Current-Driven Magnetoresistance Oscillations in Asymmetric Spin Valves

Within the macroscopic model we have calculated spin-transfer torque in asymmetric spin valves in the diffusive transport limit.Such systems exhibit a non-standard angular dependence of the torque, which leads to current-induced precessional modes at zero external magnetic field. We have found that the frequency of magnetoresistance oscillations exhibits hysteretic behavior when the system is driven between two steady precessional regimes. A finite temperature can suppress the irreversibility and give rise to bistable regime where, both the precessional regimes coexist.