Linewidth of ferromagnetic resonance for systems with anisotropic damping

Theory has predicted that the damping of magnetization dynamics may be anisotropic; i.e., it may depend on the momentary orientation e(t) of the magnetization in the crystal. In the present Brief Report it is shown that in general this anisotropy is averaged out at least to some extent for the special trajectory e(t) of the magnetization vector in a ferromagnetic-resonance (FMR) experiment. In principle it may be that there is no anisotropy of the FMR linewidth although the damping is strongly anisotropic and although this anisotropy will be essential in a more complicated trajectory e(t) of the magnetization vector.