Electric-field control of field-free spin-orbit torque switching via laterally modulated Rashba effect in Pt/Co/AlOx structures

Min-Gu Kang,Kab-Jin Kim,Taehwan Kim,Jong-Ryul Jeong,Jung Hyun Oh,Jong Min Yuk,Taekhyeon Lee,Jimin Jeong,Jongsun Park,Jae Yeol Park,Jong-Guk Choi,Hyeon-Jong Park,Byong-Guk Park,Kyoung-Whan Kim,Kyung-Jin Lee,Duc Duong Viet

doi:10.1038/s41467-021-27459-2

Abstract

Spin-orbit coupling effect in structures with broken inversion symmetry, known as the Rashba effect, facilitates spin-orbit torques (SOTs) in heavy metal/ferromagnet/oxide structures, along with the spin Hall effect. Electric-field control of the Rashba effect is established for semiconductor interfaces, but it is challenging in structures involving metals owing to the screening effect. Here, we report that the Rashba effect in Pt/Co/AlOx structures is laterally modulated by electric voltages, generating out-of-plane SOTs. This enables field-free switching of the perpendicular magnetization and electrical control of the switching polarity. Changing the gate oxide reverses the sign of out-of-plane SOT while maintaining the same sign of voltage-controlled magnetic anisotropy, which confirms the Rashba effect at the Co/oxide interface is a key ingredient of the electric-field modulation. The electrical control of SOT switching polarity in a reversible and non-volatile manner can be utilized for programmable logic operations in spintronic logic-in-memory devices.

Highlights

Spin-orbit coupling effect in structures with broken inversion symmetry, known as the Rashba effect, facilitates spin-orbit torques (SOTs) in heavy metal/ferromagnet/oxide structures, along with the spin Hall effect
We show that the z-SOT and associated switching polarity are controllable by gate voltage in a reversible and nonvolatile manner, offering programmable logic operations in spintronic login-in-memory devices as demonstrated below
To demonstrate the z-SOT generated by asymmetric gate voltages, we fabricate Pt (5 nm)/Co (1.4 nm)/AlOx (2 nm) Hall-bar devices, in which two side gates consisting of a gate oxide of TiO2 (40 nm) and a gate electrode of Ru (50 nm) are integrated (Fig. 1b and Methods)

Summary

Introduction

Spin-orbit coupling effect in structures with broken inversion symmetry, known as the Rashba effect, facilitates spin-orbit torques (SOTs) in heavy metal/ferromagnet/oxide structures, along with the spin Hall effect. Changing the gate oxide reverses the sign of out-of-plane SOT while maintaining the same sign of voltage-controlled magnetic anisotropy, which confirms the Rashba effect at the Co/ oxide interface is a key ingredient of the electric-field modulation. We report that the lateral modulation of Rashba effect in Pt/Co/AlOx structures by using two side gates generates out-of-plane SOT, allowing electrical control of field-free switching of perpendicular magnetization. It is of crucial importance to identify the microscopic origin of the electric-fieldinduced lateral symmetry breaking for further improvement of device performance To this end, we show that the z-SOT depends on gate oxide materials; the direction of the z-SOT in the identical Pt/Co/AlOx structures is reversed by changing the gate oxide from TiO2 to ZrO2. Co/AlOx interface, which is further supported by the measurements of the gate-voltage dependence of field-like SOTs

Methods

Results

Conclusion