Spin-Hall-effect-modulation skyrmion oscillator

Hyun-Seok Whang,Sug-Bong Choe

doi:10.1038/s41598-020-68710-y

Abstract

The electric-current-induced spin torque on local magnetization allows the electric control of magnetization, leading to numerous key concepts of spintronic devices. Utilizing the steady-state spin precession under spin-polarized current, a nanoscale spin-torque oscillator tunable over GHz range is one of those promising concepts. Albeit successful proof of principles to date, the spin-torque oscillators still suffer from issues regarding output power, linewidth and magnetic-field-free operation. Here we propose an entirely new concept of spin-torque oscillator, based on magnetic skyrmion dynamics subject to lateral modulation of the spin-Hall effect (SHE). In the oscillator, a skyrmion circulates around the modulation boundary between opposite SHE-torque regions, since the SHE pushes the skyrmion toward the modulation boundary in both regions. A micromagnetic simulation confirmed such oscillations with frequencies of up to 15 GHz in media composed of synthetic ferrimagnets. This fast and robust SHE-modulation-based skyrmion oscillator is expected to overcome the issues associated with conventional spin-torque oscillators.

Highlights

The electric-current-induced spin torque on local magnetization allows the electric control of magnetization, leading to numerous key concepts of spintronic devices
An enhanced output power with a much narrower linewidth has been attained by a spin-torque vortex oscillator (STVO)[16,17], which utilizes the gyration of a vortex core, confined within a point contact
We propose a new spin-torque oscillator—namely, the spin-Hall-effect-modulation skyrmion oscillator (SHEM-SO)—utilizing skyrmion motion directly driven by the horizontal spin-Hall effect (SHE) current

Summary

Introduction

The electric-current-induced spin torque on local magnetization allows the electric control of magnetization, leading to numerous key concepts of spintronic devices. Despite a successful demonstration of its high oscillation frequency with wide-ranging tunability[5,9,10,11,12], the STNOs still require improvement of their output power and linewidth, as well as their method of magneticfield-free operation[13] To overcome these issues, techniques such as synchronization between multiple point contacts[14] and self-injection locking[15] have been investigated. These issues can be solved by introducing current-in-plane (CIP) geometry, which enables easy separation of the detecting and driving current channels and reduces the cross-sectional area of the driving current channel In this sense, we propose a new spin-torque oscillator—namely, the spin-Hall-effect-modulation skyrmion oscillator (SHEM-SO)—utilizing skyrmion motion directly driven by the horizontal SHE current. A SFi system, we demonstrate that the SHEM-SO produces a high frequency comparable to the STNOs, while maintaining all the other merits including the narrow linewidth of the STVOs

Methods

Results

Conclusion