Current Oscillation and Low-Field Colossal Magnetoresistance Effect in Phase-Separated Manganites

Abstract

Current-induced switching from a metallic to an insulating state is observed in phase-separated states of $({\mathrm{La}}_{1\ensuremath{-}y}{\mathrm{Pr}}_{y}{)}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$ ($y=0.7$) and ${\mathrm{Nd}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{Mn}}_{1\ensuremath{-}z}{\mathrm{Cr}}_{z}{\mathrm{O}}_{3}$ ($z=0.03$) crystals. The application of magnetic fields to this current-induced insulating state causes a pronounced low-field negative magnetoresistance effect [$\ensuremath{\rho}(H)/\ensuremath{\rho}(0)={10}^{\ensuremath{-}3}$ at $H=1\text{ }\text{ }\mathrm{kOe}$]. The application of a constant voltage also causes the breakdown of the Ohmic relation above a threshold voltage. At voltages higher than this threshold value, oscillations in currents are observed. This oscillation is well reproduced by a simple model of local switching of a percolative conduction path.