Current-induced metallic behavior in Pr_0.5Ca_0.5MnO₃ thin films: competition between Joule heating and nonlinear conduction mechanisms

Abstract

Thin films of Pr_0.5Ca_0.5MnO₃ manganites exhibiting charge/orbital-ordered properties with colossal magnetoresistance have been synthesized by the pulsed laser deposition technique on both (100)-SrTiO₃ and (100)-LaAlO₃ substrates. The effects of current-induced metallic-behavior of the films are investigated as a function of the temperature and the magnetic field. Calculations based on a heat transfer model across the substrate, and our resistivity measurements reveal effects of Joule heating on charge transport over certain ranges of temperatures and magnetic fields. Our results also indicate that a nonlinear conduction, which cannot be explained by homogeneous Joule heating of the film, is observed when the material is less resistive (<10^-2 Ω .cm). The origin of this behavior is explained with a model based on local thermal instabilities associated with phase-separation mechanism and a change in the long range charge-ordered state.