Periodic structure of spin-transfer current in ferromagnetic multilayers

Abstract

We show that the drift-diffusion mechanism in a normal-metal layer in combination with the resonance electron-magnon interactions at ferromagnet-normal interface of F-N-F heterostucture creates spatial instability modes and, out of these modes, a quasi-stable periodic structure of spin-transfer d.c. current can arise with certain channel step and step-to-radius ratio. The ferromagnetic resonance conditions determine spin-transfer current density. Independent nano-oscillators creating intersecting arrays of channels can phase-lock on sub-micrometer distance, which depends on multilayer geometry and applied fields. By decreasing the layer thickness, the number of channels affected by each independent d.c.-current source and their radius may be diminished. Phase-locking of multiple independent nano-oscillators can be used for enhancement of output power.