Non-local spin transport across electronic phase transitions

纳米级磁学和自旋电子学（操纵电子的自旋）的成功已经使材料的设计磁性成为可能。然而，这些成就更加强调对电子自旋输运的精确控制。这一点在硬盘驱动器读磁头的情况下最为明显，读磁头尺寸的持续减小严重限制了隧道磁阻传感器的未来使用，这是ICT行业面临的主要挑战。低阻抗的替代品现在正在积极寻求，全金属器件回到了最前沿的兴趣。值得注意的是，尽管像读磁头这样的自旋电子器件无处不在，但我们对纳米尺度金属系统中自旋输运的理解仍然存在明显的差距。即使在磁阻器件中使用的（相对）简单的铁磁性和非磁性材料中，最近的结果也对我们在这一水平上的理解提出了质疑。这给它们的未来使用带来了许多重大挑战。除了这些材料之外，我们所知的就更少了，总的来说，精确电子相和自旋输运之间更广泛的相互作用才刚刚开始被探索。这种限制对当前技术的影响是显而易见的，绝大多数自旋电子设备仅限于考虑远程铁磁材料的操作，例如在存储应用中。事实上，除了铁磁开关之外，用自旋控制状态的可能性，可能会给自旋电子设备带来全新的功能，可能会带来变革性的新技术——这是一个令人兴奋的前景。本提案的目的是探索使用纯自旋电流介导相变。我们将首先探索纯自旋输运，使用一种称为“非局部自旋阀”的设备作为研究平台，将复杂的磁性材料结合起来。最初，这将涉及定制自旋通道特性，以系统地揭示限制自旋输运的特定缺陷的作用——这是增强金属器件中自旋信号的关键结果。然后，我们将进一步了解电子相和自旋扩散之间的相互作用，试图探索一系列基本相变的自旋输运，包括自旋玻璃冻结、金属到绝缘和铁到反铁磁。通过这样做，将揭示有关自旋电流与相位相互作用的大量新信息。通过一系列自旋产生技术，我们将研究吸收自旋电流的扭矩在稳定相位、提高临界温度、移动相位边界和诱导这些转变的临界波动中的作用。通过使用NLSV进行这些研究，我们将能够在一个新颖但技术相关的环境中探索这种影响。

The successes of nanoscale magnetism and spintronics (where the spin of the electron is manipulated) have been enabling for materials-by-design magnetism. However, these accomplishments have placed ever more emphasis on precisely controlling the transportation of electron spin. This is nowhere more critically seen than in the case of hard disk drive read heads, where continued reduction in read head size places serious limits to the future use of tunnel magneto-resistance sensors - a major challenge for the ICT industry. Low impedance alternatives are now actively sought, with all-metallic devices returning to the forefront of interest. Remarkably, despite the ubiquity of spintronic devices like read heads, there remain stark gaps in our understanding of spin transport in metallic systems at the nanoscale. Even in the (relatively) simple ferromagnetic and non-magnetic materials used in magnetoresistive devices, recent results have called into question our understanding at this level. This imposes a number of substantial challenges for their future use. Moving beyond these materials even less is known and, in general, the wider interplay between precise electronic phase and spin transport is only beginning to be probed. The impact of such limitations to current technology is readily seen, with the vast majority of spintronic devices limited to considering only the manipulation of long-range ferromagnetic materials, e.g. in storage applications. Indeed, the possibility of controlling state with spin, beyond ferromagnetic switching, could bring entirely new functionality to spintronic devices, potentially leading to transformative new technologies -- an exciting prospect.The aim of this proposal is to explore mediating phase transitions using pure spin currents. We will first explore pure spin transport, using a device known as a 'non-local spin valve' as a research platform to incorporate complex magnetic materials. Initially this will involve tailoring spin channel properties to systematically bring to light the role of specific defects in limiting spin transport -- crucial results for enhancing spin signals in metallic devices. We will then move to understand the interplay between electronic phase and spin diffusion, attempting to probe spin transport across a host of fundamental phase transitions, including spin glass freezing, metallic to insulating and ferro- to antiferro-magnetic. By doing so, a wealth of new information on the interaction of spin currents with phase will be revealed. Through a number of spin generation techniques, we will examine the role of the torques from absorbed spin currents in stabilising phases, enhancing critical temperatures, moving phase boundaries and inducing critical fluctuations across a host of these transitions. By using the NLSV for these studies, we will be able to explore such effects in a novel but technologically relevant environment.