Distinctive current-induced magnetization switching in a current-perpendicular-to-plane giant-magnetoresistance nanopillar with a synthetic antiferromagnet free layer

We investigated current-induced magnetization switching (CIMS) in two types of pseudo-spin-valve nanopillars with current-perpendicular-to-plane giant magnetoresistance (CPP-GMR); Co90Fe10(10nm)∕Cu(10nm)∕Co90Fe10(2.5nm) (conventional type) and Co90Fe10(10nm)∕Cu(10nm)∕Co90Fe10(1.5nm)∕Ru(0.45nm)∕Co90Fe10(2.5nm) (synthetic antiferromagnet; SyAF type). We observed the CIMS in the both CPP-GMR structures at room temperature. In particular for the SyAF type nanopillars, the CIMS was observed only in a negative current regime. We also discovered that the applied magnetic field dependence of the CIMS shows absolutely different behavior from that of the conventional type. These peculiar CIMS behaviors with the SyAF free layer are attributed to majority electron spin transfer torque from the thick to the thin Co90Fe10 layers, enhanced by the presence of a Ru layer.