CHARACTERIZATION OF FILMS OF LA1-XSRXMNO3-DELTA GROWN BY MEANS OF METAL-ORGANIC CHEMICAL-VAPOR-DEPOSITION

An effort to develop La manganites for possible sensor applications ha s led to the successful growth of La1-xBxMnO3-delta (B = Sr, Ca) thin films on single crystal MgO, Al2O3, and LaAlO3 substrates. Here we con centrate on Sr-doped material on LaAlO3 with Curie temperature T-c = 2 62 +/- 2 K. T-c was determined from magnetization measurements using A rrott plots, and agrees well with the observed resistivity peak in zer o applied magnetic field (H). This T-c corresponds closely to a Sr con tent x = 0.17 reported in bulk materials. At H = 60 kOe the maximum ma gnetoresistance Delta rho/rho approximate to 0.95. No discernible hyst eresis, as might be expected for structural phase transitions, was obs erved. When plotted as a function of reduced temperature T/T-c, the ma gnetization extrapolated to zero H is best fit by a Brillouin function with an effective spin value [S] much larger than the [S] = 1.9 indic ated by the composition. This may be indicative of magnetic polaron fo rmation, especially near the magnetic and transport transition tempera tures. At temperatures far below T-c there is an increase in resistivi ty of the thin films, which is considerably modified by the applicatio n of a field of 50 kOe. The conductivity, however, remains finite as t he temperature approaches zero, indicating transport in states close t o but above the mobility edge. (C) 1997 American Institute of Physics.