Spin current induced magnetization oscillations in a paramagnetic disc

TL;DR

This paper proposes a novel method to induce steady-state magnetization oscillations in a paramagnetic disc via spin current injection, leveraging eddy current-generated magnetic torques, with potential applications in spintronics.

Contribution

It introduces a new mechanism for steady-state precession in paramagnets driven by spin current and eddy currents, differing from ferromagnetic spin-torque oscillators.

Findings

Steady-state oscillations can be achieved with sufficient spin injection.

A magnetic field reduces the threshold for oscillation.

The frequency is determined by the disc's dimensions and properties.

Abstract

When electron spins are injected uniformly into a paramagnetic disc, they can precess along the demagnetizing field induced by the resulting magnetic moment. Normally this precession damps out by virtue of the spin relaxation which is present in paramagnetic materials. We propose a new mechanism to excite a steady-state form of this dynamics by injecting a constant spin current into this paramagnetic disc. We show that the rotating magnetic field generated by the eddy currents provide a torque which makes this possible. Unlike the ferromagnetic equivalent, the spin-torque-oscillator, the oscillation frequency is fixed and determined by the dimensions and intrinsic parameters of the paramagnet. The system possesses an intrinsic threshold for spin injection which needs to be overcome before steady-state precession is possible. The additional application of a magnetic field lowers this threshold. We discuss the feasibility of this effect in modern materials. Transient analysis using pump-probe techniques should give insight in the physical processes which accompany this effect.