The temperature dependence of the hyperfine parameters of YIG below the Curie point

The temperature dependence of the hyperfine parameters of the 57Fe nuclei in yttrium iron garnet Y3Fe5O12 (YIG) between room temperature and the Curie point was studied by means of conventional Moessbauer transmission spectroscopy. The critical exponent β, which describes the temperature dependence of the magnetic hyperfine field of 57Fe in YIG, was found to be 0.29(1) and 0.33(1) in the [a]- and (d)-sublattice, respectively. In the temperature region just below the Curie point relaxation of the internal hyperfine fields could be observed. The phase transition at the Curie point shows a distinct dependence on the grain size in the sample