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Crossover between Kondo and electron–electron interaction effects in La0.75Sr0.20MnO3 manganite doped with Co impurities?

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.