Change in the critical exponent of magnetization in maghemite in the temperature range of the structural phase transition

The magnetization of maghemite and magnetite thin films is measured as a function of the temperature and orientation of the film. It is established that the temperature dependence of the spontaneous magnetization deviates from the Bloch law at low temperatures and is adequately described by the linear function M/M _s = 2.2(1-T/T _C) below the Curie temperature T _C. The linear temperature dependence of the magnetization below the Curie temperature is explained by the change in the spin of iron ions in tetrahedral positions due to local deformations of the crystal lattice.