Towards mutual synchronization of serially connected Spin Torque Oscillators based on magnetic tunnel junctions

TL;DR

This paper investigates the synchronization of spin-torque oscillators based on magnetic tunnel junctions, demonstrating experimental methods and conditions for mutual synchronization, and exploring series connection to enhance performance.

Contribution

It provides experimental insights into synchronizing magnetic tunnel junction oscillators using external microwave signals and series connections, addressing fabrication variability challenges.

Findings

Optimal synchronization conditions identified with external microwave source.

Series connection of junctions can improve oscillation power.

Numerical simulations match experimental synchronization conditions.

Abstract

Multiple neuromorphic applications require the tuning of two or more devices to a common signal. Various types of neuromorphic computation can be realized using spintronic oscillators, where the DC current induces magnetization precession, which turns into an AC voltage generator. However, in spintronics, synchronization of two oscillators using a DC signal is still a challenging problem because it requires a certain degree of similarity between devices that are to be synchronized, which may be difficult to achieve due to device parameter distribution during the fabrication process. In this work, we present experimental results on the mechanisms of synchronization of spin-torque oscillators. Devices are based on magnetic tunnel junction with a perpendicularly magnetized free layer and take advantage of a uniform magnetization precision in the presence of the magnetic field and a DC bias. By using an external microwave source, we show the optimal condition for the synchronization of the magnetic tunnel junctions. Finally, we present results on the in-series connection of two junctions and discuss the possible path towards improving oscillation power and linewidth. In addition, using numerical simulations of the coupled oscillators model, we aim to reproduce the conditions of the experiments and determine the tolerance for achieving synchronization.