Decomposition in Mn50Ni40In10 melt-spun ribbons and its influence on magnetic properties

Abstract

The phase stability, decomposition and its influence on the martensitic transformation and magnetic properties of magnetic shape memory alloy (MSMA) Mn50Ni40In10 melt-spun ribbons were investigated experimentally and theoretically. As-spun Mn50Ni40In10 was fine single Heusler phase with pronounced martensitic and magnetic transition below room temperature. However, in differential scanning calorimetry measurement an exothermic peak at 690 K and an endothermic peak at 765 K is observed during the heating of as-spun ribbons. The two peaks correspond to the growing of the punctiform precipitates in the grain interiors and the formation of a large amount of grain boundary segregation, respectively. After annealing at 870 K, the ribbon samples decompose into a cubic In-rich phase at grain boundaries and In-poor 7 M−modulate martensitic phase in the matrix. After annealing at 690 K and above, the martensitic transformation below room temperature is strongly weakened. Annealing temperature also has obvious influence on the 5 and 300 K saturation magnetization Ms of Mn50Ni40In10. Theoretical calculations on Mn2Ni1.5In0.5 (Mn50Ni37.5In12.5) give a negative formation energy (-0.11 eV/ f.u.) and a positive decomposition energy (0.22 eV/f.u.), indicating that this alloy can be metastable and tends to decompose into Mn2NiIn cubic phase and NiMn martensite, agreeing with the experimental results qualitatively.