Structural,Electronic And Magnetic Properties Of Mn_xGa/Co₂MnSi?x=1,3? Bilayers

The novel spin transfer torque magnetic random access memory for embedded memory combining the advantages of high recording density,high speed performance and low energy consumption.It is expected to completely replace the traditional magnetic storage device.MnGa alloys are an ideal electrode material for making novel spin random magnetic memory devices.The tetragonal MnGa alloy meets the requirement of stability for magnetic tunnel junctions due to the large perpendicular magnetic anisotropy.With low saturation magnetization,MnGa alloys are suitable for the free layers in magnetic tunnel junctions.The high spin polarizability of MnGa alloys provides a prerequisite for making magnetic tunnel junctions with a high tunnel magnetoresistance.The ultralow damping constant of MnGa alloy supports low power current-induce switching,and it is a key factor to achieve low power consumption.In addition,MnGa alloys are appropriate for high thermal stability since their high Curie temperature.However,the investigations on MnGa/MgO/MnGa perpendicular magnetic tunnel junction show its tunnel magnetoresistance is serious low.One reason is a large lattice mismatch between MnGa electrode and MgO barrier layer;another is that the interfacial diffusion of Mn atoms may bring magnetic impurities into MgO barrier.In order to solve the lattice mismatch and interfacial diffusion,large cubic Co-based Heusler alloys were formed as interlayer because the structure of MnGa alloys derive from Heusler.Co₂MnSi is a promising candidate interlayer due to the strong interfacial antiferromagnetic exchange coupling between MnGa and Co₂MnSi.The half-metallicity of Co₂MnSi can lead to a high magnetoresistance at room temperature.Co₂MnSi has a high Curie temperature and low damping constant,which guarantees high thermal stability and low power consumption.Moreover,the Co₂MnSi as a soft magnetic film is sensitive to the magnetic moment of the MnGa electrode.Finally,the MnGa/Co₂MnSi bilayer composite electrode not only alleviates the lattice mismatch but also overcomes the interfacial diffusion of Mn atoms.The key of research is the interfacial exchange coupling between the MnGa alloy and Co₂MnSi interlayer.The structure stability,electronic and magnetic properties of D0₂₂-and L1₀-MnGa/Co₂MnSi bilayers were studied by performing first-principles calculations based on density functional theory.The calculation results of the thermodynamic stability of MnGa/Co₂MnSi bilayers show that the interface configuration is likely the MM-MS_B model with antiferromagnetic exchange coupling in interface.The atom magnetic moments near the MnGa and Co₂MnSi interface are enhanced by strong antiferromagnetic exchange coupling.The electronic structure of interface reveal the Co₂MnSi embedded layer enhances the spin polarizability of MnGa electrode.Finally,there is contact potential difference between the MnGa electrode and the Co₂MnSi layer.The built-in electric field in the interface region leads to the charge migrate from the MnGa to the Co₂MnSi.In summary,the Co₂MnSi film plays a role of a spin-polarizer in enhancing the spin polarizability of the MnGa electrode.This research elucidates the electronic structure and magnetic behavior in MnGa/Co₂MnSi interface.A reasonable explanation is given for the interfacial exchange coupling mechanism between the MnGa thin-film and the Co₂MnSi interlayer.We propose a new scheme that a spin-polarizer is embedded in the spin device to increase spin polarizability of the electric current.We believe that this scheme has very important guiding significance for the design and research of spin devices.