EFFECT OF CRYSTALLINITY ON THE MAGNETORESISTANCE IN PEROVSKITE MANGANESE OXIDE THIN-FILMS

We report our study of the effect of crystallinity on the magnetoresis tance in epitaxial and polycrystalline La2/3Ba1/3MnO3 and La2/3Ca1/3Mn O3 thin films. Magnetoresistance in epitaxial films exhibits field dep endence and temperature dependence similar to bulk single crystals and sintered bulk ceramics. The polycrystalline films exhibit a markedly different behavior. The magnetoresistance in this case shows either a monotonic increase or saturation with decreasing temperature in contra st to that of epitaxial films in which the magnetoresistance peaks clo se to the ferromagnetic transition temperature. The field dependence i n the polycrystalline films is;also remarkably different. At low field s, we observe a sharp drop in resistance followed by a more gradual de crease at higher fields. Our data suggest that in addition to the intr insic magnetoresistance, grain-boundary transport contributes signific antly to the magnetoresistance in polycrystalline films. (C) 1997 Amer ican Institute of Physics.