Colossal resistive relaxation effects in aPr0.67Ca0.33MnO3single 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, ${\mathrm{Pr}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_3.$ The metal-insulator transition is evidenced by an abrupt jump of the resistivity by several orders of magnitude at a well-defined time τ while there is no apparent singularity in the magnetization relaxation. This supports the view of a percolative behavior of current transport. The magnetic relaxation is discussed in terms of a two-level phenomenological model with a distribution of energy barriers.