Magneto-transport in mutilayers and nanostructures with strong spin-orbit coupling

许多现代数据存储和通信设备都是由磁性材料制成的。例如，现代计算机硬盘驱动器和磁性随机存取存储器（MRAM）包含大小为几十纳米的磁性元件。在这种装置中，磁性元件的磁化方向用于存储信息。目前用于控制磁化方向的方法涉及使用电流来局部产生磁场或使用称为自旋转移力矩的效应来切换磁化。由于需要将产生磁场的部件与其他磁性设备集成，这些技术具有诸如能量耗散和对磁分离的限制的缺点。这些问题的潜在解决方案正在由诺丁汉大学的实验凝聚态研究组研究，将是创造一种通过施加电场或机械应变来控制磁状态的设备。金属合金和多层膜具有很强的相对论效应，称为自旋-轨道耦合。我的建议旨在从理论上研究这些材料和器件的特性。与诺丁汉实验组的直接合作将促进理论预测的适用性，激发新的实验和新的理论研究，并为纳米结构的设计提供指导。我将采用已建立的理论模型和技术（如紧束缚模型和Landauer Buttiker形式主义）来计算器件的磁和电特性。我也会用更先进的技术（如非平衡绿色函数技术）来计算与信息处理设备的速度相关的超快时间尺度上的设备的属性。我将通过将微观计算的结果插入宏观模拟并研究机械，纳米机电系统（NEMS）中的电和磁自由度，其是诸如纳米级振荡梁或杠杆的装置，具有作为高灵敏度质量传感器和致动器的潜在应用。这类器件对于量子和经典物理学之间的重叠的更基础的研究也是有趣的。这一提议的动机是学术和商业上的需求，以发展对由具有强自旋轨道耦合的金属材料和多层膜制成的纳米级器件的更广泛的理解，并在此类器件中寻找新的功能。这项工作的结果将引领新的非易失性，电操纵存储器设备的方式。

Many modern data storage and communications devices are made on a very small scale from magnetic materials. For example, modern computer hard drives and magnetic random access memory (MRAM) contain magnetic elements that are a few tens of nanometres in size. In such devices the direction of the magnetisation of the magnetic elements is used to store information. The methods currently used to control the direction of magnetisation involve using electrical current to generate a magnetic field locally or to switch the magnetisation using an effect called spin transfer torque . These techniques have disadvantages such as energy dissipation and limits on miniaturisation, due to the need to integrate the components which generate the field with other magnetic devices.A potential solution to these problems, which is being studied by the Experimental Condensed Matter Research Group at the University of Nottingham, would be to create devices in which the magnetic state is controlled by applying an electric field or a mechanical strain. Metallic alloys and multilayers which possess a strong relativistic effect called spin-orbit coupling are used. My proposal aims to study the properties of such materials and devices on a theoretical level. The direct collaboration with the experimental group at Nottingham will promote the applicability of the theoretical predictions, inspire new experiments and new theoretical investigations, and provide guidance in the design of the nanostructures. I will employ established theoretical models and techniques (such as the tight binding model and the Landauer Buttiker formalism) to calculate the magnetic and electrical properties of the devices. I will also use more advanced techniques (such as the non-equilibrium Green's function technique) to calculate the properties of the devices on ultra-fast timescales relevant to the speeds of information processing devices.I will complement these studies by inserting the results of the microscopic calculations into a macroscopic simulation and investigating the coupling of mechanical, electrical and magnetic degrees of freedom in nano-electro-mechanical systems (NEMS), which are devices such as nanoscale oscillating beams or cantilevers with potential applications as highly sensitive mass sensors and actuators. Such devices are also interesting for more fundamental studies of the overlap between quantum and classical physics.This proposal is motivated by both the academic and the commercial demand for developing a broader understanding of nanoscale devices made from metallic materials and multilayers possessing strong spin-orbit coupling and the search for new functionalities in such devices. The results of this work will lead the way to new non-volatile, electrically-manipulated memory devices.