  In this paper, we employ micromagnetic simulations to study non-adiabatic
stochastic resonance (NASR) excited by spin-transfer torque in a
super-paramagnetic 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.
