Correlation between extrinsic magnetoresistance and electroresistance in La0.6Pb0.4MnO3 thin films as revealed from current-voltage and ferromagnetic resonance studies

We have investigated magnetoresistance (MR) and electroresistance (ER) of well characterized La_0.6Pb_0.4MnO₃ (LPMO) films having two different crystallinity (i) (00l) oriented single-crystalline, SC, i.e. without any grain boundaries, and (ii) nanocrystalline, NC, with an average grain size of 17 nm. Both MR and ER were remarkably different for the two films, that is, (i) NC films exhibited a highest MR of ∼100% near the metal-insulator transition temperature; while for SC films the MR was in the range of 40-60%, (ii) NC films exhibited a finite ER, which increased monotonically with decreasing temperature; while in SC films ER was completely absent. Using current-voltage characteristic and ferromagnetic resonance studies we demonstrate that both enhanced MR and ER in NC films are extrinsic in nature and originate due to the presence of spin glassy grain boundaries.