Tunnel magnetoresistance and spin-transfer-torque switching in polycrystalline Co2FeAl full-Heusler alloy magnetic tunnel junctions on Si/SiO2 amorphous substrates

摘要

We studied polycrystalline B2-type Co2FeAl (CFA) full-Heusler alloy basedmagnetic tunnel junctions (MTJs) fabricated on a Si/SiO2 amorphous substrate.Polycrystalline CFA films with a (001) orientation, a high B2 ordering, and aflat surface were achieved using a MgO buffer layer. A tunnel magnetoresistance(TMR) ratio up to 175% was obtained for an MTJ with a CFA/MgO/CoFe structure ona 7.5-nm-thick MgO buffer. Spin-transfer torque induced magnetization switchingwas achieved in the MTJs with a 2-nm-thick polycrystalline CFA film as aswitching layer. Using a thermal activation model, the intrinsic criticalcurrent density (Jc0) was determined to be 8.2 x 10^6 A/cm^2, which is lowerthan 2.9 x 10^7 A/cm^2, the value for epitaxial CFA-MTJs [Appl. Phys. Lett.100, 182403 (2012)]. We found that the Gilbert damping constant evaluated usingferromagnetic resonance measurements for the polycrystalline CFA film was~0.015 and was almost independent of the CFA thickness (2~18 nm). The low Jc0for the polycrystalline MTJ was mainly attributed to the low damping of the CFAlayer compared with the value in the epitaxial one (~0.04).