Magnetisation distribution in a partially disordered Au4V alloy

The magnetization density distribution in a partially ordered single crystal of Au4V has been determined using polarized neutron diffraction. The results show that the magnetization is essentially localized on the vanadium sites of the ordered structure. If it is assumed that only the vanadium atoms on these sites carry a moment then the localized moment per vanadium atom is 0.58 +- 01 mu B. The magnetic form factor of this localized moment has been shown to be in good accord with that calculated by Freeman and Watson [Acta Cryst. 14:231(1961)] for the vanadium 3d34s2 configuration. The magnetization density distribution obtained by Fourier inversion shows some aspherical characteristics. A quantitative measure of the asphericity was obtained from a least squares fit between the measured magnetic structure factors and a model in which a localized vanadium atom carrying a moment is superposed on a uniform magnetization density. The localized moment was allowed to have both spin and orbital contributions within the dipole approximation. The spin moment was allowed to assume an aspherical distribution consistent with its four-fold symmetry. The parameters of the model obtained from the refinement suggest that there is a small negative orbital moment of -0.02 mu B, a negative background polarization of -2 x 10-4 mu B A-3 and indicate that the spin density is extended in the directions of the nearest neighbor vanadium sites