Microwave emission power exceeding 10 μW in spin torque vortex oscillator

We fabricated vortex-type spin-torque oscillators (STOs) with optimized structures to enhance the microwave emission power. Inserting a thin Co70Fe30 layer between the MgO tunnel barrier and Fe-B free layer of the STOs resulted in the magnetoresistance ratio up to 190% with a resistance area (RA) value of 4.1 Ω μm2, which contributed to a large enhancement of the emission power. The optimized STO exhibited the emission power of 10.1 μW, which is the highest power from a single STO reported to date, with excellent frequency stability (f STO/Δf = 2000 with the timing jitter of 12 ps). The results suggest that the vortex-STOs are promising candidates for next generation microwave generators.