Ac and dc magnetotransport properties of the phase-separated La_0.6Y_0.1Ca_0.3MnO₃ manganite

The physical properties of the La_0.6Y_0.1Ca_0.3MnO₃ compound have been investigated, focusing on the magnetoresistance phenomenon studied by both dc and ac electrical transport measurements. X-ray diffraction and scanning electron microscopy analysis of ceramic samples prepared by the sol–gel method revealed that specimens are single phase and have average grain size of ∼0.5 μm. Magnetization and 4-probe dc electrical resistivity ρ(T,H) experiments showed that a ferromagnetic transition at T _C  ∼ 170 K is closely related to a metal-insulator (MI) transition occurring at essentially the same temperature T _MI . The magnetoresistance effect was found to be more pronounced at low applied fields (H ≤ 2.5 T) and temperatures close to the MI transition. The ac electrical transport was investigated by impedance spectroscopy Z(f,T,H) under applied magnetic field H up to 1 T. The Z(f,T,H) data exhibited two well-defined relaxation processes that exhibit different behaviors depending on the temperature and applied magnetic field. Pronounced effects were observed close to T _C and were associated with the coexistence of clusters with different electronic and magnetic properties. In addition, the appreciable decrease of the electrical permittivity ε′(T,H) is consistent with changes in the concentration of e _g mobile holes, a feature much more pronounced close to T _C .