Micromagnetic understanding of stochastic resonance driven by spin-transfer-torque

In this paper, we employ micromagnetic simulations to study nonadiabatic stochastic resonance (NASR) excited by spin-transfer-torque in a superparamagnetic free layer nanomagnet of a nanoscale spin valve. We find that NASR dynamics involves thermally activated transitions among two static states and a single dynamic state of the nanomagnet and can be well understood in the framework of Markov chain rate theory. Our simulations show that a direct voltage generated by the spin valve at the NASR frequency is at least one order of magnitude greater than the dc voltage generated off the NASR frequency. Our computations also reproduce the main experimentally observed features of NASR such as the resonance frequency, the temperature dependence, and the current bias dependence of the resonance amplitude. We propose a simple design of a microwave signal detector based on NASR driven by spin-transfer-torque.