Topological spin-torque diode effect in skyrmion-based magnetic tunnel junctions

TL;DR

This paper demonstrates the electrical excitation and detection of skyrmion dynamics in magnetic tunnel junctions at room temperature, enabling a new topological spin torque diode with potential for energy-efficient microwave detection.

Contribution

It introduces a novel topological spin torque diode based on skyrmions in MTJs, showing room-temperature operation and resonant excitation of skyrmion modes.

Findings

Skyrmions can be electrically excited and detected in MTJs at room temperature.

Resonant skyrmion modes occur near 4 GHz with high selectivity.

Micromagnetic simulations reveal the role of magnetic parameters in skyrmion stabilization and excitation.

Abstract

The growing market and massive use of Internet of Things nodes is placing unprecedented demands of energy efficient hardware for edge computing and microwave devices. In particular, magnetic tunnel junctions (MTJs), as main building blocks of spintronic microwave technology, can offer a path for the development of compact and high-performance microwave detectors. On the other hand, the fascinating field of skyrmionics is bridging together concepts from topology and spintronics. Here, we show the proof of concept of the direct electrical excitation and detection of the dynamics of a topological protected magnetic texture, i.e. skyrmion at room temperature and for a wide region of applied fields, including the zero field case. This topological spin torque diode is realized with an MTJ on top of a skyrmionic material. Quantitative Magnetic Force Microscopy measurements are employed to confirm the existence of a single skyrmion in the MTJ free layer. Spin torque diode electrical measurements show the electrical excitation via spin transfer torque (STT) of a skyrmion resonant mode with frequencies near 4 GHz and a selectivity one order of magnitude smaller than the uniform modes excited in the same device. Micromagnetic simulations identify these dynamics with the excitation of the breathing mode and point out the role of thickness dependent magnetic parameters (magnetic anisotropy field and Dzyaloshinkii Moriya interaction) in both stabilizing and exciting the magnetic skyrmions. This work marks a milestone for the development of topological spin torque diodes.