Enabling Breakthroughs with Large Moment Magnetic Films

非技术性摘要。磁性材料在信息处理、计算和数据存储方面继续取得重大进展。磁性材料最重要的特性之一是磁矩的大小，这往往是阻碍进一步改进的主要限制因素。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，所能达到的最大磁矩只增加了很少的量。在NSF材料研究部固态和材料化学计划的支持下，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显著增加了30%。只有将这些磁性合金生长成具有特定晶体结构的薄膜，才能实现这些大的力矩。有趣的是，这些具有这些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。通过这些研究提高了对薄膜中磁性的理解深度，这与几乎任何结合了用于磁记录、自旋产生、自旋操纵和/或自旋检测的超薄磁性薄膜或多层分层结构的技术应用有关。对不稳定的薄膜生长的理解，以及在该项目期间产生这些稳定结构的过程，可以对依赖于薄膜结构的其他领域产生影响。例如，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，以及能源生成和存储材料的进步。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射线技术和电磁表征技术的培训，这些技术已经被证明是工业、实验室和学术环境中生产性科学职业的优秀培训。来自蒙大拿州七个保留地之一的几名美国原住民高中生通过伊泽达教授参与蒙大拿州学徒计划(MAP)参与了这项研究。技术摘要。高扭矩合金薄膜的形成通常包括掺入具有大扭矩的过渡金属元素。该项目得到美国国家科学基金会材料研究部固态和材料化学计划的支持，研究了体心立方FeCo基三元合金(FeCoMn和FeCoCr三元合金)的磁性，以制备平均磁矩明显大于(30%)斯莱特-鲍林极限值2.45Mub/原子的薄膜。磁矩和磁各向异性由振动样品磁测、铁磁共振和磁圆二向色性确定。薄膜成分由能量积分X射线吸收光谱确定。以前已经观察到Fe10Co60Mn30薄膜在成分空间的稀疏样本数据集中的平均原子矩(由XMCD确定)为3.25Mub/ATOM，这项研究建立在这一令人兴奋的发现的基础上。此外，Pi和他的团队还研究了观察到的Mn矩随成分变化而崩塌的机制。大磁矩材料在高密度存储应用、自旋扭矩分级、BH能量积器件结构、控制纳米尺度非共线磁体中的旋量应用以及建立增强的电子自旋极化等方面尤为重要。提高薄膜的平均原子矩可以显著提高薄膜的性能。此外，由于薄膜/晶格失配造成的维度降低和结构扭曲，外延超薄膜提供了通过改变磁性来控制自旋输运性能的机会。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.