Current-driven magnetization dynamics and their correlation with magnetization configurations in perpendicularly magnetized tunnel junctions

TL;DR

This study investigates the magnetization dynamics in perpendicular magnetic tunnel junctions driven by spin-transfer torque, revealing distinct behaviors of free and reference layers and their potential for neuromorphic computing applications.

Contribution

It demonstrates the different dynamic behaviors of free and reference layers in MTJs and their crossover phenomena, advancing understanding of spin-wave modes in these systems.

Findings

The free layer supports a single coherent spin-wave mode in both configurations.

The reference layer exhibits spin-wave excitation only in the antiparallel state.

A crossover in oscillation frequency with increasing magnetic field was observed.

Abstract

We study spin-transfer-torque driven magnetization dynamics of a perpendicular magnetic tunnel junction (MTJ) nanopillar. Based on the combination of spin-torque ferromagnetic resonance and microwave spectroscopy techniques, we demonstrate that the free layer (FL) and the weak pinned reference layer (RL) exhibit distinct dynamic behaviors with opposite frequency vs. field dispersion relations. The FL can support a single coherent spin-wave (SW) mode for both parallel and antiparallel configurations, while the RL exhibits spin-wave excitation only for the antiparallel state. These two SW modes corresponding to the FL and RL coexist at an antiparallel state and exhibit a crossover phenomenon of oscillation frequency with increasing the external magnetic field, which could be helpful in the mutual synchronization of auto-oscillations for SW-based neuromorphic computing.