Spin-current induced magnetic excitations in single magnetic layer nanopillars*

We investigate current-induced spin-wave excitations in Cu/Co/Cu single magnetic layer nanopillar devices with asymmetric Cu leads by means of transport and microwave probes at room temperature. The thin film stack is deposited by MBE in prefabricated nanostencil masks with lateral dimensions below 100 nm. At high current densities, we observe narrow excitations (bandwidth $\sim $ 100MHz) and higher harmonics for magnetic fields perpendicular to the layers. The frequency increases with increasing current and magnetic field, which indicates an out-of plane precessional mode as found in bilayer systems (e.g., Kiselev et al., PRL 93, 036601(2004)). Furthermore, we observe frequency jumps as a function of both current and magnetic field, which might originate from transitions between different localized nonlinear spin-wave modes.