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），其中对齐的时刻被成功地描述为不均匀填充的多数（自旋向上）和少数（自旋向下）带，磁性的最终命运是未知的，当无序损害到这样的程度时，电导率在临界无序时下降到零。该项目解决了系统地减少二维（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子/磁性表征能力，可防止样品因暴露在空气中而劣化，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，并帮助回答有关以下问题：（1）无序引起的电子非弹性散射的高速率自旋波，（2）局部矩的排序，（3）粒度的作用，以及（4）新相的出现。该项目将支持博士生在先进的真空沉积和电子/磁性表征技术的教育，这已经被证明是在学术和技术环境中生产性科学职业的优秀培训。这些研究的追求将改善对磁性材料磁性的预测，并扩展对表面和界面处经历的非常不同的环境中的体磁性行为的认识。非技术摘要 * 铁等过渡金属元素的磁性尚未完全了解。在巡回（旅行）电子的情况下，有更多的自旋（北极向上）比自旋（北极向下）电子和净差异产生的磁性，例如，导致铁罗盘针与地球的磁场对齐。当巡游电子从杂质和/或缺陷上散射时，情况迅速变得更加复杂，失去了它们的巡游性，并最终在无序强度（由散射位点的密度表征）处于临界值时变得局部化（固定在适当位置）。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，巡回性消失，磁性金属变成绝缘体，局部电子伴随着可能出现的新的磁相，具有不寻常的自旋排列。该项目将支持博士生在先进的真空沉积和电子/磁性表征技术的教育，这已经被证明是在学术和技术环境中生产科学职业的优秀培训。从这些研究中预期增加的物理理解的磁性薄膜将是相关的技术应用，将磁性薄膜纳入磁记录，自旋产生，自旋操纵和/或自旋检测的多层结构。

****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.