Language：English   Publisher：The Japan Institute of Metals and Materials  

<p>Magnetic and structural properties of MnCo₁₋<i>_x</i>Fe<i>_x</i>Ge₁₋<i>_y</i>Si<i>_y</i> (<i>x</i>, <i>y</i> = 0, 0.5) were investigated using X-ray powder diffraction and magnetization measurements in the temperature (<i>T</i>) range from 5 to 370 K and in magnetic fields up to μ₀<i>H</i> = 5 T. At room temperature, MnCoGe and MnCoGe_0.5Si_0.5 were the orthorhombic crystal structure (M-phase), MnCo_0.5Fe_0.5Ge was the hexagonal crystal structure (P-phase), and MnCo_0.5Fe_0.5Ge_0.5Si_0.5 had two-phase coexistence of the M- and P-phases. MnCoGe and MnCo_0.5Fe_0.5Ge were a simple ferromagnetic and their Curie temperatures (<i>T</i>_C) were determined to be 340 K and 200 K, respectively. MnCoGe_0.5Si_0.5 and MnCo_0.5Fe_0.5Ge_0.5Si_0.5 in μ₀<i>H</i> ≤ 1 T showed a gentle dip in thermomagnetic curves at 10 ≤ <i>T</i> ≤ 100 K below <i>T</i>_C which disappears when a magnetic field of μ₀<i>H</i> > 3 T was applied. The magnetization curves of MnCoGe_0.5Si_0.5 and MnCo_0.5Fe_0.5Ge_0.5Si_0.5 at 5 K exhibited that a metamagnetic transition with the magnetic hysteresis in 0 < μ₀<i>H</i> < 3 T. Our results suggest that substituting Fe for Co in MnCoGe system weakens the ferromagnetic interaction, whereas substituting Si for Ge strengthens the antiferromagnetic interaction.</p>

DOI： 10.2320/matertrans.mt-mbw2024001

CiNii Research

Language：Japanese   Publisher：Interactions  

X-ray powder diffraction, magnetization, and 57Fe Mössbauer spectroscopy measurements were performed to investigate the effects of heat treatment on the magnetic properties of MnFeGe with hexagonal Ni2In-type structure. The samples were annealed at 1173 K for 24 h, as a solution treatment (ST), and then aged at 1073 K (AG-1073 K), 973 K (AG-973 K) and 773 K (AG-773 K). Curie temperature was the highest at AG-1073 K (201 K), and the lowest at AG-773 K (169 K). In ST and AG-1073 K, Mössbauer spectrum was represented by three subspectra. In AG-1073 K, 19% of the Fe atoms occupied 2a-site and 71% of the Fe atoms occupied 2d-site. The hyperfine fields of 2a- and 2d-sites at 15 K were 20.3 T and 9.99 T, respectively. Approximately 10% of the iron atoms contributed to the subspectrum of nonmagnetic phase. On the other hand, to represent the spectra obtained at 15 K for samples annealed at lower temperatures (AG-973 K and AG-773 K), an additional subspectrum with the hyperfine field of 21.6–22.0 T was required, which was due to the ferromagnetic impurity phase. The obtained results showed that as the aging temperature decreased, Fe occupying the 2a-site with a large hyperfine field decreased, resulting in a decrease in the macroscopic magnetic properties of MnFeGe.

DOI： 10.1007/s10751-024-01951-9

Scopus

Language：Japanese   Publisher：Interactions  

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

Scopus

Language：Japanese   Publisher：Interactions  

In order to clarify the influence of the magnetic field on the thermal decomposition of Sm2Fe17N3 powder, we conducted a heat-treatment (HT) experiment in a vacuum of 38 Pa, at a temperature of 723 K, and in a magnetic field of zero and 5 T. Results of X-ray diffraction measurement, temperature dependence of magnetization and 57Fe Mössbauer spectroscopy experiments showed that fully-nitride Sm2Fe17N3 decomposes to nitrogen-poor Sm2Fe17Nx (0 < x < 3), α-Fe, Fe2O3 and Fe3O4. The magnetic field promoted the thermal decomposition of Sm2Fe17N3 in this HT condition.

DOI： 10.1007/s10751-024-01942-w

Scopus

Language：Japanese   Publisher：Interactions  

High magnetic field effects on the phase separation of Fe-rich and Cu-rich phases in Fe-15mass%Cu were investigated using microstructural observation and 57Fe Mössbauer spectroscopy. Fe-15mass%Cu annealing was carried out at 773 K with or without a 5 T magnetic field. Microstructural observations showed that the Fe-rich grains were separated by a Cu-rich phase, and the width of the Cu-rich phase for the samples annealed at 5 T tended to be narrower than that of the samples annealed at 0 T. The Mössbauer spectrum of the samples measured at room temperature is represented by two sub-spectra. The hyperfine fields Bhf of the two sub-spectra were 33.0–33.1 T and 31.4–31.7 T and they did not change with annealing time or the presence of a magnetic field. The spectrum with a higher (lower) Bhf corresponded to the centre (near the grain boundary) of the Fe-rich grain. The occupancy of the spectrum with a lower Bhf for the sample annealed at 5 T was larger than that for the sample annealed at 0 T by up to 5%. This indicated that the change of Cu concentration at the grain boundary became gentle. Therefore, the high magnetic field effects were coarsening of the Fe-rich grains and a gentle change in the Cu concentration at the grain boundary.

DOI： 10.1007/s10751-024-01939-5

Scopus

Language：Japanese