Crossover between Kondo and electron–electron interaction effects in La0.75Sr0.20MnO3manganite 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 La 0.75 Sr 0.20 MnO 3 and La 0.75 Sr 0.20 Mn 1− c Co c O 3 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 T min , which in the Co-doped samples shifts towards higher temperatures as the Co concentration increases. T min varies approximately as c 1/3 . The application of an external magnetic field shows that the T min decreases linearly as the field increases, and above 0.7 T remains field independent. In magnetic fields, where T min is constant, T min varies as . For temperatures below T min the resistivity data can be fitted either with a or with a −ln T function, while for temperatures above the minimum the resistivity follows both a T 3 and a T 5/2 dependence. We believe that there is a crossover between a 'Kondo-like' scattering process and the 3D electron–electron interaction effects enhanced by disorder.