Dielectric spectra in charge ordering state of Pr1-xCaxMnO3

We measured dielectric spectra in the charge ordering state of Pr1-xCaxMnO3 (0.30 less than or equal to x less than or equal to 0.50); for frequencies of 100 Hz similar to 15 MHz. Observed dielectric spectra were analyzed using the Debye model. The effective number of electrons (n/m) is nearly temperature independent. Dissipation, gamma, 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 similar or equal to 0.33. The gamma-value decreases in magnetic fields, hut does not scale with magnetization.