Dielectric Spectra in Charge Ordering State of Pr1-xCaxMnO3

We measured dielectric spectra in the charge ordering state of Pr 1- x Ca x MnO 3 (0.30 ≤ x ≤0.50), for frequencies of 100 Hz∼15 MHz. Observed dielectric spectra were analyzed using the Debye model. The effective number of electrons ( n / m ) is nearly temperature independent. Dissipation, γ, drastically increases with cooling. Temperature dependence is almost the same as resistivity curve. This indicates that the hopping of polarons dominate both dc- and ac-electrical transport in the charge ordering phase. Based on the small-polaron-hopping model, x -dependent activation energy is estimated, which reaches a maximum at x ≃0.33. The γ-value decreases in magnetic fields, but does not scale with magnetization.