En las fronteras de la Materia Condensada

Granular magnetic materials composed of nanocrystalline clusters of ferromagnetic elements embedded in a noble metal matrix have been extensively studied in the last years. In particular, it has been experimentally shown that the transport properties are very sensitive to the growth conditions. The physical reason underlying these effects are related to the shape and size of the clusters which depend strongly on the sample deposition way. In order to contribute to the comprehension of this effect, we calculate the electronic transport of multilayered granular alloys, composed of discontinuous Co layers embedded in Ag alternating with Ag layers. The electronic transport when the Co clusters percolate is also studied. We focus our attention on the two possible geometries of the conductivity: CIP (current parallel to the Co layers) and CPP (current perpendicular to the ones) and their dependence on the cluster's size. The electronic structure is selfconsistently calculated using a tight binding hamiltonian which includes a Hubbard term within the unrestricted Hartree Fock approximation. On the other hand, the conductivity tensor is obtained by using the semiclassical Boltzmann equation in the relaxation time approximation. We show that the conductivity decreases when the cluster's size becomes larger, but that it increases when the percolation situation is reached as it is experimentally observed.