  The magnetization evolution of the free layer in an orthogonal spin-torque
device is studied based on a macrospin model. The trajectory of magnetization
vector under various conditions has shown rich nonlinear properties. The phase
diagram is obtained in the parameter spaces of current density and the
polarization distribution (the ratio of in-plane and out-of-plane polarizers).
These dynamic phases can be classified according to their nonlinear behaviors
which are topologically different, namely limit point and/or limit cycle. The
topological classification is meaningful to design the ultra-fast spin-torque
devices under different dynamic conditions towards various applications such as
memory and oscillators.
