Spin waves and temperature dependence of magnetization in strained EuS films

Magnetic properties of ultrathin EuS films with strain effects taken into account are studied within the framework of the Green function formalism. Standard RPA and more general procedures employed by Callen are used for decoupling of higher order functions generated by exchange and anisotropy terms, respectively. Parameters of the model such as exchange integrals in strained structures and anisotropy constants are estimated on the basis of experimental data obtained with use of SQUID and FMR techniques. Strong influence of stress on spin-wave dispersion relations, especially on high-energy modes, is found. A shift of curves representing magnon DOS towards higher energies is obtained in the presence of stress. All these modifications lead to a slower decrease of the magnetization with increasing temperature and to an enhancement of the critical temperature. The results are consistent with experimental data. Investigations of the course of the magnetization curves for various film thickness also confirm experimental results.