Transport properties in manganite thin films

The resistivity of thin La(0.7)A(0.3)MnO(3) films (A = Ca, Sr) is investigated in a wide temperature range. The comparison of the resistivities is made among films grown by different techniques and on several. substrates allowing to analyze samples with different amounts of disorder. In the low-temperature nearly half-metallic ferromagnetic state the prominent contribution to the resistivity scales as T-alpha with a alpha similar or equal to 2.5 for intermediate strengths of disorder supporting the theoretical proposal of single magnon scattering in presence of minority spin states localized by the disorder. For large values of disorder the low-temperature behavior of the resistivity is well described by the law T-3 characteristic of anomalous single magnon scattering processes, while in the regime of low disorder the alpha exponent tends to a value near 2. In the high temperature insulating paramagnetic phase the resistivity shows the activated behavior characteristic of polaronic carriers. Finally in the whole range of temperatures the experimental data are found to be consistent with a phase separation scenario also in films doped with strontium (A = Sr).