SPIN WAVES AND OTHER MAGNETIC EXCITATIONS IN NON-FERROMAGNETIC METALS

The transverse dynamical spin susceptibility of a metal in a static magnetic field is calculated within the random phase approximation. The new feature of the work is that the existence of Landau levels is taken into account. The dynamical susceptibility is used to discuss the spin-flip excitations of the system. These include Stoner single-particle excitations, spin waves and some other collective modes. The spin-wave spectrum obtained is directly related, in the long-wavelength limit, to that obtained by Platzman and Wolff using Fermi liquid theory. The pronounced anisotropy of the spin-wave spectrum, as observed by Schultz and Dunifer in the alkali metals, is obtained in the present theory through the introduction of the Landau levels. A discussion is given of qmax, the wave vector at which the spin waves merge with the Stoner continuum. Other collective modes obtained include some in the nature of cyclotron resonances with spin-flip, and some which lead to an instability of the normal Hartree-Fock state at very low temperatures, as discussed previously by Celli and Mermin.