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23 May 2005 Magnetization dynamics driven by spin momentum transfer (Invited Paper)
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Proceedings Volume 5843, Fluctuations and Noise in Materials II; (2005)
Event: SPIE Third International Symposium on Fluctuations and Noise, 2005, Austin, Texas, United States
A spin-polarized dc current can induce steady-state, microwave frequency magnetization dynamics in a nanoscale ferromagnet. The torque that drives these dynamics originates from the exchange of spin angular momentum between conduction electrons and the magnetization. We present measurements of current perpendicular to the plane (CPP) giant magnetoresistance (GMR) nanopillar devices in which this phenomenon occurs. We focus on devices that contain one reference ferromagnetic layer that has a fixed magnetization and one free ferromagnetic layer with a magnetization that responds to spin torque. The resulting spin transfer induced magnetization dynamics combined with GMR lead to resistance noise, which we measure in both the frequency- and time-domain. The appearance of these dynamical states is consistent with spin transfer in that dynamics are observed only for those combinations of current direction and magnetic configuration in which spin torque opposes the FL configuration set by the magnetic field. Furthermore, the amplitude of the resultant resistance noise increases rapidly with increasing current until saturating at a value that is a large fraction of the magnetoresistance between parallel and antiparallel states. This behaviour is contrasted with similar measurements of a current-in-plane (CIP) GMR device in which the magnetic resistance noise is thermally activated.
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Mark Covington, Y. Yang, T. M. Crawford, N. J. Gokemeijer, and Michael A. Seigler "Magnetization dynamics driven by spin momentum transfer (Invited Paper)", Proc. SPIE 5843, Fluctuations and Noise in Materials II, (23 May 2005);

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