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Controlling the magnetic state with electricity

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The magnetisation of a uniform spin-orbit coupled ferromagnet can be controlled by an electrical current. This spin-orbit torque phenomenon was predicted by theory [1,2] and has been observed in the ferromagnetic semiconductor (Ga,Mn)As [3,4]. Controversial experiments report spin-orbit torques in multilayers of ferromagnetic metals [5,6]. I will describe how the magnetisation of (Ga,Mn)As responds to a microwave electrical current. By electrically exciting ferromagnetic resonance, it is possible to reveal the spin-orbit torque vector [4]. Our experiments aim to understand the symmetries involved and to demonstrate the ‘spin-orbit dynamo’ effect: the precessing magnetisation in such a ferromagnetic layer is predicted to drive an electrical current. I will argue that studying the (Ga,Mn)As model system is essential for the understanding of spin-orbit torques in ferromagnetic metal multilayers. Motivated by the theoretical literature (e.g. [7]) on current induced effects in antiferromagnets, as well as by the potential importance of these materials, I plan to translate my group’s work on current induced dynamics in ferromagnets to antiferromagnetic materials. Controlling, and measuring, the antiferromagnetic state with electricity poses considerable technical and material challenges. I detail experimental plans and motivations in this area. [1] I. Garate and A. H. MacDonald, Phys. Rev. B 80 , 134403 (2009). [2] A. Manchon and S. Zhang, Phys. Rev. B 79 , 094422 (2009). [3] A. Chernyshov, M. Overby, X. Liu, J. K. Furdyna, Y. Lyanda-Geller, and L. P. Rokhinson, Nature Phys. 5, 656 (2009). [4] D. Fang, H. Kurebayashi, J. Wunderlich, K. Vyborny, L. P. Zarbo, R. P. Campion, A. Casiraghi, B. L. Gallagher, T. Jungwirth, and A. J. Ferguson, Nature Nanotech. 6, 413 (2011). [5] I. M. Miron, G. Gaudin, S. Auffret, B. Rodmacq, A. Schuhl, S. Pizzini, J. Vogel and P. Gambardella Nat. Mater. 9, 230 (2010). [6] I. M. Miron, K. Garello, G. Gaudin, P-J. Zermatten, M. V. Costache, S. Auffret, S. Bandiera, B. Rodmacq, A. Schuhl and P. Gambardella, Nature 476, 189 (2011). [7] P. M. Haney and A. H. MacDonald, Phys. Rev. Lett. 100, 196801 (2008).

This talk is part of the Special Departmental Seminars series.

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