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Spin pumping is the generation of a spin motive force by time-dependent magnetizations [1], which in linear response is the Onsager reciprocal to the spin transfer torque [2]. Spin pumping manifests itself e.g. by an increased damping in driven heterostructures of ferromagnets and normal metals and increased thermal noise in spin valves. There is growing evidence that the spin Seebeck effect, discovered by Uchida et al. [3] and observed in various ferromagnets, such as the metal Py [1], insulating Yttrium Iron Garnet (YIG) [4], the semiconductor GaAlMn [5] and the Heusler compound Co2MnSi [6] is caused by spin pumping by a non-equilibrium spin wave dynamics induced by a thermal gradient [7,8]. The magnitude of the spin pumping current and spin Seebeck effect is governed by the spin mixing conductance that can be obtained by the spin-dependent scattering matrix of the interface [9]. This talk will focus on the physics of the spin pumping at the interface between a normal metal and a ferromagnet, emphasizing the difference between a transition metal and an insulating ferromagnet as well as strategies to enhance the effect. The reported results have been obtained in collaboration with J. Xiao, K. Xia, X. Jia, K. Uchida, E. Saitoh, and S. Maekawa. This research has been supported by the EU, FOM, and DFG. 1. Y. Tserkovnyak, A. Brataas, and G.E.W. Bauer, Phys. Rev. Lett. 88, 117601 (2002). 2. A. Brataas, Y. Tserkovnyak, G.E.W. Bauer, and P.J. Kelly, in Spin Current (Eds. S. Maekawa. S. Valenzuela, E. Saitoh & T. Kimura), Oxford.University Press, in preparation. 3. K. Uchida et al., Nature 445, 778-781 (2008). 4. K. Uchida et al., Nature Mater. 9, 894 (2010). 5. C.M. Jaworski et al., Nature Mater. 9, 898 (2010). 6. S. Bosu et al., unpublished. 7. J. Xiao et al., Phys. Rev. B 81, 214418 (2010). 8. H. Adachi et al., arXiv:1010.2325. 9. X. Jia, K. Liu, K. Xia, G.E.W. Bauer, arXiv:1103.3764 |
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