Magnetic Correlations and Control in Nanoscaled Molecule-based Magnets

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****Technical Abstract****This research explores the interplay between the electromagnetic and structural properties of cyanometallate coordination polymers. Specially, the fabrication of heterostructured films and particles increases the interface to bulk ratio, thereby allowing the stress/strain effects at the boundaries between the constituents to dominate the properties. Notably, irradiation with light allows persistent photocontrol of the magnetism up to liquid nitrogen temperatures, and this work seeks to explore different paths to extend this property to room temperature. In parallel, quantum spin chains will also be studied, and the emphasis is placed on S = 2 materials. The boundary between quantum and classical spins in one-dimension will be probed, and the influence of the anisotropy of the local magnetic environment will be explored. Both research thrusts will employ pressure as an external parameter, and these molecule-based magnets are significantly more pliable than their traditional solid-state counterparts. Physics and chemistry graduate students participate directly in every aspect of the research program and receive unique training in a variety of techniques, including magnetometry, X-ray and neutron scattering, and high-field, high-frequency magnetic resonance techniques. The tools are available in the local laboratories of the investigators or at national facilities like the National High Magnetic Field Laboratory (NHMFL), and the Spallation Neutron Source (SNS) and High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL).****Non-Technical Abstract****The discovery of novel phenomena and the development of new devices have now reached levels of maturity where increasingly complex materials are required as constituents of nanometer sized films and particles. Along this direction, molecule-based magnets are excellent materials because their properties can be tuned by synthesis protocols and controlled by external stimuli such as temperature, magnetic field, pressure/stress/strain, and irradiation by light. In this research program, materials historically generated as paint pigments are modified and employed in nanoscaled films and particles whose novel magnetic and optical properties can be externally controlled. The sensitive response results from stress and strain developed at the interface between the different constituents, and the nanometer length scales are required to diminish the static background that the bulk material contributes. The research seeks to extend this control to higher temperatures and in novel morphologies that can provide new magneto-optical switches and light harvesting devices. A variety of interdisciplinary tools, including magnetometry, electron microscopy, X-ray scattering, and magnetic resonance, are used to characterize the samples. Physics and chemistry graduate students are trained using state-of-the-art instrumentation and data analysis techniques, and undergraduate students are integrated into various aspects of the work. Ultimately, the goal is to increase the knowledge of the interplay between magnetic and electronic interactions in environmentally sensitive materials that are inexpensive to generate.