Magnetic properties and martensitic transformation of Ni–Mn–Ge Heusler alloys from first-principles and Monte Carlo studies

Abstract

In the present study, the magnetic properties and possibility of martensitic transformation in a series of off-stoichiometric Ni2+xMn1−xGe and Ni2Mn1+xGe1−x Heusler alloys have been studied by using both first-principles and Monte Carlo methods. It is shown that in both cases an increase in chemical disorder stimulates the austenite–martensite transformation and leads to an increase in transition temperature. Moreover, the calculated formation energies confirm that these compounds are stable chemically. By using the exchange coupling constants obtained from ab initio calculations in combination with the Heisenberg model and Monte Carlo methods, the temperature-dependent magnetizations as well as Curie temperatures of the cubic and tetragonal Ni2+xMn1−xGe and Ni2Mn1+xGe1−x have been determined. The phase diagrams of alloys studied showing the compositions with magnetostructural transformation are obtained. Calculated results demonstrate a similar trend to the previous experimental and theoretic results for Ni–Mn–(Ga, In, Sn, Sb) alloys that makes them possible promising magnetic materials in technological applications.