Mean free path effects on the current perpendicular to the plane magnetoresistance of magnetic multilayers

We have carried out an experimental and theoretical study of the magnetores istance MR(H) in the CPP (current perpendicular to the planes) mode for two types of magnetic multilayers that differ only in the ordering of the magn etic layers: [Co(10 Angstrom)/Cu(200 Angstrom)/Co(60 Angstrom)/Cu(200 Angst rom)](N) and [Co(10 Angstrom)lCu(200 Angstrom)](N)[Co(60 Angstrom)/Cu(200 A ngstrom)]N. The series resistor model predicts that in the;CPP mode MR(H) i s independent of the ordering of the layers. Nevertheless, the measured MR( H) curves were found to be completely different for the two cases. Calculat ions based on a realistic band structure and the Kubo formula show that the results are a consequence of a long mean free path.