Dual referenced composite free layer design optimization for improving switching efficiency of spin-transfer torque RAM

We present a detailed numerical analysis of switching efficiency for the recently proposed dual referenced composite free layer structure with respect to Gilbert damping. Low anisotropy assistive layers enable reduction of Gilbert damping and an increase of partial spin polarization within those low anisotropy layers—not feasible with single layer structures that require high anisotropy for thermal stability. When the damping of the soft layers is ultra-low, an efficiency (kBT/μA) of 8.1 is achieved for the composite structure with perpendicular anisotropy. This represents an improvement of 286% and 913% relative to the state-of-the-art dual-referenced and conventional STT-RAM cells, respectively. Results for structures with longitudinal anisotropy are also presented. A linear calculation of the STT polarization pre-factor is also described that captures all reflections.