Yeh, N.-C. and Vasquez, R. P. and Beam, D. A. and Fu, C.-C. and Huynh, J. and Beach, G. (1997) Effects of lattice distortion and Jahn–Teller coupling on the magnetoresistance of La0.7Ca0.3MnO3 and La0.5Ca0.5CoO3 epitaxial films. Journal of Physics: Condensed Matter, 9 (18). pp. 3713-3721. ISSN 0953-8984 http://resolver.caltech.edu/CaltechAUTHORS:YEHjpcd97
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Studies of La0.7Ca0.3MnO3 epitaxial films on substrates with a range of lattice constants reveal two dominant contributions to the occurrence of colossal negative magnetoresistance (CMR) in these manganites: at high temperatures (T → TC, TC being the Curie temperature), the magnetotransport properties are predominantly determined by the conduction of lattice polarons, while at low temperatures (T ≪ TC/, the residual negative magnetoresistance is correlated with the substrate-induced lattice distortion which incurs excess magnetic domain wall scattering. The importance of lattice polaron conduction associated with the presence of Jahn–Teller coupling in the manganites is further verified by comparing the manganites with epitaxial films of another ferromagnetic perovskite, La0.5Ca0.5CoO3. Regardless of the differences in the substrate-induced lattice distortion, the cobaltite films exhibit much smaller negative magnetoresistance, which may be attributed to the absence of Jahn–Teller coupling and the high electron mobility that prevents the formation of lattice polarons. We therefore suggest that lattice polaron conduction associated with the Jahn–Teller coupling is essential for the occurrence of CMR, and that lattice distortion further enhances the CMR effects in the manganites.
|Additional Information:||© Institute of Physics and IOP Publishing Limited 1997. Received 10 October 1996. Print publication: Issue 18 (5 May 1997) The research at Caltech is supported by the Packard Foundation and the National Aeronautics and Space Administration (NASA). Part of the research was performed by the Center for Space Microelectronics Technology, Jet Propulsion Laboratory, Caltech, under a contract with NASA. We thank Nikko Hitech International Incorporated for supplying the YAlO3 substrates used in this work.|
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