Annealing induced grain growth and grain connectivity in an epitaxial film of La0.67Ca0.33MnO3 and its effect on low field colossal magnetoresistance

We have studied the effect of annealing on a strain-relaxed film of La0.67Ca0.33MnO3 (thickness 300 nm) grown epitaxially on SrTiO3, by using local probes like scanning tunneling microscopy and scanning tunneling potentiometry (STP) and bulk probes like resistivity and magnetoresistance. Annealing enhances the film resistivity near the peak and suppresses the peak temperature. We find that annealing leads to growth of large sized grains, but the larger grains have relatively high resistance grain boundary as seen by STP. This in turn enhances the low field MR of the annealed films.