Atomic Moments in Alloys

Abstract

The saturation moment of ferromagnetic alloys has been considered from the point of view of the collective electron theory. Perturbations in band shape due to the fluctuating lattice potential are considered and are found to be more important in some cases than the simple effects of changing electron density characteristic of the usual treatment of alloys. The influence of order on the moment is treated on the basis of Slater's theory of the relation between the long range order and the energy bands in an alloy. Results of measurements of electronic specific heat and Hall effect are presented which make possible a model capable of explaining the unique effects of the order-disorder transformation in ${\mathrm{Ni}}_3$Mn on this basis. In other alloys, particularly those which do not follow the Slater-Pauling curve or the classical band model, the saturation properties are attributed to the perturbations in the band resulting from the presence in the lattice of ions with different potentials as seen by the itinerant electrons. The screening of the positive Coulombic charge on these ions is accomplished by fluctuations in local electron density of the Fermi gas in some cases and by localized bound states in other cases. The effect on the magnetic properties in these two alternative cases can be explained and correlated with changes in electrical resistivity on alloying. Atomic moments of the constituent atoms for some ordered alloys have been calculated and are in good agreement with the experimental values found by Shull in neutron diffraction experiments.