Transport Studies of Novel Electronic and Magnetic Materials

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w:\awards\awards96\*.doc 9801738 Zettl This experimental research project focuses on the electronic transport properties of novel collossal magnetoresistance (CMR) manganite perovskite materials. Emphasis is on the electronic, thermal and magnetic properties studied by means of transport annd magnetic measurements. Much of the study will focus on the use of high pressures to which the CMR effect is particularly sensitive. Both teflon-seal and diamond anvil cells will be employed. Isotopic substitution will also be performed, independently and in conjunction with the pressure studies. The aim of the research is to clarify the fundamental interactions, such as polaron formation and dynamics, responsible for the unusual transport and magnetotransport behaviors of these scientifically intriguing and potentially very useful materials. Other materials of interest using the same experimental methods are perovskite superlattices and fullerene polymers. The latter system displays a pressure-induced insulator-metal transition similar to that seen in CMR systems, although the underlying physics is expected to be different. This research program is interdisciplinary in nature and involves several graduate students, who receive excellent training in preparation for careers in industry, government laboratories or academia. %%% This experimental basic research project focuses on the high sensitivity of the electrical resistance of a class of oxide materials to a magnetic field. This effect, which has become known as "colossal magnetoresistance" (CMR) is scientifically interesting and potentially of importance in improved technology. In this situation, the electrical resistance of the material is changed by an applied magnetic field, and such effects, which are usually very small, in these materials are usefully large. An attra ction of a magnetoresistive sensor is that it is more easlily minaturized, simpler, and cheaper to produce, than, say, the coil of wire in many traditional magnetic pickup devices. Magnetic sensors are well known in computer hard drives, magnetic tape recorders and other electronic applications, but are actually widespread in simpler applications like rotation speed sensors (tachometers) and many others. This experimental work focuses on CMR materials in the manganite perovskite class, and seeks to clarify the physical basis for the effect. The experiments concern the electronic, thermal and magnetic properties studied by means of transport and magnetic measurements. Much of the study will focus on the use of high pressures to which the CMR effect is particularly sensitive. Both teflon-seal and diamond anvil cells will be employed. Isotopic substitution will also be performed, independently and in conjunction with the pressure studies. Other materials of interest using the same experimental methods are perovskite superlattices and fullerene polymers. The latter system displays a pressure-induced insulator-metal transition similar to that seen in CMR systems, although the underlying physics is expected to be different. This research program is interdisciplinary in nature and involves several graduate students, who receive excellent training in preparation for careers in industry, government laboratories or academia. ***