Nonlinear current–voltage relations in polycrystalline perovskite manganites ceramics

Philip, John; Kutty, T. R. N.
July 2001
Applied Physics Letters;7/9/2001, Vol. 79 Issue 2
Academic Journal
Highly nonlinear current–voltage (J∝E[sup α]) relations with voltage-limiting characteristics are observed for Mg-doped lanthanum calcium manganite polycrystalline ceramics with nonlinearity coefficient, α=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 α increases on annealing at 1375 K in atmospheres of lower p[sub O[sub 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[sup 3+]/Mn[sup 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. © 2001 American Institute of Physics.


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