Colossal resistive relaxation effects in a Pr0.67Ca0.33MnO3 single crystal

We report here on an experimental study of slow thermal relaxation effects from the metastable metallic-ferromagnetic phase to the insulating one in a charge-ordered manganese oxide, Pr0.6Ca0.33MnO3. The metal-insulator trans ition is evidenced by an abrupt jump of the resistivity by several orders o f magnitude at a well-defined time tau while there is no apparent singulari ty in the magnetization relaxation. This supports the view of a percolative behavior of current transport. The magnetic relaxation is discussed in ter ms of a two-level phenomenological model with a distribution of energy barr iers. [S0163-1829(99)00202-7].