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      Electrically induced 2D half-metallic antiferromagnets and spin field effect transistors


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          When conduction electrons in a solid are completely spin polarized, the single-spin transport results in great promise in spintronic (i.e., spin electronic) applications. Realizing high-efficiency spintronic devices based on 2D van der Waals (vdW) materials would tremendously impact nanoscale spintronics and the current information technologies. However, a minority of vdW materials are magnetic, among which antiferromagnets do not have net spin polarization whereas ferromagnets usually have limited imbalance between oppositely polarized electrons. Here, we show that antiferromagnetic vdW bilayers can be made half metallic, in which electrons of singular spin are metallic but those of the opposite spin are insulating, leading to 100% spin-polarized conduction electrons. Based on this finding, an interesting type of spin field effect transistor is proposed.


          Engineering the electronic band structure of material systems enables the unprecedented exploration of new physical properties that are absent in natural or as-synthetic materials. Half metallicity, an intriguing physical property arising from the metallic nature of electrons with singular spin polarization and insulating for oppositely polarized electrons, holds a great potential for a 100% spin-polarized current for high-efficiency spintronics. Conventionally synthesized thin films hardly sustain half metallicity inherited from their 3D counterparts. A fundamental challenge, in systems of reduced dimensions, is the almost inevitable spin-mixed edge or surface states in proximity to the Fermi level. Here, we predict electric field-induced half metallicity in bilayer A-type antiferromagnetic van der Waals crystals (i.e., intralayer ferromagnetism and interlayer antiferromagnetism), by employing density functional theory calculations on vanadium diselenide. Electric fields lift energy levels of the constituent layers in opposite directions, leading to the gradual closure of the gap of singular spin-polarized states and the opening of the gap of the others. We show that a vertical electrical field is a generic and effective way to achieve half metallicity in A-type antiferromagnetic bilayers and realize the spin field effect transistor. The electric field-induced half metallicity represents an appealing route to realize 2D half metals and opens opportunities for nanoscale highly efficient antiferromagnetic spintronics for information processing and storage.

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            Electronic analog of the electro-optic modulator

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              Is Open Access

              Half-Metallic Graphene Nanoribbons

              Electrical current can be completely spin polarized in a class of materials known as half-metals, as a result of the coexistence of metallic nature for electrons with one spin orientation and insulating for electrons with the other. Such asymmetric electronic states for the different spins have been predicted for some ferromagnetic metals - for example, the Heusler compounds- and were first observed in a manganese perovskite. In view of the potential for use of this property in realizing spin-based electronics, substantial efforts have been made to search for half-metallic materials. However, organic materials have hardly been investigated in this context even though carbon-based nanostructures hold significant promise for future electronic device. Here we predict half-metallicity in nanometre-scale graphene ribbons by using first-principles calculations. We show that this phenomenon is realizable if in-plane homogeneous electric fields are applied across the zigzag-shaped edges of the graphene nanoribbons, and that their magnetic property can be controlled by the external electric fields. The results are not only of scientific interests in the interplay between electric fields and electronic spin degree of freedom in solids but may also open a new path to explore spintronics at nanometre scale, based on graphene.

                Author and article information

                Proc Natl Acad Sci U S A
                Proc. Natl. Acad. Sci. U.S.A
                Proceedings of the National Academy of Sciences of the United States of America
                National Academy of Sciences
                21 August 2018
                3 August 2018
                : 115
                : 34
                : 8511-8516
                [1] aKey Laboratory of Polar Materials and Devices, Ministry of Education, Department of Electronic Engineering, East China Normal University , Shanghai 200062, China;
                [2] bCollaborative Innovation Center of Extreme Optics, Shanxi University , Taiyuan, Shanxi 030006, China;
                [3] cNanoscale Science and Engineering Center, University of California, Berkeley , CA 94720;
                [4] dMaterials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, CA 94720
                Author notes
                2To whom correspondence may be addressed. Email: sjgong@ 123456ee.ecnu.edu.cn , cgong@ 123456berkeley.edu , or xiang@ 123456berkeley.edu .

                Edited by Jim Eckstein, University of Illinois Urbana–Champaign, Urbana, IL, and accepted by Editorial Board Member Zachary Fisk June 19, 2018 (received for review September 7, 2017)

                Author contributions: S.-J.G., C.G., and X.Z. designed research; S.-J.G., C.G., and Y.-Y.S. performed research; S.-J.G., C.G., W.-Y.T., C.-G.D., J.-H.C., and X.Z. analyzed data; and S.-J.G., C.G., and X.Z. wrote the paper.

                1S.-J.G. and C.G. contributed equally to this work.

                Author information
                PMC6112705 PMC6112705 6112705 201715465

                Published under the PNAS license.

                Page count
                Pages: 6
                Physical Sciences
                Applied Physical Sciences

                antiferromagnetic spintronics,spin field effect transistor,half metallicity,2D magnetism,2D materials


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