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 has led to the successful growth of La1-xBxMnO3-delta (B = Sr, Ca) thin films on single crystal MgO, Al2O3, and LaAlO3 substrates. Here we concentrate on Sr-doped material on LaAlO3 with Curie temperature T-c = 262 +/- 2 K. T-c was determined from magnetization measurements using Arrott plots, and agrees well with the observed resistivity peak in zero applied magnetic field (H). This T-c corresponds closely to a Sr content x = 0.17 reported in bulk materials. At H = 60 kOe the maximum magnetoresistance Delta rho/rho approximate to 0.95. No discernible hysteresis, as might be expected for structural phase transitions, was observed. When plotted as a function of reduced temperature T/T-c, the magnetization extrapolated to zero H is best fit by a Brillouin function with an effective spin value [S] much larger than the [S] = 1.9 indicated by the composition. This may be indicative of magnetic polaron formation, especially near the magnetic and transport transition temperatures. At temperatures far below T-c there is an increase in resistivity of the thin films, which is considerably modified by the application of a field of 50 kOe. The conductivity, however, remains finite as the temperature approaches zero, indicating transport in states close to but above the mobility edge. (C) 1997 American Institute of Physics.