Dresden 2011 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 31: TR: Nanoelectronics II - Spintronics and Magnetotransport 1 (jointly with HL and MA)

TT 31.8: Talk

Wednesday, March 16, 2011, 12:45–13:00, HSZ 301

Spin transfer torques in chiral magnetic structures — •Karin Everschor¹, Markus Garst¹, Rembert Duine², Achim Rosch¹, Florian Jonietz³, Sebastian Mühlbauer^3,4, Christian Pfleiderer³, Andreas Neubauer³, Wolfgang Münzer³, Andreas Bauer³, Tim Adams³, Robert Georgii^3,4, Peter Böni³, Michael Wagner³, and Tomek Schulz³ — ¹Inst. für Theoretische Physik, Universität zu Köln — ²Inst. for Theoretical Physics, Utrecht University, Netherlands — ³Physik-Department E21, Technische Universität München — ⁴FRM II, Technische Universität München

We investigate the influence of electric currents on magnetic structures in bulk materials. In magnets without inversion symmetry, weak spin-orbit coupling leads to the formation of magnetic helices with a long pitch. These helices pin only weakly to disorder and the underlying crystalline lattice. Another weakly pinned, non inversion symmetric phase is the 2d Skyrmion lattice which appears for example in MnSi. Electrons traversing the topolocially stable knots pick up a Berry phase, which leads to an effective Lorentz force acting on the electrons. Via a "topological" contribution to the Hall effect this Lorentz force can be observed. The counter force, which is a Magnus force, acts together with additional drag forces on the Skyrmion lattice. A gradient in these forces (induced by a small temperature gradient) results in a net torque that can be observed with neutron scattering.

The coupling of the Skyrmion lattice to inhomogeneous spin currents is very efficient, leading to an ultra-low electrical threshold current of j=10⁶ A/m² to observe spin transfer torques.