Phase separation and 1/f noise in low-T-MI colossal magnetoresistance manganites

We report studies of the 1/f noise in La5/8-yPryCa3/8MnO3 (y = 0.3 - 0.4) which exhibits the metal-insulator transition (MIT) in zero magnetic field, and in Pr1-xCaxMnO3 (0.30.5), where the transition can be observed only in high magnetic field. Many-orders-of-magnitude noise enhancement at the MIT observed in both compounds indicates the generality of the percolation mechanism of the transition in these systems. Large discrete discontinuities of the resistivity-sw itching, which usually accompany the noise peak at the MIT-suggest that individual domains belonging to the percolation cluster undergo transitions back and forth between the metallic and insulating states. Signatures of metastability of the low temperature electronic state in these charge-ordered manganites and similarity of the switching dynamics with that of non-charge-ordered compounds indicate that the percolating phases in the studied systems are the ferromagnetic metallic and the metastable charge-disordered insulating phases.