Helical spin-transfer torque nanooscillator

Abstract

We propose an alternative type of spin-transfer torque nanooscillator based on a multilayer cylindrical stack consisting of three ferromagnetic single-domain disks separated by a nonmagnetic metal. The equilibrium states and dynamics of disk magnetization under electric current pumping are investigated by micromagnetic modeling. We show that due to magnetostatic interaction in such a system, a magnetic helix with 120° orientation of magnetic moments in adjacent disks is formed. The electric current pumping generates the coherent rotation of the disks magnetization caused by spin-transfer torque effect without any initial spin polarization of carriers. The peculiarities of the magnetic helix rotation in dependence on the pump current level for stacks with different disk thicknesses and diameters are investigated. In addition, the possibility of experimental implementation of a helical spin–torque nanogenerator is considered, in which the stack is connected to the spin polarization analyzer through a tunnel barrier. We assume that the main advantages of such a generator to be a low excitation threshold, a wide frequency tuning range, and maximum modulation of the magnetoresistance at the tunnel contact.