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 9×107–13×107Acm−2. The emission frequency stays near 12GHz when I<Ired=11.2×107Acm−2, then redshifts with a slope gradually reaching −350MHz∕mA for 16×107Acm−2. The linewidth narrows exponentially to 3.8MHz at 150K for I<Ired, then broadens again as the emitted voltage redshifts. The temperature dependence of the linewidth exhibits a curvature change around the linewidth minimum.