Nanostructured graphene for spintronics

Abstract

Zigzag edges of the honeycomb structure of graphene exhibit magnetic polarization, making them attractive as building blocks for spintronic devices. Here, we show that devices with zigzag-edged triangular antidots perform essential spintronic functionalities, such as spatial spin splitting or spin filtering of unpolarized incoming currents. Near-perfect performance can be obtained with optimized structures. The device performance is robust against substantial disorder. The gate-voltage dependence of transverse resistance is qualitatively different for spin-polarized and spin-unpolarized devices, and can be used as a diagnostic tool. Importantly, the suggested devices are feasible within current technologies. DOI: 10.1103/PhysRevB.95.121406 Introduction. The weak intrinsic spin-orbit coupling and long spin diffusion lengths suggest graphene as an ideal spintronic material [1][2][3][4][5][6][7][8][9][10]. Spin splitting or filtering in graphene is predicted for half-metallic nanoribbons [2,[11][12][13] [24][25][26], and, in particular, nanostructured zigzag (zz)-edged devices [11][12][13]15,16,[27][28][29][30][31][32][33] are among the proposed graphene-based half metals. Spin filters have been proposed using triangular dots [15,31] or perforations [29] with many similarities, e.g., low-energy localized magnetic states and a net sublattice imbalance. However, perforations, or antidots [34][35][36], have the advantage over dots of being embedded in the graphene sheet which allows a wide range of spin-dependent transport properties. Although signatures of localized magnetic states have been detected [37][38][39], spin manipulation in graphene-based half metals has yet to be realized in experiments.In this Rapid Communication, we investigate the transport properties of graphene devices with embedded zz-edged triangular antidots. Such devices are within the reach of stateof-the-art lithographic methods: Triangular holes in graphene have recently been fabricated [40], and experiments suggest the possibility of zz-etched nanostructures [41,42]. Another possibility is to employ a lithographic mask of patterned hexagonal boron nitride, which naturally etches into zz-edged triangular holes [43,44]. The zz-edged structures support local ferromagnetic moments [3], however, global ferromagnetism is induced when the overall sublattice symmetry of the edges is broken [11][12][13]16,27,28,45]. This occurs for zzedged triangles [15,[29][30][31][32][33]. We have recently discussed the electronic structure of triangular graphene antidot lattices (GALs) [33]-here, we focus on transport through devices

Charge and spin transport anisotropy in nanopatterned graphene

“…Furthermore, we note that, for zz-TGAs, the iSHE-type behaviour emerges in the absence of a corresponding SHE-type behaviour for the charge current and zero bulk transverse resistivities. Therefore zz-TGA devices offer the possibility not just to filter different spin channels into different leads, as discussed in [9], but of generating a transverse resistance whose sign depends on the spin-polarisation of the input current.…”

“…This etch is performed four times. Previous studies [9] indicate that side-length variation has only a minor impact on the qualitative transport-scattering mechanisms of small-scale zz-TGAs. On the other hand, edge disorder has a more dramatic effect, reducing the corresponding magnetic moment distributions and affecting the spin-polarization properties.…”

“…However, this discrepancy requires asymmetric couplings between sets of probes which we would generally expect to be symmetric (e.g. T T T T T T T T T T T T T T T T T T T 10 42 34 13 21 24 43 and quickly find R xy =0 from equation (9).…”

“…Such a behavior can be used to engineer electronic circuits and waveguides [1], optical circuits [2], and communications devices [3]. It is particularly promising in two-dimensional materials, where the reduced dimensionality allows significant tuning of their electronic properties with only minor structural modifications [4][5][6][7][8][9][10]. Indeed, much of the recent excitement surrounding monolayer black phosphorus, or phosphorene, relates to its intrinsic electronic anisotropy arising from a buckled geometry [11,12].…”

“…However, the three edges of a zz-edged triangular graphene antidot (zz-TGA) are all associated with a single sublattice, which dictates large ferromagnetic moments [8, 33-37] (see figure 1). Recent works have demonstrated that lattices of approximately 1 nm side length zz-TGAs provide an excellent platform for electronic and spintronic applications due to robust band gaps, half-metallicity, and spinsplitting properties [8,9]. In the case of spin-splitting, incoming currents can be directed into output leads according to their spin orientation.…”