Mössbauer Spectroscopy Studies on Magnetic Properties for 57Fe-substituted Ni-Mn-Sn Metamagnetic Shape Memory Alloys

Abstract

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 Ni2Mn1.48−x57FexSn0.52 (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, TM, and above the Curie temperature, TC, in the austenite phase. It was clear that the magnetic state in the martensite phase just below TM was paramagnetic for x = 0.02 and 0.04. In further doped 57Fe to Ni2Mn1.48Sn0.52, 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 Ni2Mn1.48−xFexSn0.52 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 Ni2Mn1.48−xFexSn0.52 alloys, being similar to Ni2Mn1−xFexGa alloys.

Keywords

• metamagnetic shape memory alloy
• mössbauer spectroscopy
• heusler alloy
• martensitic transformation
• austenite phase