Spin-current driven spontaneous coupling of ferromagnets

Abstract

A theoretical framework is proposed for the spin-current driven synchronized self-oscillations in ferromagnets in the spin Hall geometry. The spin current generated by the spin Hall effect in a bottom nonmagnetic heavy metal excites a self-oscillation of the magnetization in an attached ferromagnet through spin-transfer effect. The spin current simultaneously creates spin accumulation inside the ferromagnet. Therefore, when the top surfaces of two ferromagnets are connected by a nonmagnetic material having a long spin diffusion length, another spin current flows according to the gradient of the spin accumulations between the ferromagnets. This additional spin current excites an additional spin torque leading to a coupled motion of the magnetizations. This coupling mechanism comes purely from spin degree of freedom in the system without using electric and/or magnetic interactions. The additional spin torque acts as a repulsive force between the magnetizations, and prefers an antiphase synchronization between the oscillators. The phase difference in a synchronized state is determined by the competition between this additional spin torque and spin pumping. Eventually, either an in-phase or antiphase synchronization is spontaneously excited in the individual ferromagnets, depending on the current magnitude. These conclusions are obtained by deriving the theoretical formula of the additional spin torque from the diffusive spin transport theory and solving the equation of motion of the magnetizations both numerically and analytically.

19 pages, 8 figures

References in corpus (10)

• Theory of spin Hall magnetoresistance
• Coupling functions: Universal insights into dynamical interaction mechanisms
• Anomalous Bias Dependence of Spin Torque in Magnetic Tunnel Junctions
• Magnetoresistance generated from charge-spin conversion by anomalous Hall effect in metallic ferromagnetic/nonmagnetic bilayers
• Mutual synchronization of spin-torque oscillators consisting of perpendicularly magnetized free layers and in-plane magnetized pinned layers
• Relaxation time and critical slowing down of a spin-torque oscillator
• Dynamic coupling of ferromagnets via spin Hall magnetoresistance
• Mutual synchronization of nano-oscillators driven by pure spin current
• Phase dynamics of oscillating magnetizations coupled via spin pumping
• Current-induced magnetization dynamics in two magnetic insulators separated by a normal metal

Cited by in corpus (3)

• Chaos in nanomagnet via feedback current
• Synchronized, periodic, and chaotic dynamics in spin torque oscillator with two free layers
• Charge conservation in spin torque oscillators leads to a self-induced torque