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 $\alpha \simeq 2.5$
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 ($A=Sr$).Comment: 5 figure
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