Current-driven microwave oscillations in current perpendicular-to-plane spin-valve nanopillars

We study the current and temperature dependences of the microwave voltage emission of spin-valve nanopillars subjected to an in-plane magnetic field and a perpendicular-to-plane current. Despite the complex multilayer geometry, clear microwave emission is observed for current densities in the interval of 9x10(7)-13x10(7) A cm(-2). The emission frequency stays near 12 GHz when I < I-red=11.2x10(7) A cm(-2), then redshifts with a slope gradually reaching -350 MHz/mA for 16x10(7) A cm(-2). The linewidth narrows exponentially to 3.8 MHz at 150 K for I < I-red, then broadens again as the emitted voltage redshifts. The temperature dependence of the linewidth exhibits a curvature change around the linewidth minimum.(c) 2006 American Institute of Physics.