Impedance spectroscopy evidence of the phase separation in La0.3Pr0.4Ca0.3MnO3 manganite

We have measured electrical resistance R(T), magnetization M(T), and for the first time impedance spectroscopy Z(T,ω) of polycrystalline samples of La0.3Pr0.4Ca0.3MnO3 compounds. The combined results suggest the coexistence of two metallic ferromagnetic phases below the Curie temperature of the system. The R(T) data exhibit two important features: the occurrence of a metal - insulator (MI) transition at temperatures close to TMI∼170K and a large thermal hysteresis below TMI. The first feature was found to be associated with the development of ferromagnetism and takes place when the magnetization of the samples becomes about 15% of its saturated value at low temperatures. The second feature suggests two contributions to R(T) below the Curie temperature TC. The Z(T,ω) data taken from 77 to 300 K and frequency varying from 5 to 107Hz are much more valuable. These results reveal two well defined bulk contributions to the transport properties of these manganites below ∼170 K: one occurring at high frequencies ∼4 x 106Hz and a second one at low frequencies, typically on the order of 1.5x105Hz. An analysis of the Z(T,ω) data suggests that these contributions are related to the spin lattice relaxation rate of the two distinct phases. Such a result suggests a phase separation below TC in the compound in complete agreement with recent muon spin relaxation and neutron spin echo measurements performed on manganites. [copyright] 2001 American Institute of Physics