Self-Injection Locking of a Spin Torque Nano-Oscillator to Magnetic Field Feedback

We demonstrate the self-synchronization of a spin torque nano-oscillator (STNO) using magnetic field feedback. The rf output of the STNO is connected to a waveguide which rests on top of the magnetic tunnel junction (MTJ). The resulting rf current flowing through the waveguide creates a magnetic field on the free layer of the MTJ, which acts as the feedback. We observe a large improvement in the quality factor as the feedback strength is increased. Our results indicate a transition to an oscillatory state dominated by feedback at higher feedback strength. We also explore the effect of feedback phase on magnetization oscillation by inserting an adjustable delay in the feedback path. The experimental results are qualitatively supported by macromagnetic simulation. Our results open an alternative avenue to control the magnetization dynamics of a nanomagnet