Transport Properties of La 1-xSrxMnOz Thin Films in Oxygen Deficient and Excess States

Thin films of La1-x SrxMnOz (x=0.15 and 0.175) have been successfully fabricated by pulsed laser deposition. Resistivity and magnetoresistance of the films have been measured. With increasing post-annealing time or oxidizing gas pressure, the resistivity initially decreases and then increases. The latter increase has been observed for the first time in the present study. The observed initial reduction is attributed to the decrease in the oxygen deficiency of the as-grown film and the latter increase is attributed to the increase in cation vacancies. Semiconducting behavior of the sufficiently oxidized film is attributed to the localization of carriers due to the random potential produced by the cation vacancies. The resistivity enhancement in the oxygen excess state is found to increase the magnetoresistance ratio considerably.