Electrical transport properties of LaNi_1-xM_xO₃ (M = Co, Mn) thin films fabricated by pulsed laser deposition

Abstract

Highly oriented thin films of LaNi_1-xM_xO₃ (M = Mn, Co) are grown on LaAlO₃(100) substrate by pulsed laser deposition. They undergo a metal to insulator transition when the Mn or Co concentration is increased. The observed conduction pattern is highly sensitive to the doping concentration in these thin films. The conduction pattern also varies as the doping element is varied from Mn to Co. There is a large dominance of electron-lattice interactions in the conduction mechanism of the charge carriers. While the metallic thin films of LaNi_1-xCo_xO₃ show a linear variation of resistivity with temperature, LaNi_1-xMn_xO₃ thin films exhibit a prominent square-root dependence of resistivity on temperature. At high concentrations of Mn or Co, the conduction takes place via a polaron hopping mechanism, which suggests that lattice polarization may be present in these films. The change observed in the transport properties is attributed to the charge disproportionation between the Ni³⁺-Ni²⁺ pairs, which are favoured more in Mn doped thin films. The photoelectron spectroscopic studies give evidence of charge disproportionation present in these films.