Macroscopic description of magnetic behaviors induced by spin transfer in magnetic multilayer nanostructures

A theoretical study is presented for the magnetic behaviors of a nanostructure consisting of two ferromagnetic (FM) layers separated by a nonmagnetic (NM) layer under the influence of a spin-polarized current. A modified magnetic dynamic equation was developed. The spin accumulation in the FM layer was investigated and the spin polarization factors at the interfaces were obtained by calculating the spin-polarized current of each layer. The injected current not only produces a spin transfer torque, but also alters the effective magnetic field, and thus affects the magnetic damping. The competition between damping and spin accumulation determines the dynamic behaviors of magnetization switching and oscillation. We discussed the conditions and characteristics of irreversible magnetic switching and stable spin precession.