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X ray resonant magnetic scattering (XRMS) was used to characterize the magnetization of 2D arrays of trilayer submicron magnets. The interpretation of the data required the understanding of the morphology of the magnets which was also deduced from the scattered intensity. The magnets consisted of two magnetostatically coupled ferromagnetic layers separated by a non-magnetic spacer. The scattered intensity from the disks resulted to be dependent on the disks surface curvature. This made the collected intensity at each Bragg reflection (BR) to be correlated to the reflected light from locations of the disk with the same angle of curvature. Due to this, quantitative information was obtained, averaged over the disks illuminated by x rays, of the variations in thickness and magnetization across the entire area of the disks. This averaged magnetization mapping of the disks served to study their vortex configuration in each of their magnetic layers, determining the average location of the vortex, the chiral symmetry of its magnetic circulation, and the specific locations where the vortex nucleation starts within the disks. Chiral asymmetry appeared in the disks when the field was oriented at an oblique angle with respect to the easy axis of the array. The local magnetic sensitivity of the technique allowed to identify a non-centrosymmetric distribution of the magnetization of the disks that explains the observed chiral asymmetry. Unexpectedly, the magnetic circulation sense of the vortex was the same in both ferromagnetic layers. In addition, the magnetization of the buried layer was different in the descent branch than in the ascent branch of its hysteresis loops., Comment: 13 pages, 16 figures

Soft X-ray magnetic vector tomography has been used to visualize with unprecedented detail and solely from experimental data the 3D magnetic configuration of a ferrimagnetic Gd12Co88/Nd17Co83/Gd24Co76 multilayer with competing anisotropy, exchange and magnetostatic interactions at different depths. The trilayer displays magnetic stripe domains, arranged in a chevron pattern, which are imprinted from the central Nd17Co83 into the bottom Gd12Co88 layer with a distorted closure domain structure across the thickness. Near the top Gd24Co76 layer, local exchange springs with out-of-plane magnetization reversal, modulated ripple patterns and magnetic vortices and antivortices across the thickness are observed. The detailed analysis of the magnetic tomogram shows that the effective strength of the exchange spring at the NdCo/GdCo interface can be finely tuned by GdxCo1-x composition and anisotropy (determined by sample fabrication) and in-plane stripe orientation (adjustable), demonstrating the capability of 3D magnetic visualization techniques in magnetic engineering research., Comment: 23 pages, 7 figures

The sensitivity of Circularly polarized X ray Resonant Magnetic Scattering (CXRMS) to chiral asymmetry has been demonstrated. The study was performed on a 2D array of Permalloy (Py) square nanomagnets of 700 nm lateral size arranged in a chess lattice of 1000 nm lattice parameter. Previous X ray Magnetic Circular Dichroism Photoemission Electron microscopy (XMCD-PEEM) images on this sample showed the formation of vortices at remanence and a preference in their chiral state. The magnetic hysteresis loops of the array along the diagonal axis of the squares indicate a non-negligible and anisotropic interaction between vortices. The intensity of the magnetic scattering using circularly polarized light along one of the diagonal axes of the square magnets becomes asymmetric in intensity in the direction transversal to the incident plane at fields where the vortex states are formed. The asymmetry sign is inverted when the direction of the applied magnetic field is inverted. The result is the expected in the presence of an unbalanced chiral distribution. The effect is observed by CXRMS due to the interference between the charge scattering and the magnetic scattering., Comment: The new revised version corrected some grammatical and orthographic mistakes like "cero" instead of zero and "core vortex" instead of vortex core. Bibliographic entries were modified to have all the same format

The knowledge of how the magnetization looks inside a ferromagnet is often hindered by the limitations of the available experimental methods that are sensitive only to the surface regions or limited in spatial resolution. We report the 3D tomographic reconstruction of the magnetization within a ferromagnetic film of 240 nm in thickness using soft X ray microscopy and magnetic dichroism. The film has periodic magnetic domains forming stripes and closure domains found to be shifted from the stripe array by 1/4 of the period. In addition, the bifurcations of the stripes, which act as inversion nuclei of the magnetization, evidence in 3D meron singularities and Bloch points at the interior of the film. This novel method can be easily extended to magnetic stacks in spintronics applications and other singularities in films., Comment: 13 pages, 4 figures

Magnetic lateral multilayers have been fabricated on weak perpendicular magnetic anisotropy amorphous Nd-Co films in order to perform a systematic study on the conditions for controlled nucleation of topological defects within their magnetic stripe domain pattern. A lateral thickness modulation of period $w$ is defined on the nanostructured samples that, in turn, induces a lateral modulation of both magnetic stripe domain periods $\lambda$ and average in-plane magnetization component $M_{inplane}$. Depending on lateral multilayer period and in-plane applied field, thin and thick regions switch independently during in-plane magnetization reversal and domain walls are created within the in-plane magnetization configuration coupled to variable angle grain boundaries and disclinations within the magnetic stripe domain patterns. This process is mainly driven by the competition between rotatable anisotropy (that couples the magnetic stripe pattern to in-plane magnetization) and in-plane shape anisotropy induced by the periodic thickness modulation. However, as the structural period $w$ becomes comparable to magnetic stripe period $\lambda$, the nucleation of topological defects at the interfaces between thin and thick regions is hindered by a size effect and stripe domains in the different thickness regions become strongly coupled., Comment: 10 pages, 7 figures, submitted to Physical Review B