The paper was published in ACS Applied Materials & Interfaces.
In spite of considerable progress in the last decades, ultra-thin oxide (MgO and Al2O3) spacers serving as tunnel barriers provided no sufficient magnetoresistance (MR) value in vertical spin-valve. Recently, 2D materials displaying extremely large diversity of electronic and structural properties became under consideration as alternative spacer materials. Graphene and h-BN were considered as low-resistance barriers for a vertical spin-valve. Additionally to them, usage of the transition metal dichalcogenides (TMDs) can significantly expand the variety of electronic properties and tune the effectiveness of magnetic junctions. Introducing TMDs into magnetic tunnel junction can bring the advantage of adjustable electrical resistance of magnetic tunnel junction which is technically important from the viewpoint of application. Plenty of TMDs based junctions including MoS2 were studied both experimentally and theoretically and found MR values are in the wide range of 10^0–10^5 %.
Besides a proper choice of 2D spacers, a search of ideal spin-polarized electrons source is of high importance as well. For that purpose, half-metallic materials have been under consideration for decades including Heusler alloys such as Co2FeGe1/2Ga1/2, Co2MnSi, CoFeMnSi, Co2FeAl1/2Si1/2 and others.
In this work, novel magnetic tunnel junction based on Co2FeGe1/2Ga1/2 Heusler alloy electrodes and MoS2 spacer is proposed and theoretically studied as a promising element for spintronics devices. By DFT method electronic and magnetic properties of the MoS2/CFGG interface are explored both for the case of the FeGeGa‑ and Co‑termination of the CFGG surface. Robust ferromagnetism is demonstrated through the whole thickness of the CFGG film. Spin polarization is shown to be suppressed at the outermost few atomic layers of CFGG caused by interfacial interactions together with its quick recovery within four atomic layers (upward of 5 Å). Next, spin-dependent ballistic transport of CFGG/MoS2/CFGG MTJ is studied within the non-equilibrium green function formalism for MoS2 spacers varying from monolayer to four-layer films. In the zero-bias case, the MR values are found to be in the range of 10^4‑10^5 %. The I-V curves are derived as well demonstrating preservation of the large MR values under bias voltage. Together with recent advances in the graphene/CFGG heterostructure synthesis the current work supports further experimental and theoretical studies of half-metallic Heusler alloy based magnetic junctions possessing high effectiveness in spintronics applications.
Transport properties of CFGG/MoS2/CFGG MTJ with FeGeGa-termination. (a) Atomic structure of studied MTJ. (b) Zero-bias spin-resolved conductance for mono-, bi- and three-layer MoS2 spacer. Both parallel (left column) and antiparallel (right column) conductance is presented. (c) Г-centered k||-resolved zero-bias conductance at the Fermi level for parallel scheme with MoS2 monolayer. Majority- and minority-spin conductance are indicated as G↑↑ and G↓↓, respectively
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