Charge Separation and Pre-percolation Regime in Manganites

Complex manganites have been intensively studied in the last decade since they are model objects for investigations of the collosal magnetoresistance. Temperature dependence of La$_{0.875}$Sr$_{0.125}$MnO$_{3}$ single crystals' dielectric and magnetic properties are investigated in the wide range of temperature and external magnetic field. In order to clarify the nature of the charge, spin and orbital ordering as well as the nanoscale inhomogeneity dynamics, we studied their low-frequency capacitances. It is found that giant dielectric permittivity arises in this manganite. The origin of this enormous dielectric response is believed to be connected with the fact that in the pre-percolation regime of charge separation there are very thin regions of insulator phase with large net surface embedded in metallic matrix. The features of the temperature and field dependence of these dielectric properties are explained by the nanoscale dynamic inhomogeneties appearing due to charge and spin ordering.