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Current-perpendicular-to-plane (CPP) geometrical giant magnetoresistance (GMR) single spin-valve (SPV) structures with synthetic antiferromagnets (SyAFs) as free layers were fabricated. The sample sizes range from micron to submicron. We demonstrate that SyAFs as free layers dramatically enhances the CPP-GMR ratio from 0.83% to 3.56% at room temperature and also double the resistance-area product in single SPV films. A study of the magnetic switching behavior by both experiment and single-domain thermal activation modeling shows that the CPP-GMR SPV with SyAF structure approaches that of a single-domain magnet even with low aspect ratio of 1 as long as its size diminishes to ∼0.18 μm2. The single-domain structure brings size-independent magnetic switching field when the aspect ratio is 1. The large GMR ratio at room temperature, single-domain structure and size-independent magnetic switching field demonstrate the great potential of CPP-GMR SPVs with SyAF free layers for use in future ultrahigh density magnetic storage devices. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]