Acquisition of a New Mossbauer Spectrometer and Associated Equipment

该奖项为密苏里大学罗拉分校莫斯堡尔效应实验室的仪器提供部分支持。购买的仪器分为穆斯堡尔光谱仪、液氦低温恒温器和工作温度为15 K的机械制冷机三部分，将用于材料研究和学生教育。在过去的几年里，通过NSF资助的研究，在了解氮化R2Fe17化合物的结构、电子和磁性方面取得了重大进展，这些化合物具有成为硬磁性材料的潜力。作为这项工作的一部分，建立了一个模型来分析R2Fe17和R2Fe17Nx化合物的穆斯堡尔光谱，这个模型是基于铁的近邻环境和这些材料中单个晶体学位点的Wigner-Seitz细胞体积。还研究了叔原子对R2Fe17化合物的电子和磁性能的影响。在这些材料中，叔原子导致居里温度和室温磁矩的急剧增加。这两种增长对于开发新的永磁材料都是重要的。本研究的长期目标是相互关联，对于各种材料，具有明确定义的Wigner-Seitz细胞体积，近邻环境和穆斯堡尔光谱超精细参数的特定铁位点的微观电子和磁性能。这需要对复杂的、分辨率良好的穆斯堡尔光谱进行仔细、一致的分析，我们已经在R2Fe14B和R2Fe17化合物的研究中证明了这一能力。随着这项工作扩展到新的体系，预计将开发不同系列化合物中不同铁位点之间的有用相关性，这种相关性将证明对理解当前和未来的含铁硬磁材料是非常宝贵的。除了研究金属间化合物外，新的穆斯堡尔光谱仪还将用于其他几个领域的研究。这些研究包括对一系列具有非常有前途的热电性能的填充方晶石CeFe4-xCoxSb12的晶格动力学特性的详细研究。其他工作将涉及有机铁配合物，并将研究具有可变电子转移速率和含二茂铁的热致液晶的系统。未来的其他工作将涉及极细颗粒氧化铁，这是新的药物输送系统中重要的材料。最初的工作表明，这些化合物如预期的那样，具有超顺磁性，阻塞温度对材料的制备方法非常敏感。穆斯堡尔效应将用于确定与不同制剂相关的特定阻断温度和/或阻断温度范围，该结果预计将与药物递送的功效相关。许多涉及氧化铁、地质材料、配位化合物和冶金问题的其他项目将确保新光谱仪在可预见的未来得到广泛的持续使用。%%%***

9802376LongThis award provides partial support for instrumentation for the Mossbauer-effect laboratory at the University of Missouri-Rolla. The instrumentation to be acquired can be divided into three parts, a Mossbauer spectrometer, a liquid helium cryostat, and a mechanical refrigerator for work down to 15 K, and will be used for materials research and education of students.Over the past several years, through NSF funded research, significant progress has been made in understanding the strutural, electronic, and magnetic properties of the nitrided R2Fe17 compounds, compounds with potential as hard magnetic materials. As a part of this work, a model has been developed for the analysis of the Mossbauer spectra of both R2Fe17 and R2Fe17Nx compounds, a model which is based on both the iron near-neighbor environment and the Wigner-Seitz cell volume of the individual crystallographic sites in these materials. The influence of a tertiary atom on the electronic and magnetic properties of the R2Fe17 compounds has also been studied. In these materials the tertiary atom has resulted in a dramatic increase in the Curie temperature and the room temperature magnetic moments. Both these increases are important in developing new permanent magnetic materials.The long-range goal of this research is to intercorrelate, for a variety of materials, the microscopic electronic and magnetic properties of specific iron sites which have well-defined Wigner-Seitz cell volumes, near-neighbor environments, and Mossbauer spectral hyperfine parameters. This requires a careful, consistent analysis of complex well-resolved Mossbauer spectra, a capability which we have demonstrated in our work on the R2Fe14B and R2Fe17 compounds. As this work is extended to the new systems, it is anticipated that useful correlations between the different iron sites in different series of compounds will be developed, correlations which will prove invaluable in understanding both current and future iron-containing hard magnetic materials.In addition to work on intermetallic compounds, the new Mossbauer spectrometer will also be used for studies in several other fields. These studies include detailed investigation of the lattice dynamic properties of a series of filled skutterudites, CeFe4-xCoxSb12, materials with very promising thermoelectric properties. Other work will deal with organoiron complexes and will investigate systems with variable rates of electron transfer and with ferrocene-containing thermotropic liquid crystals. Other future work will deal with extremely fine particle iron oxyhydroxides, materials that are important in new drug delivery systems. Initial work has indicated that these compounds are, as expected, superparamagnetic with blocking temperatures which are very sensitive to the methods of preparation of the materials. The Mossbauer effect will be used to determine the specific blocking temperatures and/or the range of blocking temperatures associated with the different preparations, a result that is expected to be related to the efficacy of the drug delivery. Many other projects dealing with iron oxides, geologic materials, coordination compounds, and metallurgical problems will ensure that the new spectrometer will receive intensive continued use into the foreseeable future.%%%***