Spin\u2013orbit torque driven magnetization switching in W/CoFeB/MgO-based type-Y three terminal magnetic tunnel junctions

Shinji Isogami,Atsushi Tsumita,Kosuke Hamanaka,Yugo Ishitani,Yohei Shiokawa,Eiji Komura,Tomohiro Taniguchi,Masamitsu Hayashi,Seiji Mitani,Tomoyuki Sasaki

doi:10.1038/s41598-021-95422-8

Abstract

We have studied current induced magnetization switching in W/CoFeB/MgO based three terminal magnetic tunnel junctions. The switching driven by spin—orbit torque (SOT) is evaluated in the so-called type-Y structure, in which the magnetic easy-axis of the CoFeB layer lies in the film plane and is orthogonal to the current flow. The effective spin Hall angle estimated from the bias field dependence of critical current (Ic) is ~ 0.07. The field and current dependence of the switching probability are studied. The field and DC current induced switching can be described using a model based on thermally assisted magnetization switching. In contrast, the 50 ns long pulse current dependence of the switching probability shows significant deviation from the model, even if contribution from the field-like torque is included. The deviation is particularly evident when the threshold switching current is larger. These results show that conventional thermally assisted magnetization switching model cannot be used to describe SOT induced switching using short current pulses.

Highlights

The spin–orbit torque (SOT) magnetoresistive random access memory (MRAM) is one of the emerging technologies for generation memory d evices[1, 2]
Device structure and magnetization switching by field and current
It is possible that incoherent magnetization switching that involves nucleation and subsequent motion of domain walls can cause such broadening of the switching probability

Summary

Introduction

The spin–orbit torque (SOT) magnetoresistive random access memory (MRAM) is one of the emerging technologies for generation memory d evices[1, 2]. The current passed along the HM layer generates spin current via the spin Hall effect that diffuses into the ferromagnetic free layer of the MTJ. The SOT can induce magnetization switching depending on the direction to which the current flows within the channel. As the current needed to write information (i.e. switch the magnetization) does not flow across the tunnel barrier, the three terminal SOT-MRAM is considered to possess larger endurance compared to the conventional two terminal STT-MRAM6. As field-free switching schemes for types-X and Z devices are currently being developed, the most straightforward approach to replace STT-MRAM with SOT-MRAM is to use the type-Y device. We study SOT induced magnetization switching probability of type-Y three terminal MTJ. We include the field-like torque in the model in an attempt to account for the experimental results

Methods

Results

Conclusion