ChinesePhysicsL的个人博客分享 http://blog.sciencenet.cn/u/ChinesePhysicsL

博文

同行点评 | Orbit-Transfer Torque Switching

已有 250 次阅读 2022-7-17 20:53 |系统分类:论文交流

1.gif

Received 2 June 2022; published online 18 June 2022


Viewpoint

Orbit-Transfer Torque Switching

Yeliang Wang (王业亮)

Chin. Phys. Lett. 2022, 39 (7): 070101

http://cpl.iphy.ac.cn/article/10.1088/0256-307X/39/7/070101

应编辑部邀请,北京理工大学的王业亮教授撰写了这篇论文,深度点评了发表在CPL的一篇Express Letter。


EXPRESS LETTER

Orbit-Transfer Torque Driven Field-Free Switching of Perpendicular Magnetization

Xing-Guo Ye (叶兴国), Peng-Fei Zhu (朱鹏飞), Wen-Zheng Xu (徐文正), Nianze Shang (尚念泽), Kaihui Liu (刘开辉), and Zhi-Min Liao (廖志敏) Chin. Phys. Lett. 2022, 39 (3): 037303

http://cpl.iphy.ac.cn/article/10.1088/0256-307X/39/3/037303


文章亮点

首次提出并实现了轨道转移矩(orbit-transfer torque, OTT)效应,是继自旋转移矩(spin-transfer torque, STT)、自旋轨道矩(spin-orbit torque, SOT)之后一种实现无需外磁场辅助且高效的垂直磁化翻转的全新策略。


640.png

轨道转移矩的物理图像及输运测量结果。左上:在铁磁/非磁异质结中,电流驱动的轨道磁矩极化(绿色箭头)产生轨道转移矩TOTT。轨道转移矩作用于铁磁层的磁矩M,实现无需外磁场的垂直磁化翻转。右上:在具有非零贝利曲率偶极矩D的二维体系中,存在电流诱导的轨道磁矩极化。左下:WTe2/Fe3GeTe2异质结中二阶非线性霍尔效应的角度依赖测量。中下:在WTe2/Fe3GeTe2异质结施加沿着WTe2a轴的脉冲电流,通过轨道转移矩实现了确定性的垂直磁化翻转。右下:在异质结中施加沿着WTe2b轴的脉冲电流,由于该方向没有非零的贝利曲率偶极矩,施加电流不能产生轨道转移矩,从而无法实现确定性的磁化翻转。


磁性随机存储器(MRAM)是一种高速度、低功耗的非易失性存储器件。要实现MRAM,关键在于实现电流驱动下铁磁层的磁化翻转。目前主要通过奥斯特场、自旋转移矩和自旋轨道矩三种方式来实现磁化翻转。利用电流诱导的奥斯特场实现磁化翻转的器件结构复杂,能耗较高。自旋转移矩则面临读写路径不分离,从而耐用性较差的问题。而基于拓扑表面态、Rashba效应或者自旋霍尔效应的自旋轨道矩则通常面临着与垂直磁化翻转不兼容的问题——而后者正是MRAM器件小型化的关键。要利用自旋轨道矩实现垂直磁化翻转,通常需要特殊的结构设计或者外磁场的辅助。


最近,北京大学廖志敏课题组基于固体中布洛赫电子的轨道磁矩,提出并成功展示了利用轨道转移矩实现无需外磁场的垂直磁化翻转。不同于自旋,二维材料中电子的轨道磁矩由于维度的限制而自然地沿着面外方向。他们构筑了WTe2/Fe3GeTe2异质结,薄层WTe2作为非磁层、少层Fe3GeTe2作为具有垂直磁化的铁磁层;利用WTe2中沿着a轴方向的贝利曲率偶极矩,施加电流诱导实现了轨道磁矩极化,轨道转移矩作用于Fe3GeTe2铁磁层,实现了无外磁场下的垂直磁化翻转。


该工作提出的轨道转移矩,作为一种无需外磁场辅助、实现垂直磁化翻转的新策略,将为低功耗、高可靠性、高耐受性MRAM的高密度集成与大规模应用提供一种可行途径。


Orbit-Transfer Torque Switching

In the post-Moore era, memory devices with smaller sizes, lower energy consumption, and higher reliability are desired. As a classic type of non-volatile memory, magnetic random-access memory (MRAM) is outstanding, since it keeps data storage by magnetic states (electron spin) instead of electron charges. Specifically, in MRAM, the data is stored in the magnetic tunnel junction unit, and the logical 0 and 1 are determined by the parallel and antiparallel magnetic states of the two ferromagnetic layers, respectively.


In the past, spin-torque, including spin-transfer torque (STT) and spin-orbit torque (SOT), is exploited to realize the switching of magnetic states. STT-MRAM is implemented in a two-terminal device,[1,2] where the “writing” current and “reading” current are applied along the same channel. The “writing” current, which is exploited to realize magnetization switching, is usually large, leading to the severe heating problem and poor endurance.


Different from two-terminal STT-MRAM, SOT-MRAM has a three-terminal configuration, which is favorable to achieve magnetization switching by polarized spin current with spin-torque, based on spin Hall effect or spin Rashba–Edelstein effect.[3,4] Unfortunately, conventional SOT-MRAM is incompatible with perpendicular magnetization switching that is necessary for device scaling down and high integration density. To realize perpendicular magnetization switching in SOT, either an external in-plane magnetic field or structure asymmetry of the device is needed.


A recent work[5] published in Chinese Physics Letters reports a new route to realize perpendicular magnetization switching in the absence of an external magnetic field, that is, so-called orbit-transfer torque (OTT). The OTT exploits the orbital magnetic moment instead of the spin of the Bloch electrons. The key point is that the orbital magnetic moment generates the torque effect. Intriguingly, in some two-dimensional materials, the orbital magnetic moment is forced to be out of plane due to dimension constraint, facilitating the field-free perpendicular magnetization switching of the adjacent ferromagnetism.


In that work, Ye and his colleagues proposed the concept of OTT and successfully demonstrated the OTT-driven perpendicular magnetization switching in WTe2/Fe3GeTe2 heterostructure devices.[5] The authors show that the magnetization of Fe3GeTe2 is switched by applying an electrical current in the adjacent WTe2 layer. The WTe2 layer holds a nonzero Berry curvature dipole, which is defined as the dipole moment of Berry curvature in momentum space.[6] Thus the polarization of orbital magnetism in such heterostructures is generated by an electric current rather than an external magnetic field [Fig. 1].


1.png

Fig. 1. Illustration of orbit-transfer torque switching. In a heterostructure consisting of ferromagnetic Fe3GeTe2 and non-magnetic WTe2, the nonzero Berry curvature dipole at the interface results in the polarization of orbital magnetic moment, thus yielding magnetization switching in Fe3GeTe2. Such upward and downward magnetization states can be reversibly switched by injecting opposite directions of current.


The discovery of OTT is significant for both fundamental scientific research and technology application in future. Firstly, the OTT is a new mechanism for magnetization reversal after STT and SOT. Secondly, the OTT surpasses the previous STT and SOT for field-free perpendicular magnetization switching and has more realistic application prospects for the upcoming OTT-MRAM. Moreover, the OTT exploits the current-induced polarized orbital magnetic moment of Bloch electrons, extending the concept from spintronics to orbitronics and even their hybrid. OTT also enables three-terminal MRAM devices, and thus combines the advantages of high speed, high density, and low energy consumption.


References

[1] Slonczewski J C 1996 J. Magn. Magn. Mater. 159 L1

[2] Sankey J C, Cui Y T, Sun J Z, Slonczewski J C, Buhrman R A, and Ralph D C 2008 Nat. Phys. 4 67

[3] Liu L, Pai C F, Li Y, Tseng H W, Ralph D C, and Buhrman R A 2012 Science 336 555

[4] Liu L, Lee O J, Gudmundsen T J, Ralph D C, and Buhrman R A 2012 Phys. Rev. Lett. 109 096602

[5] Ye X G, Zhu P F, Xu W Z, Shang N Z, Liu K H, and Liao Z M 2022 Chin. Phys. Lett. 39 037303 

[6] Sodemann I and Fu L 2015 Phys. Rev. Lett. 115 216806


研究快讯集锦

变分角转移矩阵重正化群方法及其在经典统计模型中的应用

在单比特上基于量子态判别的互文性实验验证

巨行星内部可能存在的氦-二氧化硅化合物

范德瓦尔斯超导材料中准二维超导电性和可调控近藤晶格的共存

QCD强耦合常数在微扰及非微扰能区跑动行为的新分析

始于生成网络的马尔可夫链蒙卡

压力诱导具有超高能量密度的含氖聚合氮化物

FeSe超导体的反常能带劈裂和强各向异性超导能隙随掺硫的奇异演变

锁相热扩散趋肤效应

用于拓扑量子器件的纯相超细InAs–Al纳米线原位分子束外延

α-CsPbI3的缺陷容忍性:高温相材料中点缺陷性质的计算方法

Valence Quark Ratio in the Proton

高混合熵提升非晶合金的能量状态

在可调耦合超导量子比特中实现全微波脉冲的CZ门

BaO/SrTiO3界面的电输运性质研究

高通量第一性原理计算探索潜在的笼目材料

4.png

点此浏览所有Express Letters

CPL Express Letters栏目简介

为了保证重要研究成果的首发权和显示度,CPL于2012年6月开设了Express Letters栏目。此栏目发表速度快,学术质量高。截至2020年底,平均每篇被引用约20次,已经在国内物理学界建立起良好口碑与声望,来稿数量不断增加。

3.jpg

阅读原文




https://blog.sciencenet.cn/blog-3426263-1347660.html

上一篇:研究快讯 | 氦离子注入制备的钇钡铜氧高温超导约瑟夫森结
下一篇:研究快讯 | 伊辛模型的几何上临界维度
收藏 IP: 141.52.249.*| 热度|

0

该博文允许注册用户评论 请点击登录 评论 (0 个评论)

数据加载中...

Archiver|手机版|科学网 ( 京ICP备07017567号-12 )

GMT+8, 2022-9-28 04:35

Powered by ScienceNet.cn

Copyright © 2007- 中国科学报社

返回顶部