First-principles study of exchange interactions and Curie temperatures of half-metallic ferrimagnetic full Heusler alloys Mn₂V Z (Z = Al, Ge)

Abstract

We report the parameter-free, density functional theory calculations of interatomic exchange interactions and Curie temperatures of half-metallic ferrimagnetic full Heusler alloys Mn2V Z (Z = Al, Ge). To calculate the interatomic exchange interactions we employ the frozen-magnon approach. The Curie temperatures are calculated within the mean-field approximation to the classical Heisenberg Hamiltonian by solving a matrix equation for a multi-sublattice system. Our calculations show that, although a large magnetic moment is carried by Mn atoms, competing ferromagnetic (inter-sublattice) and antiferromagnetic (intra-sublattice) Mn–Mn interactions in Mn2V Al almost cancel each other in the mean-field experienced by the Mn atoms. In Mn2V Ge the leading Mn–Mn exchange interaction is antiferromagnetic. In both compounds the ferromagnetism of the Mn subsystem is favoured by strong antiferromagnetic Mn–V interactions. The obtained value of the Curie temperature of Mn2V Al is in good agreement with experiment. For Mn2V Ge there is no experimental information available and our calculation is a prediction.