Acquisition of a New Mossbauer Spectrometer and Associated Equipment

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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.%%%***