Dynamic Spin Hamiltonian Formalism and Mössbauer Study of Spin—Lattice Relaxation of Paramagnetic Fe3+ (6S) Ions

Abstract

AbstractIn a crystal field potential the 6S state of a paramagnetic 57Fe3+ (3d5, 6S) ion splits into three Kramers spin doublets Sz = ± 5/2, ± 3/2, and ± ½ and each doublet produces its own Mössbauer magnetic hyperfine spectrum at low temperatures as a result of the slow spin relaxation rate. These Mössbauer hyperfine spectra are used to study the temperature dependence of Fe3+ spin lattice relaxation rate falling in the region 106 to 109 s−1. The dynamic spin Hamiltonian formalism is utilised to explicitly calculate the spin—lattice relaxation rate of the three Kramers doublets for one‐phonon and two‐phonon processes in different temperature regions. It is further assumed that the various modes of acoustic phonon propagation are direction independent, the phonon spectrum is of Debye type, and the dynamic crystal field parameters are very similar to the static ones. It is found that for Fe3+ ions the one‐phonon relaxation process is most dominant and the theoretical results are in a very good agreement with the experimental observations. These calculations may be equally applicable to other S‐state paramagnetic ions.