Micromagnetic Modelling of Magnetization Dynamics Driven by Spin-Polarized Current : Stability Diagrams and Role of the Non-Standard Effective Field Contributions

The spin-polarized current can exert a torque on the magnetization and if it is large enough can induce reversal or even excite persistent dynamical regimes. Micromagnetic models can be used to describe the general features of the magnetization dynamics driven by the coexistence of an applied field and a spin-polarized current. In particular, magnetostatic coupling (MC) between ferromagnets and also the classical Ampere field have to be taken into account. A systematic study of the effect of these two contributions will be presented. The main results are that the MC always helps the switching from parallel state (PS) to anti-parallel state (APS) and, more precisely, the application of a current, which gives rise to the switching (PS -> APS or vice versa), results in a faster process with MC than without it. Differently, the role of the Ampere field depends on the physical and geometric properties of the system under investigation and it has to be investigated in each case. The simulations reveal a complex switching behaviour that involves highly inhomogeneous magnetization configurations with multiple domains. Lastly, in order to describe the full behaviour of the magnetization dynamics in these multilayer structures, some complete dynamical stability diagrams have been computed