We present a structural and magnetic study of La0.7Ca0.3MnO3 epitaxial films (the thickness ranges from 2.4 to 80 nm) on SrTiO3. Their structure, as obtained by x-ray diffraction, is orthorhombic with a 45° rotated 2×2 square lattice, referred to the SrTiO3 substrate, in the film plane. The 2.4 nm film adopts a different structure as evidenced by the extinction of particular diffraction peaks and supported by the behavior of the size of the in-plane structural domains. While no important structural changes are detected for the other films as the layer thickness is reduced, Tc decreases drastically while the remanent magnetization is constant. Tc follows the functional dependence of a mean field approximation for the limitation of the divergence of the spin–spin correlations by the film thickness.

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Ion beam patterning of a nanoscale ripple surface has emerged as a versatile method of imprinting uniaxial magnetic anisotropy (UMA) on a desired in-plane direction in magnetic films. In the case of ripple patterned thick films, dipolar interactions around the top and/or bottom interfaces are generally assumed to drive this effect following Schlömann's calculations for demagnetizing fields of an ideally sinusoidal surface [E. Schlömann, J. Appl. Phys. 41, 1617 (1970)]. We have explored the validity of his predictions and the limits of ion beam sputtering to induce UMA in a ferromagnetic system where other relevant sources of magnetic anisotropy are neglected: ripple films not displaying any evidence of volume uniaxial anisotropy and where magnetocrystalline contributions average out in a fine grain polycrystal structure. To this purpose, the surface of 100 nm cobalt films grown on flat substrates has been irradiated at fixed ion energy, fixed ion fluency but different ion densities to make the ripple pattern at the top surface with wavelength Λ and selected, large amplitudes (ω) up to 20 nm so that stray dipolar fields are enhanced, while the residual film thickness t = 35–50 nm is sufficiently large to preserve the continuous morphology in most cases. The film-substrate interface has been studied with X-ray photoemission spectroscopy depth profiles and is found that there is a graded silicon-rich cobalt silicide, presumably formed during the film growth. This graded interface is of uncertain small thickness but the range of compositions clearly makes it a magnetically dead layer. On the other hand, the ripple surface rules both the magnetic coercivity and the uniaxial anisotropy as these are found to correlate with the pattern dimensions. Remarkably, the saturation fields in the hard axis of uniaxial continuous films are measured up to values as high as 0.80 kG and obey a linear dependence on the parameter ω2/Λ/t in quantitative agreement with Schlömann's prediction for a surface anisotropy entirely ruled by dipolar interaction. The limits of UMA tuning by a ripple pattern are discussed in terms of the surface local angle with respect to the mean surface and of the onset of ripple detachment.

We have performed composition depth profiles and other structural experiments on Gd/Co multilayers and bilayers. Analysis of Auger depth profiles indicates a strongly asymmetric diffusion, especially of Co into the Gd layers. In multilayers, it is found that Co diffuses throughout the Gd layers and forms a Gd1−xCox amorphous alloy (x=0.29–0.35) that is limited at nearly the eutectic composition (x=0.37). Therefore, if the Co layers are nominally not too thin (≳3 nm), the multilayer mainly comprises an amorphous layers of composition around Gd0.7Co0.3 and layers of pure Co. Thin Co layers (3–7 nm) present broad halos in x-ray diffraction scans at wave vectors characteristics of pure cobalt. Thick layers (≳10 nm) show crystalline peaks with a coherence size (ξ⊥) shorter than its own layer thickness, suggesting the existence of amorphous phases next to the interface. This can be explained by the growth of pure and amorphous Co up to a thickness of 2–4 nm on the amorphous Gd alloy seed, but further Co deposition consists of hcp crystalline grains.