Andreev reflection measurements of spin polarization

We discuss aspects of Andreev reflection AR measurements in normal metal-superconductor N-S and ferromagnet-superconductor F-S devices. We describe the analytical model used to quantify spin polarization from the conductance measurements and discuss the validity of this simple model using parabolic bands as simple surrogates for real band structures. We present AR measurements of spin polarization in a Cu-Pt-Pb and Co-Pt-Pb lithographically fabricated nanocontact systems where a scattering layer of has been deliberately added to the interface to enable the study of the effect of pair-breaking scattering on AR conductance and spin polarization. We compare these results to the previously published results from clean Cu-Pb and Co-Pb devices and argue that the measurements in devices with the Pt layer can be explained by the presence of inelasticscattering-induced pair-breaking effects. We modify the analytical model to include this effect and show that in some instances, it may be impossible to distinguish between the effects of a finite spin polarization and inelastic scattering. This has implications for AR measurements of spin polarization at disordered or poorly formed F-S interfaces.