GRAIN-BOUNDARY EFFECTS ON THE MAGNETORESISTANCE PROPERTIES OF PEROVSKITE MANGANITE FILMS

The role of grain boundaries in the magnetoresistance (MR) properties of the manganites has been investigated by comparing the properties of epitaxial and polycrystalline films of La0.67D0.33MnO3-delta (D = Ca, Sr, or vacancies). While the MR in the epitaxial films is strongly pe aked near the ferromagnetic transition temperature and is very small a t low temperatures, the polycrystalline films show large MR over a wid e temperature range down to 5 K. The results are explained in terms of switching of magnetic domains in the grains and disorder-induced cant ing of Mn spins in the grain-boundary region.