Size effect of substitutional alkaline-earth elements on the electrical and structural properties of LaMnO3 films

Abstract

Tolerance factor controlled Mn-based colossal magnetoresistance (CMR) thin films (La0.7Ca0.3MnO3, La0.7Sr0.3MnO3, La0.7Sr(0.11)Ba(0.19)MnO(3), and La0.7Ca0.3MnO3) which have the same content of divalent cation and Mn3+/Mn4+ ratio were deposited on amorphous SiO2/Si substrate by rf magnetron sputtering at 350 degrees C substrate temperature. Post annealing treatment for I h at 600 degrees C was also carried out to investigate the effects of internal strain and chemical bonding nature from different divalent ions on the electrical properties of the films by maintaining a similar crystalline state. The films crystallized with pseudo cubic structure in spite of different tolerance factors. The sheet resistance of films changed according to crystallization and Mn-O bonding character. Mn L-edge X-ray absorption spectra revealed that Mn3+/Mn4+ ratio did not change in all the films and Mn 2p core level X-ray photoelectron spectra showed that Mn-O bonding property changed to more covalence as increasing tolerance factor by substitution with larger size divalent cation. O K-edge X-ray absorption spectra observed t(2g) and e(g) electron states and low resistivity after post anneal could be explained by the promotion of electrons to low binding energy state. Temperature coefficient of resistance (TCR) values were about -2.24 similar to -2.57%/K of as deposited CMR films and these values were reasonable for uncooled microbolometer applications. (C)2009 The Ceramic Society of Japan. All rights reserved.