# Nonlinear current-voltage relations in polycrystalline perovskite manganites ceramics

Philip, John and Kutty, TRN (2001) Nonlinear current-voltage relations in polycrystalline perovskite manganites ceramics. In: Applied Physics Letters, 79 (2). pp. 209-211.

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Highly nonlinear current-voltage (J \propto E \alpha ) relations with voltage-limiting characteristics are observed for Mg-doped lanthanum calcium manganite polycrystalline ceramics with nonlinearity coefficient, \alpha = 2-9 at low-electric-field strengths of 2-5 V/mm, below magnetic transition temperatures. The current density increases with external magnetic field, so that magnetically tunable low-voltage varistors are realized. The increases on annealing at 1375 K in atmospheres of lower $\rho O_2$, and becomes more pronounced with decreasing grain size, indicating that nonlinear behavior is related to the outdiffusion of oxygen through the grain-boundary-layer regions. The increasing deficiency in $Mn^3^+ /Mn^4^+$ pairs reduces the hole-hopping probability leading to insulating barriers in the grain-boundary-layer regions. The barrier height is lowered by the external electric field, facilitating the charge-carrier movement between the grains. Since the conduction is due to spin-polarized tunneling, the external magnetic field increases the current.