  We examine transport properties of a magnetic superlattice with current
perpendicular to the planes. In the limit that the phase-breaking and spin flip
scattering lengths are greater than the system size, a multiple-scattering
approach is used to calculate the 4-probe conductance. We show that by tuning
the strength of tunnel barriers placed between the current and voltage probes
giant magnetoresistance ratios of arbitrary strength and size are achievable.
