Annealing effect on transport properties of Nd0.67Sr0.33MnO3 thin films

Annealing dependence of the lattice parameter, resistivity, magnetoresistan ce and thermopower have been studied on Nd0.87Sr0.33MnO3 thin films deposit ed on LaAlO3 and alumina substrates by pulsed laser ablation. Upon annealin g at 800 degrees C and 1000 degrees C the lattice constant of the LaAlO3 fi lm tends toward that of the bulk target due to reduction in oxygen vacancie s. This results in a metal-insulator transition at temperatures which incre ase with progressive annealing along with a decrease in the observed low te mperature MR. Using a magnon scattering model we estimate the e(g) bandwidt h of the film annealed at 1000 degrees C and show that the magnon contribut ion to the resistivity is suppressed in a highly oxygen deficient film and gains prominence only upon subsequent annealing. We also show that upon ann ealing, the polaron concentration and the spin cluster size increases in th e paramagnetic phase, using an adiabatic polaron hopping model which takes into account an exchange dependent activation energy above the resistivity peak.