Vortex nucleation in spin-torque nanocontact oscillators

We present an experimental study of the nucleation rate associated with current-driven vortex oscillations in magnetic nanocontacts. We find that the nucleation and subsequent steady-state oscillation of a vortex can be initiated using current pulses as short as a few nanoseconds, yielding instant on oscillator capability. The nucleation rate is governed by an Arrhenius law, with an exponential dependence on the applied current magnitude. The mechanism for the vortex nucleation is discussed and compared to analytical estimates assuming the transient presence of a vortex-antivortex pair. (C) 2010 American Institute of Physics. [doi:10.1063/1.3478843]