OSCILLATIONS WITH CO AND CU THICKNESS OF THE CURRENT-PERPENDICULAR-TO-PLANE GIANT MAGNETORESISTANCE OF A CO CU/CO(001) TRILAYER/

The results of a rigorous quantum calculation of the current-perpendic ular-to-plane giant magnetoresistance (CPP GMR) of a Co/Cu/Co(001) tri layer without impurity scattering are reported. The conductances per s pin in the ferromagnetic (FM) and antiferromagnetic (AF) configuration s of the magnetic layers are computed from Kubo formula. The electroni c structure of the Cu and Co layers is described by fully realistic s, p,d tight-binding bands fitted to ab initio band structures of Cu and ferromagnetic fee Co. Depending on Co thickness, the CPP GMR ratio can be as high as 90%. The whole calculated effect is due solely to quant um reflections of electrons from perfectly fiat Co/Cu interfaces. The CPP GMR ratio is found to oscillate both with Co and Cu thickness, the respective oscillation amplitudes being 12 and 6% of the average GMR. The resistances in each spin channel per unit cross-sectional area of the trilayer range from 3 to 7 f Omega and oscillate with an amplitud e similar to 0.5 f Omega. An analytic asymptotic formula for resistanc e oscillations originating from the Cu Fermi surface is applied to ana lyze the numerical results. It is found that the resistance oscillatio ns for majority electrons in the FM configuration have periods dominat ed by the extremal radii of the Cu Fermi surface. These are the same p eriods as observed in the oscillatory exchange coupling. However, the amplitude of resistance oscillations with the Fermi-surface periods is negligibly small for the minority electrons in the FM configuration a nd for electrons of either spin orientation in the AF configuration. T he resistance oscillations of these electrons are dominated instead by periods determined by cutoffs of the conductance due to a mismatch be tween the Co and Cu bands across the Co/Cu interfaces.