Sign reversal of the orbital moment via ligand states

Abstract

It is demonstrated that the coupling between spin and orbital moments in magnetic systems may---for certain materials---be reversed from antiparallel to parallel, via the influence of ligand states. This is exemplified by first-principles calculations for an intermetallic compound ${\mathrm{VAu}}_{4},$ but the effect may be found also in other classes of materials. From a computational analysis of the influence of the ligand states, and from an expression based on perturbation theory, we show that ligand states, that traditionally are known only to quench the orbital moment, may produce anomalous orbital moments that violate Hunds third rule.