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

The temperature dependence of the hyperfine parameters of the Fe-57 nuclei in yttrium iron garnet Y3Fe5O12 (YIG) between room temperature and the Curi e point was studied by means of conventional Mossbauer transmission spectro scopy. The critical exponent beta, which describes the temperature dependen ce 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 temperatur e region just below the Curie point relaxation of the internal hyperfine fi elds could be observed. The phase transition at the Curie point shows a dis tinct dependence on the grain size in the sample.