Rotational pseudospin-phonon interactions at finite frequencies

A procedure is described for treating pseudospin-phonon interactions with a rotationally invariant formalism valid for all frequencies less than resonant frequencies 0. The results of thermodynamic calculations valid at zero frequency are combined with those of a mode-mode calculation for the coupling to the m = 0 spin mode. The results which are properly rotationally invariant and valid for all, where -1 is the relaxation rate of the m = 0 mode, are restricted to the limit 0. © 1976 The American Physical Society.