Dynamic Phase Diagram of an Orthogonal Spin Torque device: Topological Category
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.