Anisotropy Effects in Electron Spin Resonance in Metals

The magnetization of a nonferromagnetic metal has been obtained from the solution of a Boltzmann equation, assuming that the Fermi surface is spherical but the $g$ factor and spin-lattice relaxation time are wave-vector-dependent. It is found that the effective diffusion constant appearing in the denominator of the magnetization is complex, which corresponds to a branch of spin-wave excitations. We find that this effect is too small to contribute to the spin-wave resonances observed in sodium, but a small effect in the line shape of the resonance in a thick sample is shown to occur.