We report on a time-domain study of parametric synchronization in a magnetic tunnel junction based spin torque nano-oscillator (STNO). Time-domain measurements of the instantaneous frequency (fi) of a parametrically synchronized STNO show random short-term unlocking of the STNO signal for low injected radio-frequency (RF) power, which cannot be revealed in time-averaged frequency domain measurements. Macrospin simulations reproduce the experimental results and reveal that the random unlocking during synchronization is driven by thermal fluctuations. We show that by using a high injected RF power, random unlocking of the STNO can be avoided. However, a perfect synchronization characterized by complete suppression of phase noise, so-called phase noise squeezing, can be obtained only at a significantly higher RF power. Our macrospin simulations suggest that a lower temperature and a higher positive ratio of the field-like torque to the spin transfer torque reduce the threshold RF power required for phase noise squeezing under parametric synchronization.
@article{arxiv.1706.06736,
title = {Time-domain stability of parametric synchronization in a spin-torque nano-oscillator based on a magnetic tunnel junction},
author = {Raghav Sharma and Naveen Sisodia and Philipp Dürrenfeld and Johan Åkerman and P. K. Muduli},
journal= {arXiv preprint arXiv:1706.06736},
year = {2017}
}