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

Abstract

We report the parameter-free, density functional theory calculations of interatomic exchangeinteractions and Curie temperatures of half-metallic ferrimagnetic full Heusler alloysMn2V Z (Z = Al,Ge). To calculate the interatomic exchange interactions we employ the frozen-magnonapproach. The Curie temperatures are calculated within the mean-fieldapproximation to the classical Heisenberg Hamiltonian by solving a matrixequation for a multi-sublattice system. Our calculations show that, although alarge magnetic moment is carried by Mn atoms, competing ferromagnetic(inter-sublattice) and antiferromagnetic (intra-sublattice) Mn–Mn interactions inMn2V Al almost cancel each other in the mean-field experienced by the Mn atoms. InMn2V Ge the leading Mn–Mn exchange interaction is antiferromagnetic. In bothcompounds the ferromagnetism of the Mn subsystem is favoured by strongantiferromagnetic Mn–V interactions. The obtained value of the Curie temperature ofMn2V Al is in good agreementwith experiment. For Mn2V Ge there is no experimental information available and our calculation is a prediction.