Phase transitions in thin magnetic layers

Some of the properties of thin magnetic layers, concerning the ferromagnet-antiferromagnet transitions, are described. The isotopic Heisenberg Hamiltonian has been discussed and the conclusion has been drawn, that the anisotropic interaction term has to be introduced into the Hamiltonian in order to describe the experimental result of the existence of the spontaneous magnetization in thin magnetic layers. The possibility to calculate the spontaneous magnetization in thin magnetic layers by the use of the molecular field approximation and the spin waves method has also been discussed. The theory of the critical neutron scattering on bulk materials has been adapted to the case of a thin target and possibilities given by the observation of the critical neutron scattering on thin targets are discussed. (S.B.)