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

Abstract

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× 106 A cm2 of strong coupled CoFeB (12.5 Å) Ru (4 Å) NiFe (17.5 Å) CFL to 2.65× 106 A cm2 of weak coupled CoFeB (12.5 Å) Ru (15 Å) NiFe (17.5 Å) 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. © 2008 American Institute of Physics.