INFLUENCE OF STRAIN AND MICROSTRUCTURE ON MAGNETOTRANSPORT IN LA0.7CA0.3MNO3 THIN-FILMS

A La0.7Ca0.3MnO3 thin film made by pulsed laser deposition (PLD) and a nother film of the same composition made by metal organic chemical vap or deposition (MOCVD), both on single crystal LaAlO3, were subject to a series of six, short, controlled anneals. The oxygen content was pur posely not changed in the films from the first anneal to subsequent an neals. After each anneal, the film microstructures were characterized to determine average grain size, lattice constants, nonuniform strain, and crystalline mosaic spread, and these parameters were correlated w ith the magnetotransport properties. For both sets of films, the influ ence of annealing was to both increase the temperature at which the ma ximum in the magnetoresistance occurs (T-m) and the maximum magnetores istance (MR) value. The improvement in film properties occurred in con junction with stress relaxation and improved crystallinity, as a resul t of grain growth. The MOCVD films showed poorer grain coupling and po orer epitaxy compared to the PLD films. These features did not signifi cantly influence the absolute values of the resistivity, but did produ ce spin canting in the MOCVD film, as seen in magnetization and resist ivity versus field data. The canting resulted in a lower T-m and depre ssed MR value for the MOCVD film which increased only marginally with annealing. The work highlights the importance of controlling microstru cture for optimizing properties of colossal magnetoresistance films. ( C) 1998 American Institute of Physics. [S0021-8979(98)05818-6].