YIG/Permalloy spin torque oscillator

We grow 20 nm thick epitaxial YIG films on GGG substrates and deposit 5 nm Py capping layers, using sputter deposition. Nanowires of 280 nm width and 2.2 μm length are fabricated using single-step e-beam lithography and ion-milling. We investigate the spin-wave spectrum of the nanowires using spin-torque ferromagnetic resonance and micromagnetic simulations. By applying a direct bias current to the nanowire, magnetic damping can be tuned by injecting spin current from the Py layer. We discover that with increasing bias current, the damping can be fully compensated in this system. Above a critical current, the nanowire enters the auto-oscillatory regime and emits a microwave signal. We find that using Py as a spin injector allows us to achieve microwave emission power levels (pW-scale) that significantly exceed those observed in the YIG/Pt systems (fW-scale). We discuss the physics of current-driven auto-oscillatory dynamics, spin-orbit and thermal spin torques in nanodevices based on bi-layer ferromagnets.