Ferromagnetic resonance in K2CuF4: magnetostatic modes, electromagnetic propagation effects and dependence of the anisotropy field on temperature and external magnetic field

Abstract

Ferromagnetic resonance of quasi-two-dimensional K2CuF4 Has been studied for various frequencies between 10 and 100 GHz (external magnetic fields between 0.5 and 3.5T) at various temperatures up to 30K. For 10 and 35 GHz, the measurements were performed with conventional microwave techniques and the spectra exhibited structures which are analysed as originating from magnetostatic modes. For higher frequencies, a quasi-optical method has been used and here the structures in the absorption are explained as propagation effects and ferromagnetic polaritons. From the ferromagnetic resonance data, the authors obtain the temperature and field dependence of the anisotropy field HA and of the saturation magnetisation M0 or of the combination A=HA+M0, respectively. The temperature dependence of the latter follows a A(T)=A(0)(1-CT32/) law with decreasing values of C for increasing external field, i.e. increasing resonance frequency. The temperature dependence of the magnetisation and the anisotropy field alone has been derived mainly on the basis of theoretical considerations.