Physics near the metal-insulator transition in magnetic thin-films

*技术摘要*对于传统的过渡金属带铁磁体(Fe，Co和Ni)，其中排列的力矩成功地由不相等的多数(自旋向上)和少数(自旋向下)带描述，当巡回被无序破坏到在临界无序时电导率下降到零的程度时，磁性的最终命运是未知的。本项目致力于系统地减小二维(2D)磁性薄膜的厚度(从而增加无序强度)直到达到绝缘磁性状态的后果。定制的高真空沉积系统具有原位电/磁表征能力，可防止样品因空气暴露而变质，这对这项工作至关重要。该项目的重点是通过临界无序调整各种磁系统，预计将为薄膜磁性绝缘体的性质提供有价值的见解，并有助于回答以下问题：(1)无序导致电子在自旋波上的高非弹性散射，(2)局部磁矩的有序性，(3)粒度的作用，以及(4)新相的出现。该项目将支持对博士生进行先进真空沉积和电磁表征技术的教育，这些技术已被证明是在学术和技术环境中从事生产性科学职业的极佳培训。这些研究的开展将改善对超薄磁性材料磁性的预测，并扩大对在表面和界面经历的非常不同的环境中体磁行为的了解。*非技术摘要*过渡金属元素(如铁)的磁性尚不完全了解。在巡回(行进)电子的情况下，向上自旋(北极向上)的电子比向下(北极向下)自旋的电子更多，净差异产生了磁性，例如，导致铁指南针与地球磁场对准。当巡回电子从杂质和/或缺陷上散射时，情况迅速变得更加复杂，失去了它们的巡回性，并最终在无序强度处于临界值时成为局域化(固定在适当的位置)。本项目将进行磁性薄膜的实验研究，在其中可以系统地增加无序度，并研究其对磁性的影响。在临界无序时，磁性金属失去了巡回性，成为具有局域电子的绝缘体，并可能出现具有不寻常自旋排列的新磁相。该项目将支持对博士生进行先进真空沉积和电磁表征技术的教育，这些技术已被证明是在学术和技术环境中从事生产性科学职业的极佳培训。通过这些研究预期增加对薄膜中磁性的物理理解将与将超薄磁性薄膜结合到多层结构中用于磁记录、自旋产生、自旋操纵和/或自旋检测的技术应用相关。

****Technical Abstract****For the traditional transition-metal band ferromagnets (Fe, Co and Ni) where the aligned moments are successfully described by unequally populated majority (spin-up) and minority (spin-down) bands, the ultimate fate of magnetism, when the itinerancy is compromised by disorder to such an extent that the conductivity drops to zero at critical disorder, is unknown. This project addresses the consequences of systematically reducing the thickness of two-dimensional (2D) magnetic thin films (thereby increasing disorder strength) until the insulating magnetic state is attained. A custom high-vacuum deposition system with in situ electronic/magnetic characterization capability prevents sample deterioration due to air exposure and is essential for this work. The project's focus on tuning a variety of magnetic systems through critical disorder is expected to provide valuable insight into the properties of thin-film magnetic insulators and help answer questions about (1) the disorder induced high rate of inelastic scattering of electrons off of spin waves, (2) the ordering of local moments, (3) the role of granularity, and (4) the emergence of new phases. This project will support the education of PhD students in advanced vacuum deposition and electronic/magnetic characterization techniques, which have already proven to be excellent training for productive scientific careers in academic and technology settings. Pursuit of these studies will improve prediction of the magnetic properties of ultrathin magnetic materials and extend knowledge of the behavior of bulk magnetism in the very different environments experienced at surfaces and interfaces.****Non-Technical Abstract****Magnetism in the transition metal elements such as iron is not fully understood. In the itinerant (traveling) electron scenario there are more spin-up (north pole up) than spin down (north pole down) electrons and the net difference gives rise to the magnetic properties that, for example, cause an iron compass needle to align with the earth's magnetic field. The situation rapidly becomes more complicated when the itinerant electrons scatter off impurities and/or defects, losing their itinerancy and eventually becoming localized (fixed in place) when the disorder strength, as characterized by the density of scattering sites, is at a critical value. This project will pursue experimental studies of magnetic thin films in which disorder can be systematically increased and the effect on magnetism studied. At critical disorder, itinerancy is lost and the magnetic metal becomes an insulator with localized electrons accompanied by the likely appearance of new magnetic phases with unusual spin alignments. This project will support the education of PhD students in advanced vacuum deposition and electronic/magnetic characterization techniques, which have already proven to be excellent training for productive scientific careers in academic and technology settings. The expected increased physical understanding of magnetism in thin films from these studies will be relevant to technological applications which incorporate ultrathin magnetic films into multilayer configurations for magnetic recording, spin generation, spin manipulation and/or spin detection.