M. García-Hernández, A. de Andrés, J.L. Martínez, c. Prieto, A. Muñoz, L. Vázquez.

Instituto de Ciencia de materiales de Madrid. CSIC, Cantoblanco, E-28049.

The low temperature behaviour of the resistivity of pollycristalline thin films of magnetoresistive manganites has been investigated for grain sizes in the nanometric scale. For such a purpose, we have optimized the dc-sputtering deposition and annealing procedures so as to taylor the grain size of the deposits while keeping the basic features of the magnetic and transport properties of the bulk material. A sistematic upturn of the resistivity at around 50 K is observed in all films (12nm-80nm grain diameter). These results point out the existence of a Coulomb blockade mechanism affecting the conduction of electrons at least in the smallest grain sizes explored. The evolution of this effect with the magnetic field is also investigated.