Tuning the orbital moment in transition metal compounds using ligand states

The influence of ligand states on the orbital magnetism of a 3d atom in a ferromagnetic compound has been studied using an ab initio technique. It is shown, using VAu₄, MnAu₄ and VPt₃ as examples, that the large spin-orbit coupling of the 5d atom is responsible for the reversal of the coupling between the V(Mn) spin and orbital moments with respect to that for similar compounds. The VAu₄ compound has a large magneto-crystalline anisotropy (MCA) and the spin-up states are completely occupied, which makes its MCA proportional to the orbital moment anisotropy as stated by Bruno's perturbative formula (Bruno P 1989 Phys. Rev. B 39 865). For the latter compound it is also shown that a partial substitution of copper for gold decreases the vanadium orbital moment and hence the MCA. The ligand state effects on the orbital moment together with this alloying procedure may initiate a new approach in the search for ultra-soft magnetic materials.