Optical detection of magnetisation dynamics induced by spin-orbit torques

自旋轨道扭矩引起的磁化动力学的光学检测

• 批准号: EP/P008550/1
• 负责人: Robert Hicken
• 金额: $ 66.56万
• 依托单位: UNIVERSITY OF EXETER
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2017
• 资助国家: 英国
• 起止时间: 2017 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FP008550%2F1
• 关键词: Optical; detection; magnetisation; dynamics; induced

The modern world is completely dependent upon electronic devices that operate through the flow of charged particles called electrons i.e. electric current. However the electron also carries 'spin' angular momentum, and has an associated magnetic moment, like a tiny bar magnet. The aim of Spintronics is to use the spin of an electron to control its motion and how it interacts with magnetic materials. The most celebrated spintronic device is the 'spin-valve', a trilayer structure in which two ferromagnetic (FM) layers are separated by a non-magnetic spacer layer. The spin-valve is engineered so that the magnetic moment of one FM layer is fixed, while that of the other is free to align with an applied magnetic field, like a compass needle. As the relative orientation of the two magnetic moments varies, a large change in electrical resistance of the trilayer is observed. Since the resistance is easily measured, the spin-valve can act as a magnetic field sensor. In fact a spin-valve sensor is used to read back information in every hard disk that is sold today. When current is passed between the fixed and free FM layers an inverse effect can be observed. The flow of electrons transfers angular momentum from one FM to the other, and, by Newton's 2nd Law, exerts a spin transfer torque (STT). This torque can act upon the magnetic moment of the free layer, causing it to change its orientation. The spin-valve can also be designed to have two stables states, with different electrical resistance, that can be used to store digital information. Arrays of such devices are used in magnetic random access memory (MRAM). Alternatively, in a spin transfer oscillator (STO), the free layer magnetization oscillates at microwave frequency when DC current is applied. Since the resistance also oscillates, microwave voltage oscillations are generated. The STO is unusual in that its frequency can be tuned through multiple octaves by varying the DC current. Multiple STOs can be defined at chip level, as circuit components, or in arrays for increased power output.In recent years it has been realized and demonstrated that the spin-orbit interaction, a relativistic effect, may also be used to manipulate the electron spin. The spin can in turn be used to generate a STT, which has been termed spin-orbit torque (SOT) in light of its origin. SOTs are generated by the spin Hall effect (SHE) and the Rashba effect, but the separation of these torques from each other, and from the torque generated by the flow of charge (Oersted torque), is still being debated. The optimization of SOT for use in MRAM has attracted enormous interest because it removes the need to pass large electric currents through fragile insulating layers that conduct electricity by quantum mechanical tunneling.In this project we will use time resolved scanning Kerr microscopy (TRSKM) to explore, understand and optimize SOTs in device structures of the highest quality supplied by HGST, Brown University and the University of Gothenburg, all of whom are leaders in their respective fields. Crucially we will modify our TRSKM so that a magnetic field can be applied with any orientation in 3 dimensional space, while high frequency electrical probes are connected to the device, and a focused optical probe is used to determine the instantaneous orientation of the magnetization vector. This internationally unique instrument will allow us to determine the SOTs from the static and dynamic response of the magnetization, rather than the electrical resistance, as different electrical stimuli are applied. Furthermore the sub-micron spatial resolution of TRSKM will allow us to separate different torques through their spatial variation, and understand how SOTs interact with dynamic magnetic modes in a confined geometry. Finally, we will use this same instrument to understand how SOTs induce magnetic precession in STOs and switching in candidate MRAM devices.

现代世界完全依赖于电子设备，这些设备通过称为电子的带电粒子流（即电流）运行。然而，电子也携带“自旋”角动量，并具有相关的磁矩，就像一个微小的条形磁铁。自旋电子学的目的是利用电子的自旋来控制它的运动以及它如何与磁性材料相互作用。最著名的自旋电子器件是“自旋阀”，这是一种三层结构，其中两个铁磁（FM）层被非磁性间隔层隔开。自旋阀的设计使得一个FM层的磁矩是固定的，而另一个层的磁矩可以自由地与施加的磁场对齐，就像指南针一样。随着两个磁矩的相对取向的变化，观察到三层膜的电阻发生了很大的变化。由于电阻很容易测量，自旋阀可以用作磁场传感器。事实上，自旋阀传感器被用来读回今天出售的每一个硬盘中的信息。当电流在固定和自由FM层之间通过时，可以观察到相反的效果。电子流将角动量从一个FM转移到另一个FM，并且根据牛顿第二定律，施加自旋转移力矩（STT）。该扭矩可以作用于自由层的磁矩，使其改变其取向。自旋阀也可以设计成具有两个稳定状态，具有不同的电阻，可以用来存储数字信息。这种器件的阵列用于磁性随机存取存储器（MRAM）中。或者，在自旋转移振荡器（STO）中，当施加DC电流时，自由层磁化以微波频率振荡。由于电阻也振荡，所以产生微波电压振荡。STO的不寻常之处在于它的频率可以通过改变直流电流来调谐多个倍频程。多个STO可以被定义在芯片级，作为电路元件，或在阵列中以增加功率输出。近年来，人们已经认识到并证明，自旋轨道相互作用，一种相对论效应，也可以用来操纵电子自旋。自旋又可以用来产生一个STT，根据它的起源，它被称为自旋轨道力矩（SOT）。SOT由自旋霍尔效应（SHE）和Rashba效应产生，但这些扭矩彼此分离，以及与电荷流产生的扭矩（奥斯特扭矩）分离，仍在争论中。在MRAM中使用的SOT的优化吸引了巨大的兴趣，因为它消除了通过量子力学隧道导电的脆弱绝缘层通过大电流的需要。在这个项目中，我们将使用时间分辨扫描克尔显微镜（TRSKM）来探索，理解和优化由HGST，布朗大学和哥德堡大学提供的最高质量的器件结构中的SOT，他们都是各自领域的领导者。至关重要的是，我们将修改我们的TRSKM，以便可以在三维空间中以任何方向施加磁场，同时将高频电探针连接到设备，并使用聚焦光学探针来确定磁化矢量的瞬时方向。这种国际上独一无二的仪器将使我们能够根据磁化的静态和动态响应来确定SOT，而不是电阻，因为施加了不同的电刺激。此外，TRSKM的亚微米空间分辨率将允许我们通过它们的空间变化来分离不同的扭矩，并了解SOT如何在受限的几何形状中与动态磁模式相互作用。最后，我们将使用相同的仪器来了解SOT如何在STO中诱导磁旋进并在候选MRAM器件中切换。

项目成果

Time-domain imaging of curling modes in a confined magnetic vortex and a micromagnetic study exploring the role of spiral spin waves emitted by the core

• DOI: 10.1103/physrevb.103.064408
• 发表时间: 2020-07
• 期刊: arXiv: Mesoscale and Nanoscale Physics
• 作者: D. Osuna Ruiz;P. Keatley;J. Childress;J. Katine;R. Hicken;A. Hibbins;F. Ogrin

Current-induced picosecond magnetization dynamics in a Ta/CoFeB/MgO hall bar

Ta/CoFeB/MgO 霍尔棒中的电流感应皮秒磁化动力学

• DOI: 10.1088/1361-6463/ab2693
• 发表时间: 2019
• 期刊: Applied Physics
• 作者: Spicer T

Optically detected spin-orbit torque ferromagnetic resonance in an in-plane magnetized ellipse

平面内磁化椭圆中光学检测的自旋轨道扭矩铁磁共振

• DOI: 10.1063/5.0035582
• 发表时间: 2021
• 期刊: Applied Physics Letters
• 影响因子: 4
• 作者: Keatley P

Time-resolved imaging of magnetization dynamics in double nanocontact spin torque vortex oscillator devices

• DOI: 10.1103/physrevb.100.134439
• 发表时间: 2019-10
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: E. Burgos-Parra;P. Keatley;S. Sani;P. Durrenfeld;J. Åkerman;R. Hicken

Time resolved imaging of the non-linear bullet mode within an injection-locked nano-contact spin Hall nano-oscillator

• DOI: 10.1063/1.5047148
• 发表时间: 2018-05
• 期刊: Applied Physics Letters
• 影响因子: 4
• 作者: T. M. Spicer;P. Keatley;M. Dvornik;T. Loughran;A. Awad;P. Dürrenfeld;A. Houshang;M. Ranjbar;J. Åkerman;V. Kruglyak;R. Hicken