TRANSPORT-PROPERTIES OF CO-NI SUPERLATTICES

We calculate the ballistic conductance G and the diffusive conductivit y sigma for Co-Ni superlattices grown in the (111) direction, with the intention of investigating the effect of the superlattice band struct ure on the electric transport properties. The calculation is carried o ut as a function of the number of atomic layers of each material, in t he framework of the semiclassical approximation (Boltzmann's equation) and assuming that each spin component contributes independently. A Hu bbard tight-binding Hamiltonian, solved in the unrestricted Hartree-Fo ck approximation and parametrized to fit bulk equilibrium values, is u sed to obtain the band structure in each case. We find that the presen ce of interfaces reduces the in plane and, more strongly, the perpendi cular to the plane electric conduction, even when impurity scattering is disregarded. The results for G and sigma show qualitative differenc es and thus, in the interpretation of the experiments, it is important to ascertain the precise nature of the transport regime. We do not fi nd the oscillatory behavior of the conductivity as a function of the n umber of layers, found in recently reported experimental results. This certainly is not a matter of accuracy of the calculations and therefo re rules out the hypothesis that the oscillatory behavior is due to si mple band structure effects.