Spin Pumping in Ferromagnet-Semiconductor Heterostructures

非技术摘要：铁等磁性材料是计算机硬盘等存储技术的基础，而硅等半导体是大量微电子器件的基础。 该项目解决了如何将这两种非常不同类型的材料结合起来以创建具有新功能的电子设备的基本问题，包括在单个芯片上集成存储器和处理功能。 为了帮助实现这一目标，首席研究员和他的团队研究了一个过程，在这个过程中，使用微波将信息从磁性材料传输到半导体，微波是手机等应用中使用的波类型。 微波被用作“泵”，以产生从磁性材料到半导体的自旋流（信息载体）。 该项目确定了这一过程的效率以及如何在半导体内部检测自旋流。 通过使用微波而不是由电池产生的普通电流，可以提高这些设备的操作速度。 探索了用于将自旋转移到半导体中的新磁性材料，也允许在更高温度下更有效地操作。 除了推进可用于信息处理的技术外，该项目还培训本科生和研究生制造和测量这类新电子器件的技术。技术摘要：半导体提供了一个独特的环境，可以使用电场和磁场来控制自旋极化载流子，但是将自旋从铁磁材料转移到半导体是一个重大挑战。 该项目开发了一种在微波频率下将自旋从金属铁磁体直接转移到半导体中的方法。这种方法被称为自旋抽运，已经有效地应用于金属，但尚未在半导体的情况下进行定量测试。这项工作利用了在将高度极化的Heusler合金铁磁体与III-V族半导体集成的设备中产生和检测自旋极化载流子的最新进展。这些异质结构进行了优化，在微波频率下的操作，和自旋泵的方法，然后定量比较与建立自旋输运技术，包括非本地自旋阀和自旋霍尔效应测量。 控制自旋抽运机制的重要参数，包括界面混合电导和自旋霍尔角，将被独立测量。 通过改变铁磁-半导体界面，允许自旋注入到具有强自旋-轨道相互作用的系统中，提高了自旋泵浦效率。该计划的最终目标是证明在一个二维电子系统中，由自旋泵从铁磁体驱动的自旋电流到电荷电流的转换。 这就要求器件从GaAs基异质结构开始，向InAs量子威尔斯发展。

Non-Technical Abstract:Magnetic materials such as iron form the basis of storage technologies such as computer hard disks, while semiconductors such as silicon are the foundation of a vast array of microelectronic devices. This project addresses the fundamental question of how these two very different types of materials can be combined to create electronic devices with new capabilities, including the integration of memory and processing functions on a single chip. To help accomplish this, the principal investigator and his team investigate a process in which information is transferred from the magnetic material to the semiconductor using microwaves, which are the types of waves used in applications such as cellphones. The microwaves are used as a "pump" to generate a flow of spin (the carrier of information) from the magnetic material into the semiconductor. The project determines how efficient this process is and how the flow of spin can be detected inside the semiconductor. By using microwaves instead of an ordinary current generated by a battery, the speed of these devices operate can be enhanced. New magnetic materials for transferring spin into the semiconductor are explored, also allowing for more efficient operation at higher temperatures. In addition to advancing a technology that can be used in information processing, the project trains undergraduate and graduate students in techniques for fabricating and measuring this new class of electronic devices.Technical Abstract:Semiconductors provide a unique environment for controlling spin-polarized carriers using electric and magnetic fields, but the transfer of spin from ferromagnetic materials into semiconductors is a significant challenge. This project develops a means to transfer spins directly from a metallic ferromagnet into a semiconductor at microwave frequencies. This approach, known as spin pumping, has been applied effectively to metals, but it has not yet been tested quantitatively in the case of semiconductors. The effort exploits recent advances in the generation and detection of spin-polarized carriers in devices integrating highly-polarized Heusler alloy ferromagnets with III-V semiconductors. These heterostructures are optimized for operation at microwave frequencies, and the spin pumping approach is then compared quantitatively with established spin transport techniques, including non-local spin valve and spin Hall effect measurements. The important parameters governing the spin-pumping mechanism, including the interfacial mixing conductance and spin Hall angle, are to be measured independently. The spin pumping efficiency is enhanced by modifying the ferromagnet-semiconductor interface, allowing for spin injection into systems with strong spin-orbit interaction. The ultimate goal of the program is to demonstrate the conversion of a spin current to a charge current in a two-dimensional electron system that is driven by spin pumping from a ferromagnet. This requires a progression of devices starting in GaAs-based heterostructures and moving towards InAs quantum wells.