Asymmetric magnetization reversal of the Heusler alloy Co2FeSi as free layer in an CoFeB/MgO/Co2FeSi magnetic tunnel junction

Abstract

We report the in-plane magnetization reversal behavior of the Co2FeSi Heusler alloy free layer in a bottom-pinned magnetic tunnel junction film with 149% TMR. Using magneto-optic indicator film imaging, we visualize the magnetic domain dynamics of this buried layer integrated within a full magnetic tunnel junction stack. The magnetic domain dynamics reveal anisotropic magnetization reversal within Co2FeSi under applied in-plane magnetic fields. While the reversal behavior under in-plane fields applied perpendicular to the in-plane exchange bias direction indicates smooth, coherent rotation away from the easy axis, asymmetric magnetic reversal behavior is observed along the easy axis. Reversed domains propagate from the interior of the film laterally outward toward the edges as the free layer magnetization switches into parallel alignment with the pinned synthetic antiferromagnetic reference layer (IrMn/CoFe/Ru/CoFeB). On the other hand, domains propagate from the film edges inward for the free layer transition into antiparallel alignment with the reference layer. These results have important implications for Heusler magnetic tunnel junction device performance.