PERPENDICULAR MAGNETORESISTANCE IN MAGNETIC MULTILAYERS - THEORETICAL-MODEL AND DISCUSSION

After a general introduction describing the mechanisms of the current perpendicular to the layer plane magnetoresistance (CPP-MR), a microscopic model based on the Boltzmann equation is presented and a general expression of the magnetoresistance is derived in which the spin diffusion length appears as the unique scaling length of the problem. In the limit where the spin diffusion lengths are much larger than the layer thicknesses, the expression of the CPP-MR becomes very simple and similar to that already used at Michigan State University for the analysis of experimental results. Out of this limit, the model predicts a dramatic reduction of the CPP-MR if the spin diffusion lengths are shortened sufficiently by paramagnetic impurities or spin-orbit scatterers. Finally, a calculation is presented of the spin-dependent interface resistances involved in the model and related to interface potential steps, and experimental data are compared.