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最近, 二维铁磁材料的发现加速了自旋电子学在超低功耗电子器件方面的应用. 其中, Fe3GeTe2通过实验调控, 比如界面层间耦合和离子液体调控, 可以使其居里温度达到室温, 具有广泛的应用前景. 本文基于密度泛函理论与非平衡格林函数方法, 研究了Fe3GeTe2/石墨烯二维异质结在有无氮化硼作隧穿层情况下的输运性质. 结果表明: 当Fe3GeTe2/石墨烯之间为透明接触时, 由于电子轨道杂化, 在 ± 0.1 V偏压下可以实现有效的自旋注入. 通过加入氮化硼作为隧穿层, 则可以在更宽偏压范围[–0.3 V, 0.3 V]内实现高效自旋隧穿注入; 并且, 由于Fe3GeTe2与石墨烯电子态在布里渊区的空间匹配程度取决于电子自旋方向, 相应出现的自旋过滤效应导致了接近100%的自旋极化率. 这些研究结果有望推动二维全自旋逻辑以及相关超低功耗自旋电子器件的发展.Recently, the discovery of intrinsic two-dimensional (2D) ferromagnetism has accelerated the application of spintronics in ultra-low power electronic device. Particularly, the Curie temperature of Fe3GeTe2 can be improved to room-temperature in several ways, such as interfacial exchange coupling and ionic liquid gating, which makes Fe3GeTe2 desirable for the practical application. In this work, we investigate the transport properties of Fe3GeTe2/graphene heterostructures with or without h-BN layers by utilizing the density functional theory combined with nonequilibrium Green’s function method. The results show that due to electronic orbital hybridization, the spin can be effectively injected into graphene with ± 0.1 V bias at the transparent contact interface of Fe3GeTe2/graphene. What is more, the efficient spin tunneling injection can be achieved in a wider bias range [–0.3 V, 0.3 V] by adding h-BN as a tunneling layer, where the spin filter effect that is induced by mismatched distribution of spin-dependent electronic states in the Brillouin zone, leads a spin polarizability to approach 100%. These results are helpful in the applications of 2D all-spin logic and the development of ultra-low power spintronic devices.
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Keywords:
- two-dimensional magnet /
- spin injection /
- spin filter effect /
- first principles calculation
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图 1 Fe3GeTe2/氮化硼(3)/石墨烯器件的(a)侧视图和(b)俯视图, 其中器件的电极区域由虚线框标出; 在器件的中心透射区Fe3GeTe2和石墨烯之间有0层或者3层氮化硼, 这里所示的模型是具有3层氮化硼的器件结构
Fig. 1. (a) The side view and (b) top view of Fe3GeTe2/h-BN(3)/graphene devices. The electrode regions of the device are indicated by a dashed frame. The number of h-BN layers between graphene and Fe3GeTe2 in the center region is 0 or 3. The model shown here is the device structure with 3 layers h-BN.
图 2 (a) 透明接触器件的I-V曲线; (b) 透明接触器件石墨烯沟道中的自旋极化率; (c) 隧穿接触器件的I-V曲线; (d) 隧穿接触器件石墨烯沟道中的自旋极化率
Fig. 2. (a) I-V curves of the transparent contact device; (b) spin polarization in graphene channel of the transparent contact device; (c) I-V curves of the tunneling contact device; (d) spin polarization in graphene channel of the tunneling contact device.
图 3 (a)透明接触器件和(b)隧穿接触器件的透射谱, 其中左边一列是自旋向上通道的透射谱, 右边一列是自旋向下通道的透射谱
Fig. 3. Transmission spectra of (a) the transparent contact devices and (b) the tunneling contact devices. The left column is the transmission spectra of the spin up channel and the right column is the transmission spectra of the spin down channel.
图 4 (a) Fe3GeTe2/石墨烯异质结能带; (b) Fe3GeTe2/氮化硼/石墨烯异质结能带; (c) Fe3GeTe2/石墨烯异质结差分电荷密度, 其中绿色代表电子损耗, 黄色代表电子积聚; (d) 费米能级上k点依赖的Fe3GeTe2态密度分布; 图4(a) 和图4 (b) 中左边一列为自旋向上能带, 右边一列为自旋向下能带
Fig. 4. (a) Band structure of Fe3GeTe2/graphene heterojunction; (b) band structure of Fe3GeTe2/boron nitride/graphene heterojunction; (c) the differential charge density of Fe3GeTe2/graphene heterojunction, where the green and yellow represent electron depletion and accumulation respectively; (d) the k dependent density of states distribution at the Fermi level in Fe3GeTe2. In Fig. 4(a) and Fig. 4(b), the left column represents the spin up bands, and the right column represents the spin down bands.
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[1] Novoselov K S, Geim A K, Morozov S V, Jiang D, Zhang Y, Dubonos S V, Grigorieva I V, Firsov A A 2004 Science 306 666
Google Scholar
[2] Li M, Su S, Wong H, Li L J 2019 Nature 567 169
Google Scholar
[3] Geim A K, Grigorieva I V 2013 Nature 499 419
Google Scholar
[4] Žutić I, Matos-Abiague A, Scharf B, Dery H, Belashchenko K 2019 Mater. Today 22 85
Google Scholar
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[20] Dlubak B, Martin M, Deranlot C, Servet B, Xavier S, Mattana R, Sprinkle M, Berger C, De Heer W A, Petroff F, Anane A, Seneor P, Fert A 2012 Nat. Phys. 8 557
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