Effects of off-diagonal hyperfine interaction on mossbauer relaxation spectra

The Mossbauer line shape for systems where the nucleus is under the influence of a static axial electric field gradient and a time-dependent magnetic hyperfine interaction is considered. Ferric hemin serves as an example of the systems studied. The time dependence in the hyperfine interaction arises owing to relaxation in the ionic system, caused by the dipole-dipole interaction of the ions, between the ionic levels split by a crystalline field. This spin-spin relaxation rate is temperature dependent, slowing down somewhat as the temperature is increased. Its effect on the coupled nucleus-ion system is studied in perturbation theory based on the stochastic-theory model of Clauser and Blume. The presence of off-diagonal terms in the hyperfine interaction is found to produce some new interesting effects in addition to earlier results obtained by Blume in which the hyperfine interaction was assumed to be diagonal. Comparison of theory with experiments is made