Ferromagnetism in Dilute Alloys

Abstract

An interaction between conduction electrons is obtained by eliminating the exchange interaction between conduction electrons and localized spins in metals by means of a canonical transformation. This procedure of elimination is similar to that used in obtaining the electron-electron interaction due to phonons in the theory of superconductivity. The derived electron-electron interaction, however, is an exchange type and of repulsive nature, contrary to the case of electron-phonon interaction. As an illustrative application of the above result we calculate the paramagnetic susceptibility of conduction electrons. The susceptibility is increased when we include this new effective exchange interaction which adds to the enhancement caused by the Coulomb interaction. With this simple fact some of the interesting problems in dilute alloys are explained. The ferromagnetism of Pd alloys containing only 0.1 at.% of Fe, for example, is attributed to that of conduction electrons which is made possible by electron-electron interaction which acts additively with the Coulomb interaction.