Spin-Transfer and Current-Induced Spin Dynamics in Spin Valves: Diffusive Transport Regime
Current-induced dynamics observed in point contacts or in spin valve structures is one of the most challenging concepts that can bring these nanomagnetic systems toward direct applications. The most promising applications are the nonvolatile memories and nano-oscillators which can be used in telecommunications. Despite the clear application proposals, the full understanding of the microscopic mechanism of current-induced spin dynamics is still an open question. The transfer of angular momentum from conduction electrons to local magnetization is the key microscopic effect. In this chapter, we describe the spin transfer in layered metallic systems (spin valves) and current-induced dynamics via the spin transfer. We present the relation between the normal and inverse current-induced switching, and normal and inverse current-perpendicular-to-plane giant magnetoresistance CPP-GMR. It turns out that these effects are related to the ferromagnet–normal-metal interface asymmetries that in some cases may lead to a nonstandard angular dependence of the spin transfer torque. We also present analysis of the current-induced dynamics within the macrospin model for standard spin valves as well as for asymmetric valves that have nonstandard angular dependence of spin-transfer torque. The asymmetric spin valves are promising candidates for current-induced microwave nano-oscillators in zero magnetic field.
This work, as part of the European Science Foundation EUROCORES Programme SPINTRA, was supported by funds from the Ministry of Science and Higher Education as a research project in years 2006–2009 and the EC Sixth Framework Programme, under Contract N. ERAS-CT-2003-980409. The work was also supported by Slovak Ministry of Education within the project MVTS POL/SR/UPJS/07 and Slovak Grant Agency VEGA under Grant No. 1/2009/05.
- 8.I.A. Campbell, A. Fert: Transport Properties of Ferromagnets. In: Ferromagnetic Materials,Vol. 3, ed by E.P. Wohlfarth, North-Holland, Amsterdam (1982), pp 747–804Google Scholar
- 13.M. Tsoi, J.Z. Sun, M.J. Rooks et al., Phys. Rev. B 69, 100406(R) (2004)Google Scholar
- 37.W.P. Pratt, private communicationGoogle Scholar
- 47.A. Vedyayev97, N. Ryzhanova, B. Dieny et al., Phys. Rev. B 55, 3728–3733 (1997)Google Scholar
- 50.S. Wiggins: Introduction to Applied Nonlinear Dynamical Systems and Chaos, Springer, New York, (1990) pp 35–36Google Scholar
- 51.G. Bertotti, C. Serpico, I.D. Mayergoyz et al., Phys. Rev. Lett. 94, 127206 (200)Google Scholar