Time-resolved X-ray Imaging of Spin-Torque-Induced Vortex Oscillation

Recent transport measurements demonstrated a persistent oscillation of a magnetic vortex isolated in a nanoscale spin valve structure driven by a d. c. spin-polarized current [1]. The magnetic information is inferred from the giant magnetoresistance (GMR) signal, which depends on the relative average magnetization of the two magnetic layers. Here, we report spatially resolved measurements of the vortex oscillation driven by spin-transfer torque by using advanced x-ray imaging technique. The microwave-frequency vortex oscillation is synchronized to the fast x-ray pulses. Motion images with 70ps time resolution and 30nm spatial resolution reveal the complicated dynamics underlying the previously observed oscillating GMR signal. [1] V. S. Pribiag, I. N. Krivorotov, G. D. Fuchs, P. M. Braganca, O. Ozatay, J. C. Sankey, D. C. Ralph, and R. A. Buhrman, Nature Physics 3, 498 (2007)