Strain in single-crystalRFe2(110)thin films(R=Y,Sm, Gd, Tb,Dy0.7Tb0.3,Dy, Er, Lu)

Abstract

Single-crystalline $R{\mathrm{Fe}}_{2}(110)$ compounds $(R=\mathrm{Y},$ Sm, Gd, Tb, ${\mathrm{Dy}}_{0.7}{\mathrm{Tb}}_{0.3},$ Dy, Er, and Lu) have been grown by molecular-beam epitaxy. Compared to the bulk compounds, the thin films exhibit modifications of the magnetic anisotropy, related to the strains induced during deposition. We present here a detailed determination of in-plane and out-of-plane parameters using x-ray and neutron diffraction. $R{\mathrm{Fe}}_{2}$ films and $R{\mathrm{Fe}}_{2}{/\mathrm{Y}\mathrm{F}\mathrm{e}}_{2}$ bilayers have been deposited on a Nb buffer covered with Fe. Both systems are strained compared to bulk compounds: they are expanded in the plane of epitaxy and compressed along the growth direction. For single $R{\mathrm{Fe}}_{2}$ films, the strains do not depend on the lattice parameters of the corresponding bulk compounds, i.e., on the large mismatch between the film and the buffer (around 10%). The sign and the values of the strains are explained with a model of differential thermal contraction between the film and the substrate. For $R{\mathrm{Fe}}_{2}$ films involved in $R{\mathrm{Fe}}_{2}{/\mathrm{Y}\mathrm{F}\mathrm{e}}_{2}$ bilayers, the mismatch between $R{\mathrm{Fe}}_{2}$ and the ${\mathrm{YFe}}_{2}$ layer is smaller and the strains in the $R{\mathrm{Fe}}_{2}$ films do depend on the bulk lattice parameters. Their evolution can be explained with an elastic model.