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.

现代世界完全取决于通过称为电子（电流）的带电粒子流动的电子设备。但是，电子还具有“自旋”角动量，并且具有相关的磁矩，例如微型棒磁体。 Spirtronics的目的是使用电子的自旋来控制其运动及其与磁性材料的相互作用。最著名的自旋装置是“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。自旋阀经过设计，使一个FM层的磁矩是固定的，而另一个FM层的磁矩可以自由与施加的磁场保持一致，例如指南针。随着两个磁矩的相对方向变化，观察到三层电阻的大幅变化。由于电阻很容易测量，因此自旋阀可以充当磁场传感器。实际上，使用自旋阀传感器来读取今天出售的每个硬盘中的回报信息。当固定和游离FM层之间传递电流时，可以观察到反效应。电子的流量将角动量从一个FM传递到另一个FM，并且通过牛顿的第二定律，发出了自旋转移扭矩（STT）。该扭矩可以作用于自由层的磁矩，从而改变其方向。旋转阀还可以设计为具有两个具有不同电阻的马s状态，可用于存储数字信息。此类设备的阵列用于磁随机访问存储器（MRAM）。另外，在旋转转移振荡器（STO）中，当应用直流电流时，自由层磁化值在微波频率下振荡。由于电阻也振荡，因此产生微波电压振荡。 STO是不寻常的，因为它的频率可以通过改变直流电流来通过多个八度进行调节。可以在芯片水平上定义多个STOS，作为电路组件或在阵列中以增加功率输出。近年来，它已经实现并证明了自旋轨道相互作用（一种相对论效应）也可以用于操纵电子自旋。旋转可以用于生成一个STT，该STT被称为旋转轨道扭矩（SOT），鉴于其起源。 SOT是由旋转厅效应（SHE）和RashBA效应产生的，但是这些扭矩之间的分离以及从电荷流（Oersted Torque）产生的扭矩（Oersted Torque）仍在争论中。在MRAM中使用SOT的优化引起了极大的兴趣，因为它需要通过量子机械隧道传递大型电流，这些电流通过脆弱的绝缘层进行电力层。在这个项目中，我们将使用时间分析的KERR显微镜（TRSKM）来探索，理解和优化最高质量的Sots and Hergs and Hg St.各自领域的领导人。至关重要的是，我们将修改TRSKM，以便可以在3维空间中使用任何方向应用磁场，而高频电气探针则连接到设备，并使用聚焦的光学探测来确定磁化载体的瞬时方向。这种国际独特的仪器将使我们能够从磁化强度的静态和动态响应（而不是电阻）中确定SOT，因为应用了不同的电刺激。此外，TRSKM的亚微米空间分辨率将使我们能够通过它们的空间变化分离不同的扭矩，并了解SOTS如何在牢固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如何诱导STOS中的磁性动力并在候选MRAM设备中转换。

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