Directional Spin Transport in Zigzag GeC Nanoribbons via Edge Engineering: A DFT-NEGF Perspective

Density functional theory (DFT) and non-equilibrium Green's function (NEGF) formalism have been employed to investigate the prospects of zigzag germanium carbide nanoribbons (ZGeCNR) for spin filtering applications. We have considered total four possible configurations; firstly, symmetric edge-terminated configurations (H-ZGeCNR-H, 2H-ZGeCNR-2H) and secondly, asymmetric edge-terminated configurations (2H-ZGeCNR-H, H-ZGeCNR-2H). Based on energy calculation, we have predicted that 2H-GeCNR-H exhibits magnetic ground state with preferred ferromagnetic (FM) coupling $\Delta$E = 0.137 meV. Calculated spin-polarized $E-k$ diagram and DOS profile calculation for 2H-GeCNR-H configuration implies a unique semi-metallic character for spin-down, whereas spin-up posses a wide bandgap of 2.33eV. This interesting half-metallic (HM) behaviour of compounded group-4 nanomaterials (such as SiC, GeC) are different from group-4 elemental counterparts such as (silicene, germanene), which exhibit bipolar magnetic semiconducting behaviour upon asymmetric termination. To demonstrate the behaviour of 2H-GeCNR-H as a spin-filter, $I-V$ calculations using two probe device model was performed with both parallel (P-case) and antiparallel (AP-case) spin orientation of the electrodes. The recorded values of $I-V$, transmission spectra clearly highlight the presence of only spin-down current in the channel for both P and AP cases, indicating almost 100% spin filtering efficiency. These results warrant 2H-ZGeCNR-H applicability for high-efficiency spin filters.