Processing Magnetoresistive Thin Films Via Chemical Solution Deposition
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Processing magnetoresistive thin films via chemical solution deposition A. D. Pollia) and F. F. Lange Materials Department, Materials Research Laboratory, University of California, Santa Barbara, California 93106
M. Ahlskogb) and Reghu Menonc) Institute for Polymers and Organic Solids, University of California, Santa Barbara, California 93106
A. K. Cheetham Materials Department, Materials Research Laboratory, University of California, Santa Barbara, California 93106 (Received 4 August 1997; accepted 5 October 1998)
A chemical solution deposition (CSD) procedure was used to prepare epitaxial lanthanum calcium manganese oxide (LCMO) thin films on (100) SrTiO3 single-crystal substrates. The colossal magnetoresistance (CMR) properties of the films were found to be comparable to those processed with vacuum deposition techniques and to bulk samples. The (200) LCMO d-spacing and insulator-metal transition temperature sTIM d were measured for films heat-treated at different temperatures, partial pressures of O2 , and different times. The variations observed suggest a direct link between lattice parameter and TIM , as can be understood through their mutual dependence on the Mn41yMn31 ratio. The measurements also suggest that film and powder samples crystallize Mn41 -rich with respect to the Ca-substitution level, consistent with the larger lattice parameter and higher TIM observed following short heat treatments at high temperatures or long treatments at lower temperatures. Films refired in reducing conditions had the largest (200) d-spacing and slightly lower TIM , as expected from the 30% Ca-substitution level and consistent with the LCMO electronic/magnetic phase diagram constructed for bulk samples.
I. INTRODUCTION
Since the rediscovery1 in 1993 of large negative magnetoresistance in the manganate-based perovskites, much effort has been directed at understanding the physics and chemistry of the colossal magnetoresistance (CMR) phenomenon. In contrast, the present research paper will address several thin film processing issues, with emphasis on understanding the factors concerning reliable reproduction of CMR properties. Pure LaMnO3 (LMO) is an orthorhombically distorted perovskite at room temperature. When LMO is stoichiometric, charge balancing requires all of the manganese ions to carry a valence of 31. When Ca21 is substituted for La31 , an identical fraction of Mn31 must be oxidized to Mn41 in order to maintain charge balance within a nondefective structure. Along with a variation in the Mn41yMn31 ratio, substitution of Ca21 for La31 changes the room temperature structural distortion of the a)
Current address: Max-Planck-Institut f¨ur Metallforschung, Stuttgart, Germany. b) Current address: Katholieke Universiteit Leuven, Laboratorium voor Vaste Stoffysica en Magnetisme, B-3001 Leuven, Belgium. c) Current address: EMRI-Molecular Sciences, University of California – Los Angeles, Los Angeles, California. J. Mater. Res., Vol. 14, No. 4, Apr 1999
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