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.

The magnetically glassy behavior of mechanically alloyed Fe 61 Re 30 Cr 9 is reported in detail, including a static and dynamic study of the freezing process, the observation of aging in a mechanically alloyed sample, Mössbauer analysis, and annealing experiments. Despite the clear collective character of the low-temperature change of regime, no thermodynamical spin-glass mean-field transition could be proved. On the other hand, the careful comparison of the magnetic behavior with that reported in strongly interacting fine particles systems hinted towards the presence of that kind of particles in our samples. Structural considerations based on XRD, Mössbauer, and the evolution of the ac susceptibility peaks upon annealing pointed to the existence of very fine Fe-rich clusters able to support a magnetic moment, confirming the diagnosis extracted from the magnetic dynamics analysis. The argument is strengthened by the study of the effects of milling on the freezing temperature in a second sample showing a similar behavior: Fe 35 Al 50 B 15 . The explanation can be extended naturally to previously reported mechanically alloyed, spin-glass-like samples, which hints towards the generalization of our interpretation.

The interdiffusion process between Gd and Co has been investigated in several series of multilayered films consisting of Co and different GdCo alloys (Gd1−xCox)/Co (x=0, 0.37, and 0.60). Grazing incidence x-ray profiles provided a preliminary insight into the structure of the samples. Electrical resistivity measurements were performed in a temperature range between 8 and 300 K. For the three series, the room temperature electrical resistivity shows a clear fall once a critical Co thickness is surpassed, which we interpret as due to the growth of pure polycrystalline Co between the alloy layers. A simple model allows us to quantify the amount of Co diffused into the alloy layer. The results will be discussed considering the possible decrease of interdiffusion effects when Co is deposited onto the more stable GdCo alloys. This leads to a well defined multilayered structure, something that is essential for practical applications and for the theoretical study of its underlying physics.

The interdiffusion process in Gd1-xCox/Co multilayered systems has been investigated, in several series of samples made by sputtering, with different values of the Co content in the alloy (x). Grazing-incidence x-ray profiles and the electrical resistivity, together with magnetic measurements at room temperature, allow us to monitor and quantify the interdiffusion between layers as well as their magnetic properties. It is shown that this interdiffusion occurs on increasing the Co content of the alloy layer up to around 60% Co. In the x = 0.60 series the interdiffusion was found to be negligible and therefore a very good structure was obtained, while the ferrimagnetic structure between layers is preserved. The improved multilayered structure obtained in this system could lead to the development of new technological applications.

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