Mossbauer investigation of spin-lattice relaxation of paramagnetic Fe3+ ions in NH4Al(SO4)2.12H2O

Mossbauer spectra of Fe3+ in NH4Al(SO4)2.12H2O have been obtained in the temperature range of 79-295K with applied magnetic fields of 5.7-12.3 kG. The spectra exhibit electronic spin relaxation with a relaxation time that depends strongly on the temperature and to some extent on the applied field. The spectra have been successfully fitted using the stochastic relaxation model. The relaxation is explained in terms of two spin-lattice relaxation processes: first-order Raman processes involving an internal vibrational mode of the Fe(H2O)6 3+ complex and a contribution which has been attributed to spin-lattice relaxation processes induced by critical crystal-field fluctuations, associated with the phase transition in the alum.