Field-Free Switching of a Spin-Orbit-Torque Device Through Interlayer-Coupling-Induced Domain Walls

Abstract

The spin-orbit torque device is promising as a candidate for next generation magnetic memory, while the static in-plane field needed to induce deterministic switching is a main obstacle for its application in highly integrated circuits. Instead of introducing effective field into the device, in this work we present an alternative way to achieve the field-free current-driven magnetization switching.By adding Tb/Co multilayers at two ends of the current channel, assisting domain wall is created by interlayer exchange coupling. The field-free deterministic switching is achieved by the movement of the domain wall driven by current. By loop shift measurement we find the driven force exerted on the domain wall is determined by the direction of the in-plane moment in the domain wall. Finally, we modify the device into a synthetic antiferromagnetic structure to solve the problem of reading out signal. The present work broadens the choice of field-free spin-orbit torque device design and clearly depicts the difference between two different switching mechanism.

Enhanced Spin–Orbit Torque and Low Critical Current Density in Pt100–xRux/[CoNi]/Ru Multilayer for Spintronic Devices

“…Spin–orbit torque (SOT)-based devices and related researches have become an important field since their discovery in 2011. , Unlike spin-transfer torque (STT) devices, they provide a new approach for switching the magnetization of the ferromagnetic metal (FM) layer via an in-plane current injection. − When an in-plane electric current flows through the heavy-metal (HM) layer with a strong spin–orbit coupling (SOC), like Pt, Ta, W, and Hf, − the spin current generated by the spin Hall effect (SHE) or the Rashba effect will switch the magnetization of the adjacent FM layer. ,− Typically, SOT-based devices exhibit lower energy consumption and higher efficiency, thus, they have also drawn great research attention through magnetic storage and other microdevices, such as racetrack domain wall memory, three-terminal magnetic tunnel junction, and magnetic random-access memory. − SOT-based research studies have various aspects. For instance, field-free switching has provided a promising method to design high-efficiency spintronic devices. ,− The investigations on the field-free SOT-induced magnetization switching have made great contributions to the applications of SOT-based devices. ,,, On the other hand, the enhancement of SOT efficiency (θ SH ) is also an essential point to be focused on. To increase the SOT efficiency, various methods have been applied, such as using HM layers with opposite sign of spin Hall angle on both sides of FM layers, rare-earth metal layers, and topological materials and modulating their spin transparency and spin current absorption. ,,− In addition, the methods mentioned above, alloying an HM layer is also an effective method to enhance the θ SH while keeping a relatively low resistance for SOT devices.…”

“…To increase the SOT efficiency, various methods have been applied, such as using HM layers with opposite sign of spin Hall angle on both sides of FM layers, rare-earth metal layers, and topological materials and modulating their spin transparency and spin current absorption. ,,− In addition, the methods mentioned above, alloying an HM layer is also an effective method to enhance the θ SH while keeping a relatively low resistance for SOT devices. Research studies have been conducted by alloying nonmagnetic impurity scatterers like Hf, Au, Cr, and Cu into metals with strong SOC to enhance the θ SH . − During the past few decades, Ru has become a popular material in spintronic industries due to its significant role on enhancing giant magnetoresistance and its great potential to reduce the critical current of the magnetization switching in a vertical spin valve. , In addition, Ru is the most traditionally used material and one of the most important materials for the synthesis of antiferromagnetic structures, which are critical for achieving field-free switching in SOT-based devices or a high-speed domain motion in a device. − Furthermore, Ru was reported to be a strong spin scatterer, which has a potential probability to enhance the extrinsic SHE as well as the θ SH . In the reported results, the studies using an alloyed HM layer are commonly concentrated on the analysis of SOT efficiency.…”

“…5,23−25 The investigations on the field-free SOTinduced magnetization switching have made great contributions to the applications of SOT-based devices. 6,17,26,38 On the other hand, the enhancement of SOT efficiency (θ SH ) is also an essential point to be focused on. To increase the SOT efficiency, various methods have been applied, such as using HM layers with opposite sign of spin Hall angle on both sides of FM layers, rare-earth metal layers, and topological materials and modulating their spin transparency and spin current absorption.…”

Experimental observation and micromagnetic understanding of the current-induced magnetization reversal process in Ta/Pt/[Co/Ni] n Co/Ta multilayers

“…In recent years, the current-induced magnetization reversal [1][2][3][4][5] and fast domain wall (DW) motion [1,[6][7][8][9] in magnetic * Author to whom any correspondence should be addressed.…”

Controllable Spin–Orbit Torque Efficiency in Pt/Co/Ru/Co/Pt Multilayers with Interlayer Exchange Couplings

“…The development of a reliable method for the local control of the magnetization is one of the critical tasks for spintronic applications. − Recently, the influence of the interlayer exchange coupling (IEC) on magnetization and spin transport has attracted a renewed interest because of the promising applications on field-free spin–orbit torque (SOT) switching, − ultrafast domain-wall (DW) motion in synthetic antiferromagnets (SAFs), , and efficient manipulation of topological magnetic textures. − Essentially, IEC is an interlayer coupling between the magnetic moments in two separated layers in a collinear fashion as described in Ruderman–Kittel–Kasuya–Yosida (RKKY) theory and/or quantum well theory, which is rooted in spin-dependent Friedel-like spatial oscillations . By changing the thickness of nonmagnetic spacer between two magnetic layers, one can tune the interaction from a preferring parallel alignment to an antiparallel alignment, which is termed ferromagnetic (FM) and antiferromagnetic (AFM) couplings, respectively.…”