Magnetization oscillations induced by spin current in a paramagnetic disc

When electron spins are injected uniformly into a paramagnetic disk, 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 mechanism to excite a steady-state form of this dynamics by injecting a constant spin current into this paramagnetic disk. We show that the rotating magnetic field generated by the eddy currents provide a torque that 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.