Dr Axel Hoffmann
University of Illinois Urbana-Champaign, USA
Axel Hoffmann received his Diploma in physics from the RWTH Aachen in 1994 and his PhD in physics from the University of California – San Diego in 1999. Subsequently, he worked at the Los Alamos National Laboratory as a postdoctoral fellow. In 2001 he joined the Argonne National Laboratory as a staff scientist and became in 2014 the Senior Group Leader of the Magnetic Thin Film Group within the Materials Science Division. In 2019 he joined the Department of Materials Science and Engineering at the University of Illinois Urbana-Champaign as a Founder Professor. His research interests encompass various magnetism topics, including magnetic heterostructures, spin-transport, and magnetization dynamics. He has more than 200 publications, five book chapters, four magnetism-related U.S. patents, and edited two books. He is an Associate Editor for the Journal of Applied Physics and a fellow of the American Physical Society, American Vacuum Society, and IEEE. His awards include Distinguished Lecturer for the IEEE Magnetics Society (2011), Outstanding Researcher Award by the Prairie Section of the American Vacuum Society (2015), Highly Cited Researcher by Clarivate (2019–2024), the David Adler Lectureship Award in the Field of Materials Physics from the American Physical Society (2022), and the Research Award by the Alexander von Humboldt Foundation (2024).
Abstract: Unconventional Spin-Orbit Torque
Axel Hoffmann
Department of Materials Science and Engineering and Materials Research Laboratory, University of Illinois Urbana‑Champaign, Urbana, IL 61801, USA
Spin-orbit torques allow very energy-efficient electrical manipulation of magnetization states and provide the key to many modern spintronics developments [1]. Generally, spin-orbit torques originate from electrically generating a spin accumulation in a conducting layer that can be transferred to an adjacent ferromagnetic layer. Ordinarily, due to symmetry considerations, the spin accumulations that provide the torque on the magnetization have spin polarizations that are confined to directions within the interfacial plane and are perpendicular to the electric current directions, which is only suitable for deterministic switching of in-plane magnetizations. However, materials with lower symmetries may also allow unconventional spin-orbit torques, which are suitable for deterministic switching of magnetic layers with perpendicular magnetic anisotropy. I will demonstrate different examples of such unconventional spin-orbit torques, where the symmetries are either reduced through magnetic structures in the metallic antiferromagnets IrMn3 [2] and FeRh [3], or via the crystal structure in CrPt3 [4], MoTe2 [5], and Te.
References:
[1] Q. Shao, et al., IEEE Trans. Magn. 57, 800439 (2021).
[2] J. Holanda, et al., Phys. Rev. Lett. 124, 087204 (2020).
[3] J. Gibbons, et al., Phys. Rev. Appl. 18, 024075 (2022).
[4] R. Klause, et al., Phys. Rev. Appl. 22, 044043 (2024).
[5] S. Li, et al., Phys. Rev. B 110, 024426 (2024).
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