Self-doped lanthanum manganites as a phase-separated system: Transformation of magnetic, resonance, and transport properties with doping and hydrostatic compression

The magnetic, resonance, and electric properties of LaxMnO3+delta (0.815 <= x <= 1.0) polycrystalline samples have been studied in the temperature range of 77-370 K and at high pressures of up to 11.5 kbar. It is shown that the increase in the La/Mn ratio gives rise to a change in the low temperature magnetic state from ferromagnetic to cluster spin glass, as well as to a drastic transformation of electric properties. A peculiar double-peaked shape is characteristic of the resistivity versus temperature curves for the intermediate range of x values. Within this range, the application of high pressures drastically changes both the value of resistivity and the character of its temperature dependence. It is shown that the approach, which regards the state of LaxMnO3+delta polycrystals as a mixture of interpenetrating paramagnetic insulating and ferromagnetic metallic phases, is able to successfully describe the peculiarities of the temperature dependence of total resistivity, as well as the features of its transformation under hydrostatic compression. It is demonstrated that the formation of a low temperature resistance peak is a result of a wide-temperature-region coexistence of the phases, which exhibits opposite trends in the temperature dependences of resistivity. The conclusion is made that not only does hydrostatic compression result in drastic changes in the relative volume fractions of the coexisting phases, but it also affects the intrinsic parameters of each of the phases. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3007993]