We theoretically investigate the threshold current for thermally activated
switching of a perpendicular magnet by spin-orbit spin torque. Based on the
Fokker-Planck equation, we obtain an analytic expression of the switching
current, in agreement with numerical result. We find that thermal energy
barrier exhibits a quasi-linear dependence on the current, resulting in an
almost linear dependence of switching current on the log-scaled current
pulse-width even below 10 ns. This is in stark contrast to standard spin torque
switching, where thermal energy barrier has a quadratic dependence on the
current and the switching current rapidly increases at short pulses. Our
results will serve as a guideline to design and interpret switching experiments
based on spin-orbit spin torqueComment: 18 pages, 4 figure
