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Seminar
Topological Spin Dynamics
Speaker Prof. Mathias Kläui, Johannes Gutenberg-Universität Mainz
Date 12 January 2018 (Friday)
Time 16:30 - 18:00
Venue Lecture Theatre H (Lifts 25-26), HKUST
Abstract

In our information-everywhere society IT is a major player for energy consumption. Novel spintronic devices can play a role in the quest for GreenIT if they are stable and can transport and manipulate spin with low power. Devices have been proposed, where switching by energy-efficient approaches, such as spin-polarized currents is used [1], for which we develop new highly spin-polarized materials and characterize the spin transport using THz spectroscopy [2].

Firstly to obtain ultimate stability, topological spin structures that emerge due to the Dzyaloshinskii-Moriya interaction (DMI) at structurally asymmetric interfaces, such as chiral domain walls and skyrmions with enhanced topological protection can be used [3-5]. We have investigated in detail their dynamics and find that it is governed by the topology of their spin structures [3]. By designing the materials, we can even obtain a skyrmion lattice phase as the ground state of the thin films [4].

Secondly, for ultimately efficient spin manipulation, we use spin-orbit torques, that can transfer more than 1ħ per electron by transferring not only spin but also orbital angular momentum. We combine ultimately stable skyrmions with spin orbit torques into a skyrmion racetrack device [4], where the real time imaging of the trajectories allows us to quantify the novel skyrmion Hall effect [5].

Finally to obtain efficient spin transport, we study graphene and low damping ferro- and antiferromagnetic insulators as spin conduits for long distance spin transport [6] and explore the superfluid spin current regime in antiferromagnets [7]. We find that we can control magnonic spin currents by a newly developed magnon spin valve device [8].

 

Reference

[1] Reviews: O. Boulle et al., Mater. Sci. Eng. R 72, 159 (2011); G. Finocchio et al., J. Phys. D: Appl. Phys. 49, 423001 (2016); A. Bisig et al., PRL 117, 277203 (2016)

[2] M. Jourdan et al., Nature Commun. 5, 3974 (2014);Z. Jin et al., Nature Phys. 11, 761 (2015).

[3] F. Büttner et al., Nature Phys. 11, 225 (2015).

[4] S. Woo et al, Nature Mater. 15, 501 (2016).

[5] K. Litzius et al., Nature Phys. 13, 170 (2017).

[6] A. Kehlberger et al., Phys. Rev. Lett. 115, 096602 (2015);S. Geprägs et al., Nature Commun. 7, 10452 (2016).

[7] Y. Tserkovnyak and M. Kläui, arxiv:1707.01082

[8] J. Cramer et al., arxiv:1706.07592

DEPARTMENT OF PHYSICS