Thermal gradient engineering for spin injection and transport in metallic nanomagnetic switches and sensors

目前能够实现快速信息处理和海量数据存储的电子和磁性设备部分使用尺寸接近100纳米的金属结构形成。通常这些装置的功能是由于施加的电子流，而这种电荷流产生热量。在许多情况下，这种热量限制了这些微型设备的性能，并阻碍了技术的进步。该项目旨在通过研究一种被称为非局部自旋阀的特定纳米级金属磁性装置的热效应，探索同时避免或利用这种加热的方法。人们已经知道，这些装置可以在金属纳米线中产生角动量流或自旋流，而没有相关的电荷流。然而，它们的操作通常需要在器件的其他元件中施加大量的电子流。这项工作的主要动机是提供这些设备中热效应的变革性知识，最终可以只使用施加的热量来操作，完全消除电荷流。这将使未来设备的简化和尺寸进一步缩小，从而显著推进数据存储和其他技术。金属非局部自旋阀是产生和研究纯自旋电流的一种非常宝贵的装置，尽管人们对它的了解还不够透彻。在NLSV中使用电荷电流产生自旋电流是在15年前实现的，这些传感器准备在近期的磁记录中发挥重要作用。然而，自旋的电注入会引起显著的加热和热电效应，这些效应强烈地影响传感器的性能，目前还没有很好地表征和理解。通过纯热效应在非局部自旋阀中进行自旋注入的演示更令人感兴趣。这些最新和新颖的测量为实现这种没有大电荷电流的传感器指明了方向，这为信息技术界所要求的更小、更敏感的传感器或更有效的源提供了许多优势。该项目利用了在纳米级系统中创建和测量热梯度以及测量塞贝克和珀尔帖效应方面的独特专业知识，以了解和控制金属纳米磁性器件中的热和自旋流。利用微机械热隔离平台直接测量纳米级器件薄膜成分的热性能（导热系数、塞贝克系数和珀尔帖系数）的独特能力是该项目的核心焦点。通过从纳米级器件或薄膜下去除块状衬底，热流方向的不确定性大大减少，通过有限元方法对结构进行建模变得更加简单，并且可以设计应用于纳米级结构的热梯度。具体任务包括：1)了解自旋依赖塞贝克效应和绝对塞贝克效应的界面和材料依赖性；2)寻找磁振子阻力贡献；3)研究“零衬底”器件中的热电效应和自旋注入；4)通过外部热梯度对传感器的热工程响应。

The electronic and magnetic devices that currently enable rapid information processing and massive data storage are formed in part using metallic structures with dimensions approaching 100 nanometers. Often these devices function due to an applied flow of electrons, and this charge flow generates heat. In many cases this heat limits the performance of these tiny devices and prevents gains in technology. This project aims to explore ways to simultaneously avoid or exploit this heating by study of thermal effects in a particular nanoscale metallic magnetic device known as a non-local spin valve. These devices are already known to allow generation of flows of angular momentum, or spin, in a metallic nanowire with no associated charge flow. However, their operation usually requires large applied electron flows in other elements of the device. The main motivation of this work is to provide the transformative knowledge of thermal effects in these devices that could eventually allow operation with only applied heat, eliminating the charge flow altogether. This will enable simplification and further size reduction in future devices that could significantly advance data storage and other technologies.The metallic non-local spin valve is an invaluable, though still not thoroughly understood, device for producing and studying pure spin currents. The use of charge currents to produce spin currents in the NLSV was achieved ~15 years ago, and these sensors are poised to play an important role in near-term magnetic recording. However, the electrical injection of spin causes significant heating and thermoelectric effects that strongly affect the performance of the sensors are not yet well characterized and understood. The demonstration of spin injection in the non-local spin valve via purely thermal effects is of even greater interest. These very recent and novel measurements point the way toward implementation of such sensors without the large charge current, which offer many advantages for the ever smaller and more sensitive sensors or more efficient sources demanded by the information technology community. This project takes advantage of unique expertise in creating and measuring thermal gradients and in measuring Seebeck and Peltier effects in nanoscale systems to understand and control heat and spin flow in metallic nanomagnetic devices. The unique ability to directly measure the thermal properties (thermal conductivity, Seebeck, and Peltier coefficients) of the thin film constituents of nanoscale devices using micromachined thermal isolation platforms is a central focus of the project. By removing the bulk substrate from beneath a nanoscale device or thin film, the uncertainty in the direction of heat flow is dramatically reduced, modeling the structure via finite element methods becomes much simpler, and engineering the thermal gradients applied to the nanoscale structures is possible. Specific tasks include: 1) Understanding interface and materials dependence of the spin-dependent Seebeck effect and the absolute Seebeck effect, 2) the Search for magnon-drag contributions, 3) Studies of thermoelectric effects and the spin injection in "zero substrate" devices, and 4) Thermally engineering response of sensors via external thermal gradients.