Spin-transfer-induced magnetic excitation: The role of spin-pumping induced damping

Spin-transfer-induced magnetic excitation in large magnetic field applied perpendicular to the thin film junction surface reveals both a current threshold Ic and a voltage threshold. The current threshold follows the Slonczewski-type of magnetic field dependence [J. C. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996)]. The voltage step at Ic is ΔV which appears to scale with the applied field with a prefactor of the order of 2 μB e, suggesting a threshold to magnetic excitation. Furthermore, experimentally it is observed that ΔV≈ Ic δR, where δR is the magnetoreistance between the parallel and the antiparallel states. This apparent coincidence can be unified when one includes the effect of spin-pumping-related nonlocal damping. The spin-pump damping relates magnetic instability threshold Ic to δR, producing (d Ic dH) δR that is about 2 μB e, explaining the origin of the coincidence. © 2005 American Institute of Physics.