Spin Polarized Current in Magnetic Nanostructures

磁性纳米结构和未来磁电子器件的发展关键取决于铁磁层的实质性自旋极化（自旋向上和自旋向下电子数量的差异），控制铁磁元件开关的能力，以及自旋极化传导和自旋极化电流的影响。本提案的重点是磁性纳米结构中自旋极化电流的一些关键方面。自旋扩散长度在金属，半导体，和点接触隧道结将测量使用点接触自旋光谱学。还将详细研究半金属CrO2和Fe3O4中自旋极化的温度依赖性。本提案的第二个方面是研究传统铁磁体和半金属中新发现的自旋转移转矩效应。这些研究将使用单层铁磁性材料和由非磁性、铁磁性和超导薄膜组成的多层铁磁性材料。首席研究员和两名女研究生（其中一名是非裔美国人）将在约翰霍普金斯大学进行拟议的研究。除了在电路中形成电流的电荷之外，由于一种叫做自旋的固有特性，电子还可以表现得像微小的磁铁。推动现代科技进入电子时代的传统电子设备只利用电子的电荷。新一代的磁电子（或自旋电子）设备操纵电子的电荷和自旋。磁电子器件不仅控制电流，还控制自旋极化电流，其中载流电子的自旋非常对齐。一个众所周知的磁电子设备已经应用于我们所有的计算机中，那就是硬盘驱动器中的读头，它是由具有巨大磁阻的材料制成的。未来磁电子设备的发展关键取决于人们如何利用和控制电子在设备中传输时的自旋。这个提议的一个主要方面是开发和表征能够产生大量自旋极化电流的材料。这些材料有望成为磁电子学的基础材料，就像传统电子学中的硅一样。由于自旋极化电流同时携带电流和自旋电流，因此可以观察到传统电子器件所没有的新效应。在此提议期间，自旋极化电流在磁性纳米结构中传播时的影响将被研究。首席研究员一直在积极招募女性和其他少数族裔学生。特别是，两位女研究生，其中一位是非洲裔美国人，将在这个项目中与首席研究员一起工作。

The developments in magnetic nanostructures and future magnetoelectronic devices depend crucially on the substantial spin polarization (the difference in the number of spin-up and spin-down electrons) of the ferromagnetic layer, the ability to control the switching of the ferromagnetic component, as well as effects due to spin-polarized conduction and spin-polarized current. This proposal focuses on some of the key aspects of spin-polarized currents in magnetic nanostructures. The spin diffusion lengths in metals, semiconductors, and point-contact tunnel junctions will be measured using Point-Contact Spin Spectroscopy. The temperature dependence of spin polarization in half-metallic CrO2 and Fe3O4 will also be studied in detail. The second aspect of this proposal is the investigation of the newly discovered spin-transfer torque effects in conventional ferromagnets and half-metals. Single layers of ferromagnetic materials and multilayers made up of non-magnetic, ferromagnetic and superconducting thin films will be used for these studies. The principal investigator and two female graduate students (one of whom is an African American) will carry out the proposed research at Johns Hopkins University.In addition to their electrical charge, the transport of which forms a current in an electrical circuit, electrons can also behave as tiny magnets due to an intrinsic property called spin. Traditional electronic devices, which have propelled modern technology to the electronic age, utilize only the charge of the electron. The new generation of magnetoelectronic (or spintronic) devices manipulates both charge and spin of the electron. Instead of just electrical current, magnetoelectronic devices manipulate spin-polarized current, in which the spins of the current-carrying electrons are very much aligned. One well-known magnetoelectronic device that has already perpetrated in all our computers, is the read-heads in hard drives made using materials that have enormous magnetoresistance. The development of future magnetoelectronic devices depends crucially on how one can harness and control the spins of the electrons as they are transported through devices. One major aspect of this proposal is the development and characterization of materials that can generate copious amounts of spin-polarized current. These materials hold promise as the basic materials in magnetoelectronics in a manner similar to that of silicon in traditional electronics. Because a spin-polarized current carries both electrical current and spin current, new effects, which are absent in traditional electronic devices are observed. During this proposal period, the effects of a spin-polarized current as it propagates through magnetic nanostructures will be studied. The principal investigator has been actively recruiting women and other minority students. In particular, two female graduate students, one of whom is an African American, will work with the principal investigator in this project.