Spin waves in ferromagnetic metals

Abstract

A qualitative discussion is given of the low-lying states of a ferromagnetic metal and the consequent low -temperature thermodynamic properties of the system. It is concluded that a typical low-lying state differs from the ground state by a number of independent particle excitations, such as are considered in Stoner’s collective electron theory, and a number of exciton-like excitations, in which an electron of minority spin is bound to a hole of majority spin, which correspond to spin waves. The low temperature specific heat and the deviation of the magnetization from saturation may then both be expressed as the sum of two terms, one typical of collective electron theory and one of spin wave theory. A formal proof is given of the existence of spin waves of long wavelength in metals and a general method of calculating their energies is outlined. Herring’s results on spin-wave energies are obtained as a special case.