Spin torque nano-oscillator driven by combined spin injection from tunneling and spin Hall current

Spin-transfer torque nano-oscillators (STNO) are important candidates for several applications based on ultra-tunable microwave generation and detection. The microwave dynamics in these STNOs are induced by spin currents that are typically generated either by spin polarization in an adjacent ferromagnetic layer or through the spin Hall effect. In this paper, a 3-terminal STNO based on a magnetic tunnel junction is excited by both of these spin injection mechanisms. The combination of these two mechanisms excites the free layer into dynamic regimes beyond what can be achieved by each excitation mechanism individually, resulting in enhanced output powers, a key figures of merit for device performance. The system response can be coherently quantified as a function of the total injected spin current density. The experimental data shows an excellent consistency with this simple model and a critical spin current density of 4.52 ± 0.18 × 10⁹ħ/2 e⁻¹ Am⁻².