Magnetoresistance Enhancement in Mn$_{\rm x}$Ga$_{100 - {\rm x}}$/MgO/CoFeB Perpendicular Magnetic Tunnel Junctions by Using CoFeB Interlayer

Abstract

The magnetoresistance effects of the perpendicular magnetic tunnel junctions (p-MTJs) based on Mn-Ga ordered alloys are reported. By tuning the Mn-Ga composition, the MTJs based on and structured Mn-Ga alloys were achieved in the MTJ stack structure of Cr(40)/MnxGa100-x(30)/Mg(0.4)/MgO(2.2)/CoFeB(1.2)/Ta(5)/Ru(7) (nm). The values of magnetoresistance (MR) ratio at room temperature for different Mn-Ga composition are around 5%. In order to enhance the MR ratio, a thin CoFeB layer was introduced between the Mn-Ga and the MgO barrier. The MR effect shows a strong Mn-Ga composition dependent as CoFeB interlayer thickness increases. An MR ratio of 50% was obtained at room temperature when the CoFeB thickness is 1.5 nm for Mn0.2Ga38 based MTJs.