Analytical investigation of spin-transfer dynamics using a perpendicular-to-plane polarizer

We studied current-induced magnetic switching and excitations in structures comprising a free layer with in-plane magnetization traversed by a current with perpendicular-to-plane spin polarization. We derived analytical solutions from the Landau–Lifshitz–Gilbert equation including the spin-torque term, and compared them to numerical simulations within the single domain assumption. Taking into account the criterion of thermal stability, the magnetization switching in nanostructures of typical size below 100nm comprising a perpendicular polarizer is found to require larger current density but to be much faster than with a longitudinal polarizer. Furthermore, a steady precession of magnetization can be generated in this geometry; those frequencies can be tuned from about 1 to 20GHz by only changing the current without applying any external field. This opens a promising application as microwave sources.