PGI-1 Seminar: Dr. Karin Everschor
Current-Induced Dynamics of Chiral Magnetic Structures
- 13 Jun 2012 11:30
University of Köln
Skyrmions, Emergent Electrodynamics and Spin-Transfer Torques
In magnets without inversion symmetry weak spin-orbit coupling leads to the formation of smooth twisted magnetic structures like helices with a long period. In 2009, a new chiral magnetic phase was observed in the helimagnet manganese silicide (MnSi) which turned out to be a lattice of skyrmions (topologically stable whirl-lines). Since then skyrmion phases in chiral magnets have been observed in several other materials, ranging from metals, semi-conductors and even to insulators. The peculiar winding of the magnetization in the skyrmion lattice phase leads to a very ecient coupling to electric currents with critical current densities which are about 5 orders in magnitude smaller compared to other present-day spin-torque eects like domain wall motion. Electrons traversing a spatially or temporally inhomogeneous magnetization conguration pick up a Berry phase which, can be rewritten as an Aharonov-Bohm phase originating from emergent magnetic and electric elds acting on the electrons. On the other hand, the electric current induces forces on the magnetic texture. We study the current-induced dynamics of skyrmions, i.e. the translational motion as well as rotations of the topologically stable knots within the frame work of the Landau-Lifshitz-Gilbert equation extended by extra damping terms in combination with a phenomenological treatment of pinning forces to develop a theory of the relevant forces and rotational torques.
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