Insertion Layer Thickness Dependence of Magnetic and Electrical Properties for Double-CoFeB/MgO-Interface Magnetic Tunnel Junctions

We have studied the magnetic and electrical properties of double CoFeB-MgO interface magnetic tunnel junctions (MTJs) with various W insertion layer thicknesses t
_W
annealed at 400 °C and evaluated t
_W
dependence of thermal stability factor Δ, intrinsic critical current I
_C0
and damping constant α. It was found that spin-transfer torque efficiency (Δ/I
_C0
) values increased with decreasing t
_W
as compared with the same MTJ size D. α measured by ferromagnetic resonance increased with an increase in t
_W
, which is consistent with those calculated from Δ/I
_C0
. This result indicates that lower damping constant of MTJ with thin W insertion layer contributes to higher Δ/I
_C0
.