Strain-induced magnetic anisotropy in single-crystal RFe2(110) thin films (R = Dy, Er, Tb, Dy0.7Tb0.3, Sm, Y)

摘要

RFe2(110) single-crystal films have been grown by molecular-beam epitaxy (R = Y, Sm, Gd, Tb, Dy0.7Tb0.3, Dy, Er). The films are strained compared to bulk compounds and both sign and value of the strains are explained with a model of differential thermal contraction between the film and the substrate. Mossbauer spectrometry and macroscopic magnetization measurements demonstrate that the magnetic anisotropy is modified in magnetostrictive (110) films compared to corresponding bulk systems. In DyFe2(110) and ErFe2(110), the easy magnetization direction is the same as in bulk compounds at low temperature ((100) and (111), respectively). The magnetic moments rotate towards (110) directions when the temperature increases. At room temperature, they are close to the [110] in-plane direction in DyFe2(110) and close to the [110] perpendicular to the plane direction in ErFe2(110). In TbFe2(110), the magnetization easy direction is (111) whatever the temperature is. For compounds which present a thermal spin reorientation in bulk form (Dy0.7Tb0.3Fe2 and SmFe2), this rotation is limited in the thin films. As expected from a nonmagnetostrictive compound, the epitaxial strains do not induce a thermal evolution of the easy magnetization direction in YFe2 films: it remains independent of temperature, although slightly shifted from (111) due to a variation of the exchange anisotropy between iron ions induced by the strains. Theoretical diagrams of the magnetization direction have been calculated as a function of strain, between 4.2 K and room temperature. They show the influence of the strains (and more particularly their sign), and of the anisotropy and magnetoelastic constants on the easy magnetization direction. The model permits us to reproduce the experimental results. [References: 29]