Reduction in critical current density for spin torque transfer switching with composite free layer

A composite free layer (CFL) consisting of a soft layer and a hard layer exchange coupled in parallel is proposed. The experimental results showed that the critical current density (Jc) can be reduced from 7.05×106A∕cm2 of strong coupled CoFeB(12.5Å)∕Ru(4Å)∕NiFe(17.5Å) CFL to 2.65×106A∕cm2 of weak coupled CoFeB(12.5Å)∕Ru(15Å)∕NiFe(17.5Å) CFL. The macrospin simulations showed that the soft layer of CFL can assist the hard layer of CFL to switch at a lower Jc. These results suggest that by using CFL, it is possible to reduce the Jc of spin torque transfer switching without compromising the thermal stability.