Study of heat treatment effect on magnetic properties of MnFeGe using ⁵⁷Fe Mössbauer spectroscopy

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.