Bias-Field-Free Microwave Oscillator Driven by Perpendicularly Polarized Spin Current

In this paper, we propose a novel design of spin-torque-driven microwave oscillator that is free of bias magnetic field. The oscillator consists of a perpendicularly magnetized spin-polarization layer and an oscillating bilayer. The oscillating bilayer comprises a spin-torque-driven layer and a magnetic layer of perpendicular anisotropy with adequate interlayer-exchange coupling. The perpendicularly spin-polarized current can yield a sustained stable magnetization oscillation in the oscillating bilayer around the perpendicular easy axis. The oscillating frequency can be tuned from zero to tens of gigahertz by varying the inject current density. The underlying physical mechanism of the oscillation is discussed, and a micromagnetic analysis on the characteristics of the oscillator is reported