  We show how the phase diagram for spin torque switching in the case of
perpendicular anisotropy is altered at nonzero temperature. The hysteresis
region in which the parallel and antiparallel states coexist shrinks, and a new
region of telegraph noise appears. In a small sample, the region of coexistence
of a precessional and parallel state can disappear entirely. We show that the
phase diagram for both zero and nonzero temperatures can be understood and
calculated by plotting an effective energy as a function of angle. A
combinatorial analysis is useful for systematically describing the phase
diagram.
