Magnetization dynamics in spin torque nano-oscillators: Vortex state versus uniform state

Abstract

Current-driven magnetization dynamics in spin torque nano-oscillators (STNOs) is intensely investigated because of its high potential for high-frequency (HF) applications. We experimentally study current-driven HF excitations of STNOs for two fundamental magnetization states of the free layer, namely, vortex state and uniform in-plane magnetization. Our ability to switch between the two states in a given STNO enables a direct comparison of the critical currents, agility, power, and linewidth of the HF output signals. We find that the vortex state has some superior properties, in particular, it maximizes the emitted HF power and shows a wider frequency tuning range at a fixed magnetic field.