Spin@RT: Room Temperature Spintronics

自旋电子学的目的是控制电子自旋，以便在新一代电子设备中提供新的功能。在追求这一目标的过程中，有许多令人兴奋的前沿基础物理学，这是我们将集中努力的地方。第一代自旋电子学已经伴随我们好几年了，其中硬盘读头等设备是金属基设备的常见例子。在自旋电子学中使用半导体方面也有相当多的研究工作，但由于案例中明确的原因，我们将集中于金属和氧化物自旋电子学的研究。自旋电子学已经达到了一个阶段，在这个阶段，进一步的重大进展需要基于不同物理性质的新一代设备。我们的建议有四个主题。首先，我们提出利用电子波函数的相干性在电荷和自旋在外延磁性纳米结构的整个厚度上的输运过程中可能被保留的新想法。据预测，相干输运将提高磁电阻（MR）一个数量级以上。磁随机存取存储器（MRAM）等自旋电子器件的磁随机存取存储器的这种改进将产生巨大的影响。在第二个主题中，我们打算以一种全新的方式使用基于设施的x射线源的分辨率，特别是观察自旋极化电流注入导致贵金属自旋极化的微小但重要的变化。第一次对自旋积累的直接测量将提供自旋电流转矩的详细信息，这是目前缺失的，但迫切需要在第三个主题中描述的研究。这种测量将依赖于我们在大面积纳米器件制造、同步辐射和微尺度波导高频测量方面的专业知识。在第三个主题中，我们将使用迄今尚未开发的x射线，中子和时间分辨光学技术来研究纳米柱阵列电流诱导磁态的时空相干性，以区分自旋传递扭矩的分析模型，并了解最近报道的丰富动态行为。实验和理论之间的密切相互作用将使我们不仅能够理解，而且能够通过材料和实验几何的选择来操纵动态行为。最后，在第四个主题中，我们将使用纳米加工技术从磁阻材料中创建新的纳米线结构，并使用强大的磁性表征工具集合来观察电流诱导的畴壁运动。这将使我们能够解决一些关键但有争议的问题，如诱导壁面运动所需的最小电流密度，壁面速度的内在限制，以及畴壁结构的影响。

The aim of spintronics is to control the electron spin so that it can be used to provide new functionality in a new generation of electronic devices. Within the pursuit of this aim there is a great deal of exciting cutting-edge fundamental physics and this is where our efforts will be concentrated. The first generation of spintronics has been with us for several years where devices such as read-heads for hard discs are a commonplace example of a metal-based device. There is also considerable research effort into the use of semiconductors in spintronics, but for reasons made clear in the case, we shall concentrate on metal and oxide spintronic research. Spintronics has reached a stage where further significant progress requires a new generation of devices based on a qualitatively different physics. Our proposal has four major themes. In the first we propose to exploit the new idea that the coherence of electron wave functions may be preserved during the transport of charge and spin across the entire thickness of an epitaxial magnetic nanostructure. It has been predicted that coherent transport will improve the magnetoresistance (MR) by more than an order of magnitude. The impact of such an improvement in MR alone on spintronic devices such as magnetic random access memory (MRAM) will be immense. In the second theme we intend to use the resolution of facility-based x-ray sources in an entirely new way, specifically, to observe the small but significant changes in the spin polarisation of a noble metal that result from injection of a spin-polarised current. This first direct measurement of spin accumulation will provide detailed information on spin-current torque which is currently missing but urgently required for the research described in the third theme. Such measurements will rely on our expertise in large area nano-device fabrication, the use of synchrotron radiation and high frequency measurements in micro-scale waveguides. In the third theme we will study the temporal and spatial coherence of the current-induced magnetic state of nano-pillar arrays using hitherto unexploited x-ray, neutron and time-resolved optical techniques to distinguish between analytical models for spin-transfer torque, and to understand the rich dynamic behaviour that has recently been reported. Close interplay between experiment and theory will allow us not only to understand but also to manipulate the dynamic behaviour through the choice of materials and experimental geometry. Finally, in the fourth theme, we will use nanofabrication to create novel nanao-wire structures from magnetoresistive materials and employ a powerful collection of magnetic characterisation tools to observe the current-induced motion of domain walls. This will allow us to resolve a number of critical but controversial issues such as the minimum current density required to induce wall motion, the intrinsic limit upon wall velocity, and the influence of domain wall structure.