  In a ferromagnet/heavy-metal bilayer device with strong spin Hall effect an
in-plane current excites magnetic dynamics through spin torque. We analyze
bilayers with perpendicular magnetization and calculate three-dimensional phase
diagrams describing switching by external magnetic field at a fixed current. We
then concentrate on the case of a field applied in the plane formed by the film
normal and the current direction. Here we analytically study the evolution of
both the conventional "up"/"down" magnetic equilibria and the additional
equilibria created by the spin torque. Expressions for the stability regions of
all equilibria are derived, and the nature of switching at each critical
boundary is discussed. The qualitative picture obtained this way predicts
complex hysteresis patterns that should occur in bilayers. By analyzing the
phase portraits of the system we show that when the spin torque induced
equilibrium exists, switching between "up" and "down" states proceeds through
it as an intermediate state. Using numeric simulations we analyze the switching
time and compare it to that of a conventional spin torque device with collinear
magnetizations of the polarizer and the free layer.
