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Magnetic skyrmions

Professor Thorsten Hesjedal FInstP

Professor of Condensed Matter Physics

Research theme

  • Quantum materials

Sub department

  • Condensed Matter Physics

Research groups

  • Thin film quantum materials
  • Oxford Quantum Institute
  • Magnetism for Intelligent Devices (MIND)
Thorsten.Hesjedal@physics.ox.ac.uk
Telephone: 01865 (2)72235
  • About
  • Publications

Slow Equilibrium Relaxation in a Chiral Magnet Mediated by Topological Defects

(2024)

Authors:

Chenhao Zhang, Yang Wu, Jingyi Chen, Haonan Jin, Jinghui Wang, Raymond Fan, Paul Steadman, Gerrit van der Laan, Thorsten Hesjedal, Shilei Zhang
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Rolling Motion of Rigid Skyrmion Crystallites Induced by Chiral Lattice Torque.

Nano letters American Chemical Society (ACS) (2024)

Authors:

Haonan Jin, Jingyi Chen, Gerrit van der Laan, Thorsten Hesjedal, Yizhou Liu, Shilei Zhang

Abstract:

Magnetic skyrmions are topologically protected spin textures with emergent particle-like behaviors. Their dynamics under external stimuli is of great interest and importance for topological physics and spintronics applications alike. So far, skyrmions are only found to move linearly in response to a linear drive, following the conventional model treating them as isolated quasiparticles. Here, by performing time and spatially resolved resonant elastic X-ray scattering of the insulating chiral magnet Cu2OSeO3, we show that for finite-sized skyrmion crystallites, a purely linear temperature gradient not only propels the skyrmions but also induces continuous rotational motion through a chiral lattice torque. Consequently, a skyrmion crystallite undergoes a rolling motion under a small gradient, while both the rolling speed and the rotational sense can be controlled. Our findings offer a new degree of freedom for manipulating these quasiparticles toward device applications and underscore the fundamental phase difference between the condensed skyrmion lattice and isolated skyrmions.
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Magnetization dynamics driven by displacement currents across a magnetic tunnel junction

Physical Review Applied American Physical Society 22:2 (2024) 24019

Authors:

Safeer Chenattukuzhiyil, Paul S Keatley, Witold Skowroński, Jakub Mojsiejuk, Kay Yakushiji, Akio Fukushima, Shinji Yuasa, Daniel Bedau, Fèlix Casanova, Luis E Hueso, Robert J Hicken, Daniele Pinna, Gerrit van der Laan, Thorsten Hesjedal

Abstract:

Understanding the high-frequency transport characteristics of magnetic tunnel junctions (MTJs) is crucial for the development of fast-operating spintronics memories and radio frequency devices. Here, we present the study of a frequency-dependent capacitive current effect in CoFeB/MgO-based MTJs and its influence on magnetization dynamics using a time-resolved magneto-optical Kerr effect technique. In our device, operating at gigahertz frequencies, we find a large displacement current of the order of mA, which does not break the tunnel barrier of the MTJ. Importantly, this current generates an Oersted field and spin-orbit torque, inducing magnetization dynamics. Our discovery holds promise for building robust MTJ devices operating under high current conditions, also highlighting the significance of capacitive impedance in high-frequency magnetotransport techniques.
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Valence-state mixing and reduced magnetic moment in Fe 3 − δ GeTe 2 single crystals with varying Fe content probed by x-ray spectroscopy

Nanotechnology IOP Publishing 35:39 (2024) 395709

Authors:

D Backes, R Fujita, LSI Veiga, DA Mayoh, GDA Wood, SS Dhesi, G Balakrishnan, G van der Laan, T Hesjedal

Abstract:

We present a spectroscopic study of the magnetic properties of Fe3−δGeTe2 single crystals with varying Fe content, achieved by tuning the stoichiometry of the crystals. We carried out x-ray absorption spectroscopy and analyzed the x-ray circular magnetic dichroism spectra using the sum rules, to determine the orbital and spin magnetic moments of the materials. We find a clear reduction of the spin and orbital magnetic moment with increasing Fe deficiency. Magnetic susceptibility measurements show that the reduction in magnetization is accompanied by a reduced Curie temperature. Multiplet calculations reveal that the Fe2+ state increasingly mixes with a higher valence state when the Fe deficiency is increased. This effect is correlated with the weakening of the magnetic moment. As single crystals are the base material for exfoliation processes, our results are relevant for the assembly of 2D magnetic heterostructures.
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Materials for quantum technologies: a roadmap for spin and topology

(2024)

Authors:

N Banerjee, C Bell, C Ciccarelli, Thorsten Hesjedal, F Johnson, H Kurebayashi, Ta Moore, C Moutafis, Hl Stern, Ij Vera-Marun, J Wade, C Barton, Mr Connolly, Nj Curson, K Fallon, Aj Fisher, Da Gangloff, W Griggs, E Linfield, Ch Marrows, A Rossi, F Schindler, Jason Smith, T Thomson, O Kazakova
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