Theory of Spin Waves in Nonferromagnetic Metals

Abstract

A simple quantum-mechanical theory of spin waves in nonferromagnetic metals has been developed. This theory consists of a description of the spin-wave excitations superimposed on the paramagnetic Hartree-Fock ground state of an interacting electron gas subjected to a constant uniform magnetic field. Use has been made of a gauge-independent density-matrix formalism. It is shown that to first order in the magnetic field the transport equation for the transverse spin magnetization has the same form as the corresponding phenomenological Fermi-liquid equation proposed by Silin and by Platzman and Wolff. It is also shown that for large fields, such that the cyclotron radius is smaller than the interelectronic distance, the term in the transport equation related to the cyclotron motion of the electrons is not affected by the exchange interactions. The theory presented here lends additional credence to the validity of Platzman and Wolff's phenomenological analysis of the experimental spin-wave spectra in the alkali metals.