Interaction of Spin-Transfer Oscillators With AC Currents and Fields

We have shown previously that a DC current flowing through a 40 nm point contact made to a spin valve structure induces high frequency, large-angle coherent magnetic precession.~ The precession frequency ranges from 5-40+ GHz, and is a strong function of the field magnitude and direction, and the current.~ Injection of an additional AC current into the device produces frequency modulation for low injected frequencies, and "injection locking" for injection frequencies near the resonant frequency.~ We will present a detailed analysis of the injection locking process, highlighting the similarities and differences with conventional oscillators, and using the injection locking as a means of determining the precession amplitude at the device.~ In addition, we will show results on the effect of AC magnetic fields on the spin-transfer resonance.~ Comparison with models to describe the effects on the magnetization trajectory will be made.