The low-temperature specific heat and electrical resistivity of the polycrystalline non-stoichiometric manganites La 0.95−x Sr x MnO 3 have been investigated in the doping region x = 0.00-0.30. The specific heat has terms proportional to T and T 3 . The resistivity of the samples decreases as T 1/2 with increasing temperature, goes through a minimum and then increases proportionally to T 3 . The temperature T min , corresponding to the minimum of the resistivity, shifts with Sr content as T min ∼ x −2/5 .

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The transverse magnetoresistance of disordered Zr 1Ϫx Rh x thin films has been measured above the superconducting transition temperature T c as a function of temperature in a magnetic field up to 60 kG. The investigated films are disordered enough to indicate quantum corrections due to localization and electronelectron interaction effects. The field and temperature dependence of the observed magnetoresistance is interpreted in terms of weak-localization, Aslamazov-Larkin, and Maki-Thompson superconducting fluctuations effects. From the comparison of the experimental results with theoretical calculations, the electron-electron attraction strength, ␤(T/T c ), is derived and is in good agreement with Larkin's theory. The total phasebreaking rate Ϫ1 has been estimated and ascribed to electron-phonon, electron-electron, electron-fluctuation, and spin-flip scattering mechanisms. ͓S0163-1829͑97͒00934-X͔

The resistivity minimum in manganites is still under debate. Recent publications discussed two possible scenarios: (i) electron–electron interaction in weak disordered systems and (ii) charge carriers tunnelling between antiferromagnetic coupled grains. In order to resolve this puzzle, we present a systematic study on the electrical resistivity, ρ(T), which was carried out in ceramic samples of La0.75Sr0.20MnO3 and La0.75Sr0.20Mn1−cCocO3 manganites over the temperature ranges 0.4–60 K and 4–60 K respectively. All compounds show a minimum in the resistivity at a characteristic temperature Tmin, which in the Co-doped samples shifts towards higher temperatures as the Co concentration increases. Tmin varies approximately as c1/3. The application of an external magnetic field shows that the Tmin decreases linearly as the field increases, and above 0.7 T remains field independent. In magnetic fields, where Tmin is constant, Tmin varies as . For temperatures below Tmin the resistivity data can be fitted either with a or with a −lnT function, while for temperatures above the minimum the resistivity follows both a T3 and a T5/2 dependence. We believe that there is a crossover between a ‘Kondo-like’ scattering process and the 3D electron–electron interaction effects enhanced by disorder.

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