Dependence of magnetism ofVAu4alloy on the state of chemical order: A first principles study

Abstract

The strong dependence of the magnetic properties of the alloy $\mathrm{V}{\mathrm{Au}}_{4}$ upon the degree of chemical order has been a subject of intense experimental studies and controversial theoretical interpretations. In the framework of density functional theory using the coherent potential approximation embodied in the Korringa-Kohn-Rostoker method, we perform first principles calculations of $\mathrm{V}{\mathrm{Au}}_{4}$ varying the degree of atomic chemical order from a disordered fcc alloy to the fully ordered $\mathrm{Mo}{\mathrm{Ni}}_{4}$-type structure. In contrast to the conventional point of view, partially also based on earlier first principles studies of the ordered structure, our results suggest a localized character of the vanadium moments rather than being weakly itinerant. Moreover, we find that in the fully ordered alloy an antiferromagnetic state is more stable than the ferromagnetic. This finding leads to a significant revision of the earlier descriptions of magnetism in $\mathrm{V}{\mathrm{Au}}_{4}$, which were based either on itinerant or local moment pictures. Investigating fcc Au-V alloys richer in vanadium, we also study the role of local environment effects on the stabilization of the magnetic moments at the V atoms and advocate a ferrimagnetic character of the experimentally observed state with a small spontaneous magnetization.