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 tW annealed at 400 ° and evaluated tW dependence of thermal stability factor Δ, intrinsic critical current IC0 and damping constant α. It was found that spin-transfer torque efficiency (Δ /IC0) values increased with decreasing tW as compared with the same MTJ size D. α measured by ferromagnetic resonance increased with an increase in tW, which is consistent with those calculated from Δ /IC0. This result indicates that lower damping constant of MTJ with thin W insertion layer contributes to higher Δ /IC0.