Injection locking of single-vortex and double-vortex spin-torque oscillators

Spin-torque oscillators are a promising application for the spin-transfer torque effect. The major challenge lies in pushing their microwave output power to useful levels, e. g. by operating an array of spin-torque oscillators in a synchronized, phase-locked mode. Our experiments on metallic, GMR-type nanopillars focus on the influence of external high-frequency signals on the current-driven vortex dynamics in single-vortex and double-vortex spintorque oscillators. For both cases we observe injection locking behavior according to the nonlinear oscillator theory, which is a prerequisite for the synchronization of spin-torque oscillators via microwaves in common electrical electrodes.