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Ho films of thickness varying from 100 Å up to 4000 Å and [Ho(x Å) - Zr(y Å)]n multilayers with 7 x , y 30 were grown by evaporation under ultravacuum conditions on an oxidized Si(100) substrate covered with a Zr buffer layer. The x-ray diffraction patterns recorded for the transferred momentum either along the -axis or in the basal plane of the hexagonal close-packed structure show that holmium suffers a permanent in-plane compression in films thinner than 200 Å and Ho(x Å ) - Zr(30 Å) multilayers with x 30. Low-temperature magnetization measurements indicate that the magnetic behaviour of Ho is strongly modified by epitaxial strains. The data are consistent with an enhancement of in-plane ferromagnetic order inside the Ho blocks in the Ho-Zr multilayers. A periodic dependence of the squareness of the hysteresis loop on the thickness of the Zr layers is observed in Ho(30 Å) - Zr(x Å) multilayers, which gives evidence for the existence of interlayer magnetic coupling. The out-of-plane magnetic anisotropy generated by Ho - Zr interfaces in a series of Ho(x Å) - Zr(30 Å) multilayers is found to be strong enough to compensate the in-plane anisotropy as the thickness of the Ho layers is decreased to about three monolayers. The variation of the anisotropy against the Ho layer thickness is satisfactorily reproduced with a rough crystal-field model using the point-charge approximation.

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