Magnetic Properties of Dilute Magnetic Alloys and of the Rare Earth Metals

Dilute alloys of paramagnetic atoms in Cu or the noble metals have been found to exhibit ferromagnetism as well as antiferromagnetism. This is of particular interest because the origin of the magnetic behavior cannot lie in the customary Heisenberg exchange interaction between nearest neighbors because of the large separation between the paramagnetic atoms in dilute alloys. A similar situation exists in the rare earths where nearest neighbor 4f−4f direct exchange is negligible. The spin coupling can be explained by taking account of the direct exchange interaction between the paramagnetic atoms and the conduction electrons and by superexchange. To describe the superexchange coupling it is necessary to know the energy levels of the paramagnetic atom in the solid. The results of a Hartree-Fock analysis of this problem are briefly discussed. A generalization of a previous molecular field treatment is also given.