Spin waves and temperature dependence of magnetization in strained EuS films

Abstract

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.

Interlayer Exchange Coupling in Semiconductor EuS-PbS Ferromagnetic Wedge Multilayers

“…Qualitatively, the magnetization loops of EuS-PbS wedge superlattices are similar to the case of previously studied antiferromagnetically coupled EuS-PbS superlattices and trilayers grown on KCl (001) substrates [2][3][4][5][6]. However, a characteristic low field linear "plateau" with a well defined external magnetic switching field observed in trilayer structures was not clearly observed in the wedge structures and could only be determined for the EuS-PbS structure with the thinnest PbS spacer of 0.3 nm.…”

“…Ferromagnetic transition temperature in bulk EuS crystals equals 16.5 K whereas in EuS epitaxial layers grown on KCl substrates the Curie temperature increases to 17.5 K due to thermal strain brought about by the difference of thermal expansion coefficients of the layer and the substrate [1,2]. In EuS layers thinner than about 3 nm the size effect in magnetic properties is also observed [2,5] with a Curie temperature reduced in ultrathin (0.6 nm) layers down to about 2/3 of its value in 0.1 µm thick layers. It was found experimentally that in EuS-PbS semiconductor multilayers with ultrathin (about 1 nm) PbS layer, the ferromagnetic layers of EuS are coupled antiferromagnetically via the nonmagnetic PbS spacer.…”

Physical properties of quantum‐confined europium sulfide nanocrystals

“…The magnetic properties attributed to Eu 2+ ions are explained by the competition between the ferromagnetic (FM) indirect exchange among nearest neighbour (J 1 ) and the antiferromagnetic (AF) superexchange among next-nearest neighbour (J 2 ) europium ions. For EuS nanoparticles with small lattice constants (a 0 = 0.5968 nm at T = 300K), the FM exchange dominates [5][6][7][8][9]. When the size of a EuS nanocrystal approaches the quantum confinement regime at approximately 2.0 nm, it contains less than 250 atoms.…”

Influence of substrates on the dynamical properties of ferromagnetic semiconducting thin films

“…EuS thin films were theoretically studied by Mueller and Nolting [18] and by Swirkowicz and Story [19] but the influence of substrates is not investigated. In [18] is presented the temperature-and layerdependent electronic structure of a thin EuS(100) film using a combination of first-principles and model calculations, the latter based on the ferromagnetic Kondo lattice.…”

“…Special attention is devoted to the appearance of magnetic 5d-surface states. Magnetic properties of ultrathin EuS films with strain effects taken into account are studied within the framework of the Green function formalism [19]. Strong influence of stress on spin-wave dispersion relations, especially on high-energy modes, is found.…”