Role of Magnetism in Lattice Instability and Martensitic Transformation of Heusler Alloys

Abstract

Heusler alloys are subject of considerable interest because they exhibit a martensitic transformation (MT), a shape-memory effect and a giant magnetocaloric effect. As it is commonly believed, the pronounced magnetoelastic coupling plays a crucial role; however, the effect of alloy composition on MT is still under discussion. To describe the features of MT in Ni0.75−xMnxGa0.25 Heusler alloys, the phenomenological model that consistently considers the magnetic and lattice degrees of freedom and their mutual interplay has been developed. The magnetic entropy contribution was estimated within the framework of the microscopic approach. The proposed model allows us to describe the dependence of the martensitic transformation start temperature Ms(x) on the Mn concentration x in reasonable agreement with the experiment.