Mössbauer spectroscopy studies on magnetic properties for⁵⁷Fe-substituted Ni-Mn-Sn metamagnetic shape memory alloys

In order to investigate the Fe substituted effects on the magnetic properties of the Ni-Mn-Sn metamagnetic shape memory alloys, magnetization and the Mössbauer spectroscopy measurements were carried out with using 57Fe-doped specimens of Ni₂Mn_1.48−x⁵⁷Fe_xSn_0.52 (x = 0.02, 0.04 and 0.08). Singlet-type Mössbauer spectra were clearly observed for x = 0.02 and 0.04 just below the martensitic transformation temperature, T_M, and above the Curie temperature, T_C, in the austenite phase. It was clear that the magnetic state in the martensite phase just below T_M was paramagnetic for x = 0.02 and 0.04. In further doped⁵⁷Fe to Ni₂Mn_1.48Sn_0.52, TC in the austenite phase slightly increased. However, the value of TM significantly decreased. As a result, martensite phase with small spontaneous magnetization directly transformed to the ferromagnetic austenite phase during heating for x = 0.08. These results obtained from the Mössbauer spectra were consistent with the results of the magnetic measurements in this study and the phase diagram reported by Fukushima et al. for normal Fe-doped Ni₂Mn_1.48−xFe_xSn_0.52 alloys. The breakdown of the general rule, in which the ferromagnetic shape memory alloys with larger value of the valence electrons per atom, e/a, showed higher TM, was also appeared in Ni₂Mn_1.48−xFe_xSn_0.52 alloys, being similar to Ni₂Mn_1−xFe_xGa alloys.