Magnetic excitations in spin-density-wave systems

Abstract

We propose a versatile phenomenological model in which there is no magnetic anisotropy and yet which is suitable for a description of linearly polarized incommensurate magnetic structure (e.g., as in chromium) as well as ferromagnets, antiferromagnets, helical structures, and what we call even-commensurate and odd-commensurate (a sort of weak ferromagnet) structures. The frequencies and eigenvectors of the long-wavelength spin-wave excitations for all of these structures are obtained and compared; of particular interest is the linearly polarized incommensurate case for which well-defined long-wavelength spin-wave excitations having a linear dispersion relation are shown to exist.