The Phase Transition And Magnetism Of The Mn-based Ferromagnetic Shape-memory Alloys

Functional material of Ni-Mn-X (X=In, Sn, or Sb) ferromagentic shape memory al-loy is hot recently because of underlying physics such as the giant magnetocaloric effect, magnetostricitve effect, magnetoresistance effect, and barocaloric effect. Based on these magnetic effects, the alloy will play its due roles in new concept refrigerator, sensor, and drivers. In this paper, we report some detailed studies on the Mn-based alloys of Mn5oNi41Sn9(Fe-doped), Mn5oNi49Sn and Mn5oNi49ln:1. The influence of Fe doping on the phase transitions, magnetocaloric effect, and ex-change bias in Mn50Ni41-xFexSn9 alloys.Mn50Ni41-xFexSn9 (x=0,2,4) alloys were prepared by the arc melting method. The crystal structure, phase transition, magnetocaloric effect, and exchange bias were investi-gated by X-ray diffraction (XRD), physical property measurement system (PPMS), and vi-brating sample magnetometer (VSM). It’s elucidated that the martensitic transformation tem-perature will decrease with increased content of Fe, while the Curie temperature of the martensitic or austenitic phase increases gradually. And the doped Fe leads to the increase in the magnetization change across the martensitic transformation, which gives rise to relatively large magnetocaloric effect. Furthermore, the exchange bias field will decrease with the in-creasing Fe concentration, because the doping of Fe can enhance the ferromagnetic interac-tion in the alloy.2. The magnetism of the Mn50Ni49X (X=Sn, In) ribbonsThe Mn5oNi49X (X=Sn, In) ribbons with an average grain size of 3 um were pre-pared by the melt-spinning technique. Mn50Ni41Sn9 exhibits spin glass behavior at low tem-perature, and shows large zero-field cooled exchange-bias. When the magnetic field is larger than the critical field, there is the zero-field cooled exchange-bias (very sensitive to maxi-mum magnetic field), and this indicates the formation of unidirectional anisotropy during the initial magnetization process. It’s found that the exchange-bias field as well as the coercivity decrease with increasing temperature. By contrast, the Mn50Ni41In9 alloy does not exhibit spin glass property at low temperature, and its field cooled exchange-bias is very small and shows no zero-field cooled exchange-bias effect.