Current oscillation and low-field colossal magnetoresistance effect in phase-separated manganites

Current-induced switching from a metallic to an insulating state is observed in phase-separated states of (La1-yPry)(0.7)Ca0.3MnO3 (y=0.7) and Nd0.5Ca0.5Mn1-zCrzO3 (z=0.03) crystals. The application of magnetic fields to this current-induced insulating state causes a pronounced low-field negative magnetoresistance effect [rho(H)/rho(0)=10(-3) at H=1 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.