Order-parameter–conserving anitferromagnets

In a fcc lattice it is possible to have conserved staggered magnetization if the spin coupling constants are very anisotropic and fulfill certain conditions, which are almost realized in CeAs. The result is a spin-wave spectrum that is quadratic in q with a very small gap. Other consequences are the degeneracy of single and triple q antiferromagnetic states, sensitivity to random strains and diffusive modes above ${\mathrm{T}}_{\mathrm{N}}$. .AE