Linewidth reduction in spin--torque oscillators by delayed self-injection

Spin-torque oscillators offer the possibility of tunable microwave frequency generation in a nanoscale device that is compatible with conventional technology. Hurdles to their regular use have been the large critical current needed to sustain oscillations and a spectral linewidth that is too large for industrial adoption. In this talk we describe our analytic/numerical investigation of linewidth reduction in spin-torque oscillators based on delayed self-injection of the output current. We discuss the general response of the model system for arbitrary delay time which can include: linewidth and frequency variation, the possibility of multiple stable frequencies, and mode-hopping. We present analytic results for the critical current and linewidth and show that this technique can be used for meaningful linewidth reduction with realistic system parameters.