The grain size dependence of the resistance behaviors in doped lanthanum manganite polycrystalline films

Using the sol–gel spin-coating method, La0.67Sr0.33MnO3 and La0.7Ca0.3MnO3 polycrystalline films have been prepared. The polycrystalline films show much lower resistivity peak temperature Tp than that of the corresponding epitaxial film, and Tp shifts to higher temperature when the annealing temperature increases. The magnetization measurement reveals that all of the polycrystalline films have the same magnetic transition temperature as the corresponding epitaxial films. These results are different from the previous works. We ascribe the difference to the grain size of our polycrystalline samples being much smaller, so the conduction through the grain boundaries predominates over the intragrain conduction. In this case, spin disorder and magnetocrystalline anisotropy should be taken into account in explaining the magnetotransport behavior.