Character of Excitations in Substitutionally Disordered Antiferromagnets

Magnetic excitations in several single crystals of the systems K(Co,Mn)${\mathrm{F}}_3$ and (Co, Mn)${\mathrm{F}}_2$ have been studied by neutron inelastic scattering. It is found that two branches of well-defined magnetic excitatios, both of which exhibit propagating character, occur at certain compositions. The dispersion relation for two branches of propagating excitations cannot be adequately described by current theories, but an extension of Anderson's criterion for localization in disordered alloys gives approximate agreement with the observed character.