Spin waves in multiple-spin-density-wave systems

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Abstract
The spin wave modes in an anisotropic Heisenberg model are investigated for a triple-spin-density-wave (TSDW) ground state in a FCC lattice. Explicit solutions are obtained in the diagonal-exchange regime in all directions. The solutions are also given in the (0,0, xi ) and ( xi , xi ,0) directions for the above model including non-diagonal exchange and a crystal-field term. Besides the usual acoustic spin wave modes the authors find a spin wave mode with a dispersion similar to that of a ferromagnetic spin wave. This latter mode couples weakly to neutrons. They obtain qualitatively different results to Jensen and Bak (1981) who appear to drop the off-diagonal-exchange terms. They also compare the results between a TSDW and those due to a distribution of single spin-density waves (SSDW) polarised along each of the axis directions and discuss their effect on width measurements.