Influence of synthetic antiferromagnet free layer on current-perpendicular-to-plane spin-valves

We study current-perpendicular-to-plane (CPP) geometrical giant magnetoresistance (GMR) and magnetic switching property for single spin-valves (SVs). Applying a synthetic antiferromagnet (SyAF) instead of a single ferromagnet film as a free layer, the resistance-change area product ΔRA of the SVs is strongly enhanced from ∼ 1.84 mΩ μm² to ∼ 16.8 mΩ μm² and the CPP-GMR ratio changes from 0.8% to 3.6%. The study of the magnetic switching behavior by both experiment and single-domain thermal activation modeling shows that the SVs with SyAF as a free layer approaches a single-domain magnet even with a low aspect ratio 1 as long as its size diminishes to ∼0.18 μm². Because of the single-domain structure, the SVs with SyAF give a size-independent magnetic switching field when the aspect ratio is 1.