Perpendicular giant magnetoresistance and magnetic switching properties of a single spin valve with a synthetic antiferromagnet as a free layer

We study the current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) and magnetic switching behavior of single spin-valve (SV) films with two different free layers—one is a single ferromagnet (FM) layer, while the other is a synthetic antiferromagnet (SyAF) consisting of ${\mathrm{Co}}_{90}{\mathrm{Fe}}_{10}/{\mathrm{R}\mathrm{u}/\mathrm{C}\mathrm{o}}_{90}{\mathrm{Fe}}_{10}.$ When the interlayer Cu thickness is 2.5 nm, the SyAF as a free layer greatly enhances the CPP-GMR of SVs from 0.8% to 3.6%. The GMR enhancement effect decreases with increasing interlayer Cu thickness. We argue that the MR enhancement by the SyAF is probably because of strong reflection of the majority spins by the interface between ${\mathrm{Co}}_{90}{\mathrm{Fe}}_{10}$ and ruthenium. Experimental and theoretical studies of the magnetic switching behavior show that the SVs with SyAF have a much better tendency to form a single magnetic domain than the conventional ones. The single domain structure results in a size-independent magnetic switching field of the SVs with SyAF at the low aspect ratio 1.