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 f erromagnetic compound has been studied using an ab initio technique. It is shown, using VAu4, MnAu4 and VPt3 as examples, that the large spin-orbit co upling of the 5d atom is responsible for the reversal of the coupling betwe en the V(Mn) spin and orbital moments with respect to that for similar comp ounds. The VAu4 compound has a large magneto-crystalline anisotropy (MCA) a nd the spin-up states are completely occupied, which makes its MCA proporti onal to the orbital moment anisotropy as stated by Bruno's perturbative for mula (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 vanadiu m orbital moment and hence the MCA. The ligand state effects on the orbital moment together with this alloying procedure may initiate a new approach i n the search for ultra-soft magnetic materials.