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We have determined the rhombohedral magnetoelastic stress of a Laves phase TbFe2 (110) single-crystal film, grown by molecular-beam epitaxy. The film thickness was 1300 Å. The magnetoelastic stress was directly measured by using a low-temperature cantilever capacitive method, between 300 and 10 K. The isotherms clearly display the coercive field but, unlike bulk alloy behavior, do not saturate even at the maximum field of 12 T. The determined rhombohedral magnetoelastic parameter of the film is Bε,2=−0.43 GPa, at 0 K and 12 T, which is 0.67 times the value for bulk TbFe2. Bε,2 follows a power m3 of the reduced magnetization m, indicating a single-ion volume origin for the rhombohedral magnetoelastic stress of this film. Measurements performed in a 300 Å TbFe2 (110) film deposited onto a YFe2 buffer show that the coercive field is drastically lowered and that the magnetoelastic distortion is negligible.

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Thin films of DyFe2 and ErFe2 have been epitaxially grown along the [110] direction. At 4.2 K, the easy magnetization axis in the films, determined by Mössbauer spectroscopy, is the same as in bulk compounds (i.e. 100 for DyFe2 and 111 for ErFe2). At 300 K, the magnetic moments, which remain in the same direction as at 4.2 K in bulk compounds, rotate towards 110 directions in thin films: they are close to the in-plane [110] direction in DyFe2 films, and close to the perpendicular-to-the-plane [110] direction in ErFe2 films. These modifications of the magnetic anisotropy are related to the epitaxial strains, and to the sign and the relative importance of the anisotropy and magnetoelastic constants of the compound.