Spin Polarized Current in Magnetic Nanostructures

磁性纳米结构和未来磁电子器件的发展在很大程度上取决于铁磁层的实质性自旋极化(自旋向上和向下的电子数目的差异)、控制铁磁分量切换的能力以及自旋极化传导和自旋极化电流的影响。这一提议集中在磁性纳米结构中自旋极化电流的一些关键方面。金属、半导体和点接触隧道结中的自旋扩散长度将使用点接触自旋谱进行测量。还将详细研究半金属CrO_2和Fe_3O_4中的自旋极化与温度的关系。这一建议的第二个方面是研究新发现的在传统铁磁体和半金属中的自旋转移扭矩效应。这些研究将使用单层铁磁材料和由非磁性、铁磁性和超导薄膜组成的多层膜。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·霍普金斯大学开展这项拟议中的研究。除了电荷在电路中形成电流外，电子还可以像微小的磁铁一样，因为一种名为自旋的本征性质。将现代技术推向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(或自旋电子学)装置可以同时操纵电子的电荷和自旋。不只是电流，磁电子设备操纵的是自旋极化电流，在这种电流中，载流电子的自旋非常对准。一种众所周知的磁电子设备，已经在我们所有的计算机中制造，就是硬盘驱动器中的读取头，它使用的材料具有巨大的磁阻。未来磁电子设备的发展关键取决于人们如何在电子通过设备传输时利用和控制电子的自旋。这一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中的基础材料，其方式类似于传统电子学中的硅。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中没有的新效应。在这一建议期间，将研究自旋极化电流在磁性纳米结构中传播时的影响。首席调查员一直在积极招募妇女和其他少数族裔学生。特别是，两名女研究生，其中一名是非裔美国人，将在这个项目中与首席调查员合作。

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.