Martensitic Transformations of Ni-Mn-X Heusler Alloys with X = Ga, In and Sn

摘要

Martensitic transformations of rapidly quenched and less rapidly cooled Heusler alloys of type Ni-Mn-X with X = Ga, In and Sn are investigated by ab initio calculations. For the rapidly cooled alloys, we obtain the magnetocaloric properties near the magnetocaloric transition. For the less rapidly quenched alloys these magnetocaloric properties start to change considerably. This shows that none of the Heulser alloys is in thermal equilibrium. Instead, each alloy transforms during temper-annealing into a dual-phase composite alloy. The two phases are identified to be cubic Ni-Mn-X and tetragonal NiMn.