Anomalous behavior of linear and nonlinear longitudinal susceptibilities below T c in a weakly anisotropic CdCr2Se4 ferromagnet

Frequency dependences of the linear and nonlinear longitudinal dynamic susceptibilities of an almost isotropic cubic CdCr₂Se₄ ferromagnet were studied experimentally in the ordered phase. It was found that at frequencies above the two-magnon creation threshold the linear susceptibility decreases as χ₁∝ω^?0.28 with increasing frequency and the nonlinear susceptibility decreases as χ_n∝ω^?0.73, irrespective of n, where n is an odd number. The observed susceptibility anomalies are due to the dipolar forces that violate the conservation of total spin.