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PGI Kolloquium:

Prof. Dr. Pietro Gambardella,
Department of Materials, ETH Zurich, Switzerland

PGI Lecture Hall, Building 04.8, 2nd Floor, Room 365

05.12.2014 11:00 Uhr

Spin-orbit torques and related phenomena in heavy metal/ferromagnetic layers

The interaction between spin and orbital magnetism is responsible for some of the most basic and important magnetic phenomena, such as the magnetocrystalline anisotropy and the anisotropic magnetoresistance. These effects become prominent in thin films and interfaces due to the reduced coordination and the possibility of combining high-Z elements with 3d magnetic compounds. By locking the spin to the direction of motion, the spin-orbit interaction can additionally give rise to nonequilibrium spin accumulation in ferromagnetic/heavy metal bilayers driven by an applied electric field.

The spin Hall effect and the Rashba effect are model illustrations of such phenomena, which result in spin-orbit torques (SOT) acting on the magnetization of the ferromagnetic layer that are strong enough to induce magnetization reversal [1-3]. The in-plane current injection geometry allows for fabricating three-terminal magnetic tunnel junction devices [4] and achieves ultrafast switching with a minimum delay time [5], thus opening an alternative path for developing MRAM that combine reliable and low-energy writing with short read/write access time.

In this talk I will present an overview of these results and discuss several aspects of SOT and unusual magnetoresistive effects in ferromagnetic/heavy metal layers that remain to be clarified.

[1] Current-driven spin torque induced by the Rashba effect in a ferromagnetic metal layer, I. M. Miron, G. Gaudin, S. Auffret, B. Rodmacq, A. Schuhl, S. Pizzini, Jan Vogel, and P. Gambardella, Nature Mater. 9, 230 (2010).
[2] Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection, I. M. Miron, K. Garello, G. Gaudin, P.-J. Zermatten, M. V. Costache, S. Auffret, S. Bandera, B. Rodmacq, A. Schuhl, and P. Gambardella, Nature 476, 189 (2011).
[3] Symmetry and magnitude of spin-orbit torques in ferromagnetic heterostructures, K. Garello, I. M. Miron, C. O. Avci, F. Freimuth, Y. Mokrousov, S. Blügel, S. Auffret, O. Boulle, G. Gaudin, and P. Gambardella, Nature Nanotech. 8, 587 (2013).
[4] Spin-orbit torque magnetization switching of a three terminal perpendicular magnetic tunnel junction, M. Cubukcu, M. Drouard, O. Boulle, K. Garello, C.O. Avci, I. M. Miron, J. Langer, B. Ockert, P. Gambardella, G. Gaudin, Appl. Phys. Lett. 104, 042406 (2014).
[5] Ultrafast magnetization switching by spin-orbit torques, K. Garello, C. O. Avci, I. M. Miron, M. Baumgartner, A. Ghosh, S. Auffret, O. Boulle, G. Gaudin, P. Gambardella, Appl. Phys. Lett. 105, 212402 (2014).


Dr. Gustav Bihlmayer
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