Electronic scattering from Co/Cu interfaces:: In situ measurement, comparison with microstructure, and failure of semiclassical free-electron models

We show that novel thickness-dependent film conductance measurements, taken in situ during deposition of NiO/Co/Cu/Co spin valves and compared with thickness-dependent microstructural characterization, indicate a qualitative failure of widely accepted semiclassical free-electron models of giant magnetoresistance (GMR). Both in situ Auger electron spectroscopy covering experiments and ex situ x-ray diffraction measurements of peak intensity for Co/Cu/Co films indicate that the defect concentration does not vary noticeably as a function of thickness. The microstructural measurements suggest that the bulk scattering parameters rho and lambda should be considered to be constant within each layer, and that the surface scattering parameter p does not change between layers. Under these constraints, it becomes difficult to fit even qualitatively the highly asymmetric scattering behavior measured during the formation of Co/Cu vs Cu/Co interfaces. Calculations incorporating realistic band structure resolve the observed inconsistency between free-electron model calculations and experiment. The asymmetry in scattering is understood here to arise simply from the higher density of unfilled d states in Co compared with Cu. (C) 2000 American Institute of Physics. [S0021-8979(00)72308-5].