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Physics Seminar

Advanced x-ray characterization of novel topological spin textures

Speaker: Peter Fischer (Lawrence Berkeley National Laboratory)
Date: Wednesday 3 November 2021
Time: 15:00
Venue: Zoom

Spin textures and their dynamics hold the key to understand and control the properties, behavior and functionalities of novel magnetic materials, which can impact the speed, size and energy efficiency of spin driven technologies. Topology, frustration, and bespoke geometries that impact spin textures have recently attracted significant scientific interest and led to intense research addressing a broad spectrum of challenging scientific and technological questions, including stability, dynamics, nucleation, and transport in novel spin textures, such as chiral bobbers, magnetic hopfions and torons, skyrmion tubes, and curvilinear magnetism [1].

Advanced characterization tools that provide magnetic sensitivity to spin textures, disentangling the role of individual components in heterogeneous material at high spatial resolution, ultimately at buried interfaces and in all three dimensions [2], and at high temporal resolution to capture the spin dynamics across scales, are required to address those questions, and are therefore of large scientific interest.

Various magnetic soft X-ray spectro-microscopies [3] using polarized soft x-rays 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 [4] or x-ray photo-correlation spectroscopy (XPCS) [5] 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 address static properties and dynamic behavior of various magnetic skyrmion [6,7] and Hopfion [8] textures with potential application to novel magnetic logic and storage devices, and will include 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 [5].

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).

[1] C.H. Back, et al, J Phys D: Appl Phys 53 (36), 363001 (2020)
[2] P. Fischer et al, APL Materials 8 010701 (2020)
[3] P. Fischer and H. Ohldag, Report on Progress in Physics 78 094501 (2015)
[4] X. Shi, et al, Appl Phys Letter 108, 094103 (2016)
[5] M. H. Seaberg, et al, Phys Rev Lett 119 067403 (2017)
[6] S. Woo, et al., Nature Materials 15 501 (2016)
[7] N. Kent et al, Appl Phys Lett 115 112404 (2019)
[8] N. Kent et al, Nature Comm 12 1562 (2021)

Short bio: Dr. Peter Fischer received his PhD in Physics (Dr.rer.nat.) from the Technical University in Munich, Germany in 1993 on pioneering work with X-ray magnetic circular dichroism in rare earth systems and his Habilitation from the University in Würzburg, Germany in 2000 based on his pioneering work on Magnetic Soft X-ray microscopy. Since 2004 he is with the Materials Sciences Division (MSD) at Lawrence Berkeley National Laboratory in Berkeley CA. He is Senior Scientist and Principal Investigator in the Non-Equilibrium Magnetic Materials Program and serves as Deputy Division Director at MSD. His research program is focused on the use of polarized synchrotron radiation for the study of fundamental problems in magnetism. Since 2014 he is also Adjunct Professor for Physics at the University of California in Santa Cruz. Dr. Fischer has published so far about 220 peer reviewed papers and has given more than 320 invited presentations at national and international conferences. He was nominated as Distinguished Lecturer of the IEEE Magnetics Society in 2011. For his achievements of “hitting the 10nm resolution milestone with soft X-ray microscopy” he received the Klaus Halbach Award at the Advanced Light Source in 2010. Dr. Fischer is Fellow of the APS and IEEE.