Voltage-induced magnetization dynamics in CoFeB/MgO/CoFeB magnetic tunnel junctions

Katsuya Miura,Yoshichika Otani,Masahiko Ichimura,Bivas Rana,Susumu Ogawa,Shin Yabuuchi,Yasuhiro Fukuma,Masaki Yamada,Hiromasa Takahashi

doi:10.1038/srep42511

Abstract

Recent progress in magnetic tunnel junctions (MTJs) with a perpendicular easy axis consisting of CoFeB and MgO stacking structures has shown that magnetization dynamics are induced due to voltage-controlled magnetic anisotropy (VCMA), which will potentially lead to future low-power-consumption information technology. For manipulating magnetizations in MTJs by applying voltage, it is necessary to understand the coupled magnetization motion of two magnetic (recording and reference) layers. In this report, we focus on the magnetization motion of two magnetic layers in MTJs consisting of top layers with an in-plane easy axis and bottom layers with a perpendicular easy axis, both having perpendicular magnetic anisotropy. According to rectified voltage (Vrec) measurements, the amplitude of the magnetization motion depends on the initial angles of the magnetizations with respect to the VCMA direction. Our numerical simulations involving the micromagnetic method based on the Landau-Lifshitz-Gilbert equation of motion indicate that the magnetization motion in both layers is induced by a combination of VCMA and transferred angular momentum, even though the magnetic easy axes of the two layers are different. Our study will lead to the development of voltage-controlled MTJs having perpendicular magnetic anisotropy by controlling the initial angle between magnetizations and VCMA directions.

Highlights

Electron-spin-related phenomena have been attracting much attention because of their potential for enabling innovation in information processing technologies such as magnetic random access memory (MRAM)[1,2,3] and nonvolatile logic chips
Both ferromagnetic layers in our magnetic tunnel junctions (MTJs) have interfacial perpendicular magnetic anisotropy (PMA) because they have an interface with the MgO layer
We have investigated the magnetization motion in the two magnetic layers in MTJs under applied radio frequency (RF) voltage by using both experimental measurements and micromagnetic simulations by taking into account voltage-controlled magnetic anisotropy (VCMA)

Summary

Introduction

Electron-spin-related phenomena have been attracting much attention because of their potential for enabling innovation in information processing technologies such as magnetic random access memory (MRAM)[1,2,3] and nonvolatile logic chips. In addition to STT magnetization switching, the discovery of perpendicular magnetic anisotropy (PMA) at the interface between CoFeB and MgO8,9, which are widely used in magnetic tunnel junctions (MTJs)[8,9,10,11,12] due to their giant tunnel magnetoresistance (TMR)[13], is substantial progress in developing practical MRAM. To further reduce power consumption, many different trials for manipulating magnetic properties by voltage have been conducted, including voltage control of magnetostriction in multilayered stacks with piezoelectric materials[14,15], Currie temperature in ferromagnetic semiconductors[16,17], magnetoelectric effect in multiferroic materials[18] or ferroelectric/ferromagnetic heterostructures[19], and magnetic anisotropy[20,21]. The power consumption in MRAM can be significantly reduced if magnetizations in MTJs are fully controlled by applying voltage.

Methods

Results

Conclusion