On the origin of `giant moments' in dilute alloys

Abstract

The occurrence of giant magnetic moments (similar 12 to 14 Bohr magnetons) in some dilute alloys of Fe or Co dissolved in Pd, Pt or mixed 4d-5d series systems is theoretically analysed by taking into account the exchange interaction between the impurity and the spins of neighbouring host atoms, lying within a radius of the order of 8 A, embracing over 100 atoms. The model Hamiltonian considered includes, in addition to the usual s-d mixing, the mixing between the host localized states (unfilled inner shells) and conduction s-electron states, as well as the exchange interaction mentioned above. Making use of the double-time Green function technique, the net moment associated with the impurity centre and the host neighbours is obtained and found to be a monotonically increasing single-valued function of the matrix susceptibility χ. The matrix susceptibility is attributed to the incompletely filled inner shells (as amply evidenced by the observed paramagnetic temperature dependence of χ for Pt, Pd). A plot of the theoretical curve for the net moment against the host susceptibility is given and is in good agreement with available experimental data.