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Nd-Co amorphous magnetic films with perpendicular magnetic anisotropy have been grown on nanostructured templates prepared with self-organized di-block poly(styrene)-block-poly(4-vinylpyridine) copolymer layers with a periodic structure of 60 nm spaced pores. These templates modify both the magnetic film topography and mechanical strain on a local scale. The effect of these structural changes is particularly noticeable in the low thickness range of the magnetic films where the transition from in-plane to out-of plane magnetization takes place. The Nd-Co films grown on the copolymer template present lower perpendicular magnetic anisotropy and, also, stronger stripe domain pinning effects in comparison with reference films grown on flat Si substrates. [ABSTRACT FROM AUTHOR]

The magnetization reversal process has been studied in amorphous magnetic films patterned with ordered arrays of antidots in the diluted limit (i.e., with small enough antidot density so that the original film anisotropy is maintained and the flux closure structures around each dot are independent from each other). The role of the material parameters in the final behavior has been analyzed comparing the results on films made of two different Co-based amorphous alloys, CoxSi1-x and CoyZr1-y, that present a similar intrinsic uniaxial anisotropy but have a different saturation magnetization. The patterned holes are found to act as weak pinning centers for the motion of the Néel walls involved in the reversal process which results in an enhancement of coercivity in certain angular ranges. However, they are only effective in the material with the lower saturation magnetization (CoxSi1-x) which can be related with the different relative sizes of the patterned holes and the Néel walls in each case. [ABSTRACT FROM AUTHOR]

Hexagonal antidot arrays have been patterned on weak perpendicular magnetic anisotropy NdCo films by e-beam lithography and lift off. Domain structure has been characterized by Magnetic Force Microscopy at remanence. On a local length scale, of the order of stripe pattern period, domain configuration is controlled by edge effects within the stripe pattern: stripe domains meet the hole boundary at either perpendicular or parallel orientation. On a longer length scale, in-plane magnetostatic effects dominate the system: clear superdomains are observed in the patterned film with average in-plane magnetization along the easy directions of the antidot array, correlated over several antidot array cells. [ABSTRACT FROM AUTHOR]

Abstract: In the present work, we introduce our latest achievements in the development of novel highly ordered composite magnetic nanostructures employing anodized nanoporous membranes as precursor templates where long-range hexagonal symmetry is induced by self-assembling during anodization process. Subsequent processing as electroplating, sputtering or pressing are employed to prepare arrays of metallic, semiconductor or polymeric nanowires embedded in oxide or metallic membranes. Particular attention is paid to recent results on controlling the magnetic anisotropy in arrays of metallic nanowires, particularly Co, and nanohole arrays in Ni membranes. [Copyright &y& Elsevier]

The transition from amorphous to polycrystalline microstructure has been studied in sputtered CoxSi1-x alloy films by structural, magneto-optical and Nuclear Magnetic Resonance measurements. For, Si is diluted into Co without significantly altering the polycrystalline microstructure, composed of a mixture of hcp and fcc grains. However, the fraction of Co atoms that contribute to the Nuclear Magnetic Resonance signal is found to decrease steeply (down to about 60atx= 0.76) suggesting a microscopic segregation of a Si rich phase that induces a large degree of disorder. This is reflected in a harder magnetic behavior and a strong anisotropy dispersion. Belowx= 0.75, the transition to an amorphous microstructure results in a sudden increase in the fraction of Co atoms within a ferromagnetic phase, indicating the recovery of the microscopic homogeneity. Also a significant enhancement of the macroscopic magnetic anisotropy is found for amorphous films with compositions right below the transition. Within the amorphous phase a second regime of Si segregation appears characterized by a constant Co local environment and constant magnetic properties. Finally, forx= 0.65 there is a significant Si enrichment in the Co environment and the films become non magnetic for compositions below this point. [ABSTRACT FROM AUTHOR]

Ni nanohole arrays are prepared by a replication process involving sputtering, polymer molding pressing, and electroplating techniques, using anodic alumina membranes as templates. Nanohole diameter to interhole distance ratio is engineered by suitable template processing. From the analysis of the magnetization curves for increasing nanohole diameter, it is concluded that coercivity increases due to the pinning of domain walls to nanoholes, while in-plane anisotropy decreases owing to local shape anisotropy effects. [ABSTRACT FROM AUTHOR]

A replica/antireplica method is here proposed for the fabrication of metallic membranes reproducing the ordering of precursor nanoporous alumina membranes. Densely packed arrays of Ni nanoholes with long range ordering of hexagonal symmetry have been prepared. The study includes the magnetic properties of Ni nanohole arrays and those for a continuous Ni film. The magnetization process has been studied by analysis of in-plane and perpendicular hysteresis loops. In addition, combined magnetic force microscopy and atomic force microscopy have allowed us to observe triangular-shaped magnetic domains related to that hexagonal symmetry. An effective in-plane magnetic anisotropy is deduced that determines an in-plane magnetization process by wall displacement which is hindered by the nanoholes in the case of noncontinuous films. [ABSTRACT FROM AUTHOR]

Stripe domains are studied in perpendicular magnetic anisotropy films nanostructured with a periodic thickness modulation that induces the lateral modulation of both stripe periods and in-plane magnetiza-tion. The resulting system is the 2D equivalent of a strained superlattice with properties controlled by interfacial misfit strain within the magnetic stripe structure and shape anisotropy. This allows us to observe, experimentally for the first time, the continuous structural transformation of a grain boundary in this 2D magnetic crystal in the whole angular range. The magnetization reversal process can be tailored through the effect of misfit strain due to the coupling between disclinations in the magnetic stripe pattern and domain walls in the in-plane magnetization configuration. [ABSTRACT FROM AUTHOR]

The motion of a domain wall in a two-dimensional medium is studied by taking into account the internal elastic degrees of freedom of the wall and geometrical pinning produced by both holes and sample boundaries. This study is used to analyze the geometrical conditions needed for optimizing crossed-ratchet effects in periodic rectangular arrays of asymmetric holes, recently observed experimentally in patterned ferromagnetic films. Exact calculation as a function of the geometry of the sample and numerical simulations have been used to obtain the anisotropic critical fields for depinning flat and kinked walls in rectangular arrays of triangles. The aim is to show with a generic elastic model for interfaces how to build a rectifier able to display crossed-ratchet effects or effective potential landscapes for controlling the motion of interfaces or invasion fronts. [ABSTRACT FROM AUTHOR]