Lawrence Berkeley National Laboratory
X-raying non-trivial spin textures
Spin textures are the foundation of properties and behavior of magnetic materials and drive the functionality of magnetic devices. Topology and frustration that impact spin textures have recently attracted significant scientific interest and led to intense research e.g. in magnetic skyrmions (Sk) and artificial spin ice systems (ASI) addressing a broad spectrum of challenging scientific and technological questions, including stability, dynamics, nucleation, and transport. So far, SK and ASI have been treated foremost as two-dimensional spin textures, however, recent investigations have opened the door to a conceptually next leap, which are three-dimensional nanoscale size magnetic spin textures (3D-spin-textures) e.g., chiral bobbers, magnetic hopfions, and skyrmion tubes.
Advanced characterization tools that provide magnetic sensitivity to spin textures at high spatial resolution, ultimately at buried interfaces and in all three dimensions , and at high temporal resolution to capture the spin dynamics across scales, are therefore of large scientific interest. Magnetic soft X-ray spectro-microscopies  provide unique characterization opportunities to study the statics and dynamics of spin textures in magnetic materials combining X-ray magnetic circular dichroism (X-MCD) as element specific, quantifiable magnetic contrast mechanism with spatial and temporal resolutions down to fundamental magnetic length, time, and energy scales. Current developments of x-ray sources aim to increase dramatically the coherence of x-rays opening the path to new techniques, such as ptychography  or x-ray photo-correlation spectroscopy (XPCS)  that allow unprecedented studies of nanoscale heterogeneity, complexity, and fluctuations.
I will review recent achievements and future opportunities with magnetic x-ray spectro- microscopies. Examples will include static properties and dynamic behavior of various magnetic skyrmion [5-7] textures with potential application to novel magnetic logic and storage devices, as well as results from an XPCS study at LCLS with a novel 2-pulse scheme that allowed to discover an unexpected and drastic change of the correlation times in nanoscale spin fluctuations near phase boundaries, i.e., in the skyrmion phase, and near the boundary with the stripe phase of a multilayered Fe/Gd system .
Finally, I will present a study on ferromagnetic liquid droplets, which could establish a complete paradigm shift in magnetic materials, that combine characteristics of liquid, such as reconfigurability and short range spatial and temporal correlations with ferromagnetism, which so far has been confined to condensed matter .
This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division Contract No. DE-AC02-05- CH1123 in the Non-Equilibrium Magnetic Materials Program (MSMAG).
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