Magnetic Phenomena on the Nanometer Scale

本文主要研究了铁磁金属的自旋极化和铁磁元件的开关。这些现象发生在纳米尺度上，对磁电子器件具有至关重要的意义。我们建议使用点接触Andreev反射技术，并进行适当的分析，来测量各种材料的本征自旋极化，特别是CrO2和Heusler合金，它们已经被预测为100%自旋极化。我们还建议解决具有交换偏置的多层中的关键问题，特别是存在的反铁磁自旋结构的类型，反铁磁畴，以及使用合成反铁磁体交换耦合系统的开关。参与该项目的研究生在学术、工业和政府的职业生涯中接受尖端技术的培训。磁电子器件是一种既能控制自旋（磁偶极矩）又能控制电子电荷的新型器件，而传统的电子器件只控制电子电荷。这些新设备主要依赖于某些铁磁材料的实质性自旋极化（流动电子流过的常驻自旋向上和自旋向下电子数量的差异），以及切换铁磁通道磁化的能力。使用这些组件的此类设备的例子包括几乎所有今天制造的计算机中的巨磁电阻（GMR）读头，以及磁性随机存取存储器（MRAM），有朝一日可能取代当前计算机中使用的动态随机存取存储器（DRAM）。这项工作的目的是利用安德烈夫反射技术测量金属（铁磁通道）的固有自旋极化，这取决于实验中使用的超导结的基本特性。这项工作的另一部分是了解存在于许多磁电子设备中的薄磁层如何通过一个小的外场轻松切换，或者设计成抵抗切换。该课程的学生将接受物理、新材料和测量技术方面的广泛培训，使他们能够在学术界、工业和政府实验室中从事职业。

This research is focused on the investigation of the spin polarization of ferromagnetic metals and the switching of ferromagnetic components. These phenomena, occurring on the nanometer scale, are of crucial importance to magnetoelectronic devices. We propose to use the point-contact Andreev reflection technique, with appropriate analyses, to measure the intrinsic spin polarization of a variety of materials, especially CrO2 and the Heusler alloys, which have been predicted to be 100% spin polarized. We also propose to address key issues in multilayers with exchange bias, particularly the type of antiferromagnetic spin structure present, antiferromagnetic domains, and the switching of exchange-coupled systems using synthetic antiferromagnets. The graduate students involved in the project receive training in cutting-edge technology of careers in academe, industry and government.Magnetoelectronic devices are new devices that manipulate both spin (magnetic dipole moment) and charge of electrons as opposed to only charge of electrons in traditional electronic devises. These new devices depend crucially on the substantial spin polarization of certain ferromagnetic materials (a difference in the number of resident spin-up and spin-down electrons) through which the itinerant electrons flow, and the ability to switch the magnetization of the ferromagnet channels. Example of such devices employing these components include giant magnetoresistance (GMR) read-heads in virtually all computers manufactured today, and magnetic random access memories (MRAM) that one day may be replace the current dynamic random access memory (DRAM) used in current computers. This work is directed at measuring the intrinsic spin polarization of metals (the ferromagnetic channels) using the technique of Andreev reflection, which depends on fundamental properties of superconducting junctions that are employed in the experiments. The other part of this work is to understand how thin magnetic layers, which exist in many magnetoelectronic devices, can be made to switch easily by a small external field, or be designed to resist switching. Students in this program will receive extensive training in physics, new materials, and measuring techniques to enable them to pursue careers in academe, as well as in industrial and government labs.