Theoretical analysis of thermally activated spin-transfer-torque switching in a conically magnetized nanomagnet

We theoretically studied spin-transfer-torque switching of a spin-valve nanopillar with a conically magnetized free layer in a thermally activated regime. Starting from the Fokker-Planck equation, analytical expressions of the switching probability P-sw are derived. Under zero external magnetic field, the thermal stability factor is well approximated as Delta(0)(1 - J/J(sw)) 1.53, where J/J(sw) represents the applied current density normalized by the switching current density and Delta(0) represents the thermal stability factor in the absence of current. The results enable us to evaluate Delta(0) of conically magnetized nanomagnet from the observed current dependence of P-sw at ambient temperature.