Time:2012-04-11, 10:00am

Venue:Conference Hall 322, Science Building

Title:Spin-transfer torques and emergent electrodynamics in magnetic skyrmion crystals

Speaker:Dr. Markus Garst

Institut für Theoretische Physik, Germany

Universität zu Köln, Germany

Abstract:A Skyrmion crystal -- a lattice of topologically stable magnetic whirls -- can be stabilized in chiral magnets in a finite magnetic field range and it has been identified so far in several metallic compounds like MnSi, FeGe or Fe_{1−x}Co_xSi. Such magnetic skyrmions couple efficiently to spin-currents resulting in observable spintronic phenomena in a bulk material at low current densities of order 10^6 A/m^2. First, a spin-current can induce a finite spatial rotation of the skyrmion lattice [1], which can be understood as a double-transfer of angular momentum: in addition to the usual spin-transfer torque, angular momentum is transferred from the magnetic texture to the ionic crystal lattice giving rise to a mechanical torque resulting in a rotation of the skyrmion lattice. Second, a moving skyrmion lattice leads to artificial electric and magnetic fields that act on the electrons and which were recently detected by Hall Effect measurements [2]. As the electron spin constantly adapts to the skyrmion texture, its orbital motion experiences an artificial magnetic field of one flux quantum per skyrmion. If the applied electric current exceeds a threshold value, the depinning of skyrmions results in a moving magnetic texture that induces an artificial electric field via Farady's law of induction. The resulting emergent artifical electrodynamics promises to become an interesting playground for novel spintronic phenomena.

[1] Spin-Transfer Torques in MnSi at Ultralow Current Densities, F Jonietz, S Mühlbauer, Christian Pfleiderer, A Neubauer, W Münzer, A Bauer, T Adams, R Georgii, P Böni, R. A Duine, K Everschor, Markus Garst, Achim Rosch, Science 330, 1648 (2010).

[2] Emergent electrodynamics of skyrmions in a chiral magnet, T. Schulz, R. Ritz, A. Bauer, M. Halder, M. Wagner, C. Franz, C. Pfleiderer, K. Everschor, M. Garst, and A. Rosch, Nature Physics (2012) doi:10.1038/nphys2231