Soft x-ray microscopy: Facing the mesoscale challenge in magnetism

Abstract

For more than a decade magnetism research focused on a fundamental understanding and controlling of spins on a nanoscale. The next step beyond the nanoscale will be governed by mesoscale phenomena. Those are expected to add complexity and functionality, which are essential design parameters e.g. for the realization of future spintronic devices. Advanced characterization techniques will play key roles in achieving mesoscience goals and multidimensional spectromicroscopies utilizing polarized soft x-rays offering a unique combination of spatiotemporal resolution, elemental and magnetic sensitivity, and tomographic capabilities are very promising. As an example for complex behavior we show experimental results of the stochastic character of the nucleation of magnetic vortex structures in arrays of permalloy nanodisk. We have used magnetic soft x-ray microscopy to image at 25nm spatial resolution and a field of view of about 8 μm diameter both the circularity and the polarity of the disk, which allowed us to categorize the nucleated vortex state without ambiguity. We have found a symmetry breaking effect in the final vortex state, represented by a preferred handedness. We were able to identify as the origin of the asymmetry an internal Dzyaloshinskii-Moriya interaction arising from a broken inversion symmetry at the top and bottom surface/interface of the disk. Full 3-dimensional micromagnetic simulations confirmed our experimental observation. Here we present our observations with regard to disk diameter and disk thickness. Various soft x-ray microscopy approaches are currently pursued to obtain full 3dimensional images of magnetic structures, including computed reconstruction of 2dim projection images. © 2013 Copyright SPIE.