  We theoretically investigate the switching of a perpendicular magnetic layer
by in-plane charge current due to the spin Hall effect. We find that, in the
high damping regime, the threshold switching current is independent of the
damping constant, and is almost linearly proportional to both effective
perpendicular magnetic anisotropy field and external in-plane field applied
along the current direction. We obtain an analytic expression of the threshold
current, in excellent agreement with numerical results. This expression can be
used to determine the physical quantities associated with spin Hall effect, and
to design relevant magnetic devices based on the switching of perpendicular
magnetic layers.
