Enabling Breakthroughs with Large Moment Magnetic Films

非技术总结。磁性材料在信息处理、计算和数据存储方面不断取得重大进展。磁性材料最重要的特性之一，往往是阻碍进一步改进的主要限制因素，是磁矩的大小。任何显著的增长都被认为是信息技术中无处不在的磁性应用的重要成就。不幸的是，近一个世纪以来，能达到的最大磁矩只上升了一点点。在这个由NSF材料研究部固态和材料化学项目支持的项目中，Idzerda教授和他的研究小组探索了最近发现的一组磁性合金，这些合金的最大磁矩值增加了30%。只有将这些磁性合金生长成具有特定晶体结构的薄膜，才能实现这些大力矩。有趣的是，这些具有这种晶体结构的合金在整体上是不稳定的，这解释了为什么直到现在才观察到这些大磁矩。这些研究增加了对薄膜磁性的深入了解，这与几乎所有将超薄磁性薄膜或多层分层用于磁记录、自旋产生、自旋操纵和/或自旋检测的技术应用有关。了解不稳定的薄膜是如何生长的，以及在这个项目中产生这些稳定结构的过程，可以对依赖薄膜结构的其他领域产生影响。例子包括太阳能电池的更高性能和更高效率，导致新电池突破的组件，以及能源产生和存储材料的进步。该项目还为本科生和研究生提供先进的真空沉积技术、薄膜沉积方法、x射线技术和电子/磁性表征技术方面的培训，这些技术已经被证明是在工业、实验室和学术环境中从事生产性科学职业的优秀培训。几名来自蒙大拿七个保留区之一的美国原住民高中生通过伊泽达教授参与的蒙大拿学徒计划（MAP）参与了这项研究。技术总结。高矩合金薄膜的建立通常包括加入具有大矩的过渡金属元素。该项目由美国国家科学基金会材料研究部固态与材料化学项目资助，研究了bcc feo基三元合金（FeCoMn和FeCoCr）的磁性能，建立了平均磁矩显著大于Slater-Pauling极限值2.45 muB/原子（30%）的薄膜。磁矩和磁各向异性由振动样品磁强计、铁磁共振和磁圆二色性测定。薄膜成分由能量积分x射线吸收光谱测定。Fe10Co60Mn30薄膜的平均原子矩为3.25 muB/原子（由XMCD确定），在一个稀疏的组成空间样本数据集中进行矩映射，之前已经观察到，本研究建立在这一令人兴奋的发现之上。此外，PI和他的团队还研究了观察到的Mn矩坍塌随成分变化的机制。大磁矩材料在高密度存储应用、自旋扭矩层次、bh能量积器件结构、纳米尺度非共线磁体中自旋体应用的控制以及建立增强的电子自旋极化方面尤为重要。增加这些薄膜的平均原子矩可以显著提高它们的性能。此外，外延超薄膜由于薄膜/晶格不匹配造成的维数降低和结构扭曲，通过改变磁性能，为自旋输运性能控制提供了机会。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical Summary. Magnetic materials continue to make significant advances in information processing, computation, and data storage. One of the most important characteristics of magnetic materials, and often a major limiting factor preventing further improvements, is the size of the magnetic moment. Any significant increase is recognized as an important achievement for magnetic applications that are ubiquitous in information technologies. Unfortunately, for nearly a century the maximum magnetic moment that can be achieved has only risen by a small amount. With this project, supported by the Solid State and Materials Chemistry program in NSF's Division of Materials Research, Prof. Idzerda and his research group explore a recently discovered group of magnetic alloys that show a remarkable 30% increase in the value of the maximum magnetic moment. Only by growing these magnetic alloys as a thin film of a specific crystal structure can these large moments be realized. Intriguingly, these alloys with these crystal structures are unstable in the bulk, explaining why these large magnetic moments were not observed until now. The increased depth of understanding of magnetism in thin films resulting from these studies is relevant to almost any technological applications that incorporate ultrathin magnetic films or multilayer hierarchies for magnetic recording, spin generation, spin manipulation and/or spin detection. The understanding of how growth of thin films that are not stable in the bulk, and the processes created during this project to generate these stable structures, can have an impact in other fields that rely on thin film structures. Examples include higher performance and better efficiencies in solar cells, the components leading to new battery breakthroughs, and advances in energy generation and storage materials. This project also provides training of undergraduate and graduate students in advanced vacuum deposition technology, film deposition methods, X-ray techniques, and electronic/magnetic characterization techniques, which have already been demonstrated to be excellent training for productive scientific careers in industrial, laboratory, and academic settings. Several Native American high school students from one of the seven Montana reservations are involved in this research through Prof. Idzerda's involvement in the Montana Apprenticeship Program (MAP). Technical Summary. The establishment of high moment alloy films typically includes the incorporation of transition metal elements that have large moments. This project, supported by the Solid State and Materials Chemistry program in NSF's Division of Materials Research, characterizes the magnetic properties of bcc FeCo-based ternary alloys (FeCoMn and FeCoCr) to establish thin films with average magnetic moments significantly larger (30%) than the Slater-Pauling limit value of 2.45 muB/atom. The magnetic moments and magnetic anisotropy are determined by vibrating-sample magnetometry, ferromagnetic resonance, and magnetic circular dichroism. The film compositions are determined from energy integrated X-ray absorption spectroscopy. An average atomic moment for an Fe10Co60Mn30 film with a moment of 3.25 muB/atom (as determined by XMCD) in a sparse sample data set of the compositional space for moment mapping has been observed previously, and this research builds on this exciting finding. In addition, the PI and his group investigate the mechanism for the observed Mn moment collapse with composition variation. Large magnetic moment materials are particularly important in high-density memory applications, spin torque hierarchies, BH-energy product device structures, control of spinor applications in nanoscale non-collinear magnets, and establishing enhanced electron spin-polarizations. Increasing the average atomic moment of these films can significantly improve their performance. In addition, epitaxial ultrathin films offer opportunities in spin-transport performance control through the modification of magnetic properties due to the reduced dimensionality and structural distortions created by film/lattice mismatches.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.