Spin waves and temperature dependence of magnetization in strained EuS films

Magnetic properties of ultrathin EuS films with strain effects taken into a ccount are studied within the framework of the Green function formalism. St andard RPA and more general procedures employed by Callen are used for deco upling of higher order functions generated by exchange and anisotropy terms , respectively. Parameters of the model such as exchange integrals in strai ned structures and anisotropy constants are estimated on the basis of exper imental data obtained with use of SQUID and FMR techniques. Strong influenc e of stress on spin-wave dispersion relations, especially on high-energy mo des, is found. A shift of curves representing magnon DOS towards higher ene rgies is obtained in the presence of stress. All these modifications lead t o a slower decrease of the magnetization with increasing temperature and to an enhancement of the critical temperature. The results are consistent wit h experimental data. Investigations of the course of the magnetization curv es for various film thickness also confirm experimental results.