy Co2TiGa0.8Sn0.2Reviewed International journal

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

We report the critical behavior of the magnetization in Heusler alloy Co2TiGa0.8Sn0.2 as a potential candidate of high spin polarized materials with the characteristics of topological Weyl fermions. The Weyl semimetals are materials of great interest for applying spintronics devices, due to their unusual magnetoelectronic and magnetothermal properties. The magnetic properties of the synthesized Heusler alloy Co2TiGa0.8Sn0.2 are investigated around the Curie temperature TC. The magnetic isotherm measurements of Co2TiGa0.8Sn0.2 around TC exhibit that the critical exponent δ is deduced to be 4.455(4) in high maximum applied field of 50 kOe and 4.823(9) in low maximum applied field of 10 kOe, respectively. Both δ values are different from 3.0 derived by the conventional molecular field theory, but they are close to 5.0 predicted by the spin fluctuation theory for the itinerant electron ferromagnets. Possible origins for the discrepancy between experimental results and theoretical models are also discussed.

DOI： 10.1109/TMAG.2021.3097164

Hiroi Masahiko, Nonoyama Tomohito, Shigeta Iduru, Yamauchi Touru . Multiple Magnetic Phase Transitions in Fe3−xMnxSi Heusler Compounds . Journal of the Physical Society of Japan90 ( 10 ) 103701-1 - 103701-5 2021.10Reviewed International journal

Masahiko Hiroi, Tomohito Nonoyama, Iduru Shigeta, Touru Yamauchi . Multiple magnetic phase transitions in Fe<sub>3−x</sub>Mn<sub>x</sub>Si Heusler compounds . Journal of the Physical Society of Japan90 ( 10 ) 103701-1 - 103701-5 2021.10Multiple magnetic phase transitions in Fe<sub>3−x</sub>Mn<sub>x</sub>Si Heusler compoundsReviewed International journal

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

Fe3−xMnxSi (x > 0.75) exhibits a ferromagnetic transition at TC and a transition to an antiferromagnetic phase with a ferromagnetic component at a temperature (TA) lower than TC, defined as the AF phase. Recently, in Fe1.3Mn1.7Si, another magnetic transition at a temperature lower than TA, defined as TA2, was observed. The phase below TA2 is referred to as the AF2 phase and is likely antiferromagnetic. This paper presents evidence for multiple phase transitions in Fe1.3Mn1.7Si obtained from specific heat and magnetization measurements. In addition, the magnetic transitions and magnetic properties of Fe3−xMnxSi (1.65 ≤ x ≤ 1.8) are investigated.

DOI： 10.7566/JPSJ.90.103701

Masahiko Hiroi, Sora Nishiinoue, Iduru Shigeta, Masakazu Ito, Keiichi Koyama, Akihiro Kondo, Koichi Kindo, Isao Watanabe, Muneaki Fujii, Shojiro Kimura, Hirotaka Manaka, Norio Terada . High magnetic field properties in Ru$_{2-x}$Fe$_{x}$CrSi with antiferromagnetic and spin-glass states . Physical Review B103 ( 9 ) 094428-1 - 094428-12 2021.3High magnetic field properties in Ru$_{2-x}$Fe$_{x}$CrSi with antiferromagnetic and spin-glass statesReviewed International journal

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

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

Tomohito Nonoyama, Ryota Kato, Iduru Shigeta, Masahiko Hiroi, Hirotaka Manaka, Norio Terada . Magnetic transition in the Heusler compounds Fe$_{3- x}$Mn$_{x}$Si . AIP Advances8 ( 11 ) 115018-1 - 115018-5 2018.11Reviewed International journal

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

It has been shown that Fe MnSi exhibits a ferromagnetic transition at Tc and an antiferromagnetic transition at a lower temperature, T , to a phase referred to as the AF phase. In a recent study on Fe Mn Si, another antiferromagnetic transition at a temperature lower than T , defined as T , was found, with the phase below T referred to as the AF2 phase. In this study, magnetic properties of Fe Mn Si 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 T 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 T 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. 2 A 1.3 1.7 A A2 A2 3-x x A A2

DOI： 10.1063/1.5080429

Ryota Kato, Tomohito Nonoyama, Ryutaro Ooka, Iduru Shigeta, Masahiko Hiroi . Transport properties of Heusler compounds Fe$_{3- x}$Mn$_{x}$Si ($x$ = 1.6, 1.7 and 1.8) under magnetic fields . AIP Advances8 ( 11 ) 115019-1 - 115019-4 2018.11Reviewed International journal

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

Measurements of the electrical resistivity, magnetoresistance (MR), and Hall effects are performed to investigate the transport properties of Fe Mn Si (x = 1.6, 1.7, and 1.8) under magnetic fields. It is known that Fe MnSi exhibits a ferromagnetic transition at T and an antiferromagnetic transition at a lower temperature (T ) to the phase referred to as the AF phase. A recent study on Fe Mn Si found another antiferromagnetic transition at a temperature below T , defined as T , to a phase referred to as the AF2 phase. In this study, in MR measurements for x = 1.7 and 1.8, the change in MR with magnetic field is found to transition from positive to negative at certain magnetic fields. Comparing these results with those of magnetization measurements, these points correspond to the AF2-AF transitions. The results also indicate that these transitions occur at a higher field for x = 1.8 than for x = 1.7. The Hall effect measurements show the anomalous Hall effect for x = 1.6 and 1.7 in the temperature region where spontaneous magnetization is present, but not for x = 1.8, for which the ferromagnetic state appears to be absent. These results are consistent with the magnetization measurements. 3-x x 2 C A 1.3 1.7 A A2

DOI： 10.1063/1.5043075

Iduru Shigeta, Takahide Kubota, Yuya Sakuraba, Shojiro Kimura, Satoshi Awaji, Koki Takanashi, Masahiko Hiroi . Transport properties of epitaxial films for superconductor NbN and half-metallic Heusler alloy Co2MnSi under high magnetic fields . Physica B: Condensed Matter536 310 - 313 2018.5Reviewed International journal

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

Transport properties were investigated for epitaxial films of superconductor NbN and half-metallic Heusler alloy Co2MnSi under high magnetic fields up to 17 T. The superconducting transition temperature Tc of NbN/Co2MnSi/Au trilayer films was determined to be 16.1K in the absence of magnetic field. Temperature dependence of the resistivity ρ(T) was measured in both magnetic fields parallel and perpendicular to the surface of NbN/Co2MnSi/Au trilayer films. The activation energy U0(H) for vortex motion of the trilayer films in both magnetic fields was well fitted above 5 T by the similar model with the exponents in the field dependence of the pinning force density. From the resistivity ρ(T) measurements under high magnetic fields, the upper critical field Hc2(0) at 0 K was also deduced to be μ0Hc2 ∥(0)=23.2T for the parallel magnetic filed and μ0Hc2 ⊥(0)=15.8T for the perpendicular magnetic field, respectively. The experimental results under magnetic fields revealed the superconductivity of the NbN layer was affected by the interplay between the superconducting NbN layer and the half-metallic Co2MnSi layer.

DOI： 10.1016/j.physb.2017.09.074

Ryutaro Ooka, Iduru Shigeta, Rie Y. Umetsu, Akiko Nomura, Kunio Yubuta, Touru Yamauchi, Takeshi Kanomata, Masahiko Hiroi . Temperature dependence of differential conductance in Co-based Heusler alloy Co2TiSn and superconductor Pb junctions . Physica B: Condensed Matter536 289 - 292 2018.5Reviewed International journal

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

We investigated temperature dependence of differential conductance G(V) in planar junctions consisting of Co-based Heusler alloy Co2TiSn and superconductor Pb. Ferromagnetic Co2TiSn was predicted to be half-metal by first-principles band calculations. The spin polarization P of Co2TiSn was deduced to be 60.0% at 1.4K by the Andreev reflection spectroscopy. The G(V) spectral shape was smeared gradually with increasing temperature and its structure was disappeared above the superconducting transition temperature Tc. Theoretical model analysis revealed that the superconducting energy gap Δ was 1.06meV at 1.4K and the Tc was 6.8K, indicating that both values were suppressed from bulk values. However, the temperature dependent Δ(T) behavior was in good agreement with that of the Bardeen-Cooper-Schrieffer (BCS) theory. The experimental results exhibit that the superconductivity of Pb attached to half-metallic Co2TiSn was kept the conventional BCS mechanism characterized strong-coupling superconductors while its superconductivity was slightly suppressed by the superconducting proximity effect at the Co2TiSn/Pb interface.

DOI： 10.1016/j.physb.2017.10.055

Masahiko Hiroi, Tomohito Nonoyama, Genta Adachi, Iduru Shigeta, Hirotaka Manaka, Norio Terada . Magnetic properties of Heusler compound Fe1.3Mn1.7Si . Journal of Physics: Conference Series969 ( 1 ) 012098-1 - 012098-6 2018.4Reviewed International journal

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Institute of Physics Publishing

The magnetic properties of two Heusler compounds Fe1.3Mn1.7Si and Fe1.4Mn1.6Si are compared. Fe1.4Mn1.6Si exhibits a ferromagnetic transition at TC ∼ 117 K and another transition to a phase with antiferromagnetic components at TA ∼ 66 K, which is the same as the behavior of Fe2MnSi. Further, it is known that for Fe3-xMn x Si, with increasing x, TC decreases but TA remains almost constant, and they appear to meet around x ∼1.7. The careful measurements of magnetization at various magnetic fields reveal that Fe1.3Mn1.7Si has three transitions at low fields
for instance, at 0.01 T, the transition temperatures are found to be 85 K, 67 K, and 60 K. The lowest transition at 60 K is characterized by a rapid decrease in magnetization with decreasing temperature and significant magnetic field dependence, in contrast to the transition at TA , which is relatively independent of the magnetic field, for x = 1 and 1.6. The critical field at 0 K is ∼3 T. The transition at the lowest temperature was not found for x ≤ 1.6, and it is considered a different transition from that at TA . While the transition at the highest temperature 85 K is a ferromagnetic transition, the transition at 67 K has the characteristics of the transition at TA , and it is found to be insensitive to magnetic fields. They are revealed to be the same transitions as those at TC and TA for x ≤ 1.6.

DOI： 10.1088/1742-6596/969/1/012098

Masahiko Hiroi, Syunya Ishikuma, Iduru Shigeta, Keiichi Koyama, Akihiro Kondo, Koichi Kindo, Hirotaka Manaka, Norio Terada . Magnetization and magnetic phase diagram of Heusler compounds Fe3-y(Mn1-xV x ) y Si (y = 1 and 1.5) . Journal of Physics: Conference Series969 ( 1 ) 012099-1 - 012099-6 2018.4Reviewed International journal

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Institute of Physics Publishing

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

Iduru Shigeta, Yutaro Fujimoto, Ryutaro Ooka, Yuya Nishisako, Masahito Tsujikawa, Rie Y. Umetsu, Akiko Nomura, Kunio Yubuta, Yoshio Miura, Takeshi Kanomata, Masafumi Shirai, Jun Gouchi, Yoshiya Uwatoko, Masahiko Hiroi . Pressure effect on the magnetic properties of the half-metallic Heusler alloy Co2TiSn . Physical Review B97 ( 10 ) 104414-1 - 104414-8 2018.3Reviewed International journal

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

Precise magnetization measurements of a half-metallic ferromagnet Co2TiSn with the Heusler type structure have been carried out under pressure up to 1.27 GPa. At ambient pressure, the spontaneous magnetic moment Msexp and the Curie temperature TCexp are experimentally obtained to be 1.993(3)μB/f.u. and 376.76(7) K, respectively. The Msexp is independent of applying pressure. The TCexp decreases with the increase of pressure and the pressure derivative of the Curie temperature dTCexp/dp is estimated to be -3.15(9) K/GPa. Furthermore, the pressure effect on the electronic and magnetic properties of Co2TiSn has been theoretically investigated on the basis of first-principles density functional calculations by using the projector augmented wave method in order to evaluate the half metallicity of Co2TiSn. Both the experimental and the theoretical results under pressure reveal that Co2TiSn is half metal. The experimental results of pressure-dependent magnetic properties are finally discussed on the basis of the spin fluctuation theory for itinerant electron magnetism.

DOI： 10.1103/PhysRevB.97.104414

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