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），其中排列力矩被不均匀地描述为多数（自旋向上）和少数（自旋向下）带，当游程受到无序损害以至于电导率在临界无序下降至零时，磁性的最终命运是未知的。该项目解决了系统地减少二维（2D）磁性薄膜厚度（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子/磁性表征能力，可防止样品因空气暴露而变质，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性系统，预计将为薄膜磁性绝缘体的特性提供有价值的见解，并有助于回答以下问题：(1)无序诱导自旋波电子的高非弹性散射率，(2)局部矩的排序，(3)粒度的作用，以及(4)新相的出现。该项目将支持博士研究生在先进的真空沉积和电子/磁性表征技术方面的教育，这些已经被证明是在学术和技术环境中富有成效的科学事业的优秀培训。这些研究将改善超薄磁性材料的磁性预测，并扩展对表面和界面在不同环境下体磁性行为的认识。****非技术摘要****磁性在过渡金属元素，如铁是不完全了解。在流动电子的情况下，向上自旋（北极向上）的电子比向下自旋（北极向下）的电子多，这种净差产生了磁性，例如，使铁罗盘指针与地球磁场对齐。当以散射点密度为特征的无序强度达到临界值时，当流动电子将杂质和/或缺陷散射出去，失去其流动性并最终本地化（固定在原位）时，情况会迅速变得更加复杂。本项目将进行磁性薄膜的实验研究，其中无序可以系统地增加，并研究对磁性的影响。在临界无序状态下，流动性丧失，磁性金属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。该项目将支持博士研究生在先进的真空沉积和电子/磁性表征技术方面的教育，这些已经被证明是在学术和技术环境中富有成效的科学事业的优秀培训。这些研究增加了对薄膜磁性的物理理解，这将与将超薄磁性薄膜纳入多层结构的技术应用有关，用于磁记录、自旋产生、自旋操纵和/或自旋检测。

****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.