# Time-domain stability of parametric synchronization in a spin-torque nano-oscillator based on a magnetic tunnel junction

## TL;DR

This study investigates the time-domain behavior of parametric synchronization in a magnetic tunnel junction-based spin-torque nano-oscillator, revealing thermal fluctuation effects and conditions for optimal phase noise reduction.

## Contribution

It provides the first time-domain analysis of parametric synchronization in STNOs, highlighting thermal fluctuation impacts and power thresholds for phase noise squeezing.

## Key findings

- Random short-term unlocking occurs at low RF power due to thermal fluctuations.
- Higher RF power suppresses random unlocking and achieves phase noise squeezing.
- Lower temperature and favorable torque ratios reduce RF power needed for optimal synchronization.

## Abstract

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 ($f_{i}$) 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.