Spin Filters, Spin Valves, and Reconfigurable Logic Gates Realized in a Dual-Gate-Controlled Bipolar-Magnetic-Molecule Junction

The continuous miniaturization of electronic components drives the exploration of molecular-scale devices capable of performing complex computational functions. Harnessing the spin degree of freedom in single molecules offers a promising path toward multifunctional spintronics. Here, we theoretically design a single-molecule device with dual-gate-controlled multiple functionalities based on a bipolar magnetic molecule (BMM), in which two nickelocene (NiCp2) groups are serially connected with alkyl chains. Using density functional theory (DFT) combined with the nonequilibrium Green's function (NEGF) method, we show that independent gate voltages applied to each NiCp2 group enable precise control over the alignment of their spin-polarized frontier orbitals with respect to the Fermi level. Under symmetric gate voltages (-4, -4 V) or (6, 6 V), the device delivers nearly 100% spin-up or spin-down polarized current, functioning as a polarization reversible spin filter. Under asymmetric gate voltages (-4, 6 V) or (6, -4 V), opposite spin polarizations on the two NiCp2 groups induce spin blockade, resulting in a spin valve with an ON/OFF ratio reaching as high as 7.4 × 103. Furthermore, by redefining the two gate voltages as binary inputs, the device performs XNOR logic when using the total current at 0.1 V as output, and AND logic when using the spin-up current as output. Additionally, pronounced negative differential resistance (NDR) is observed under symmetric gate voltages, with peak-to-valley ratios exceeding 40. This work establishes NiCp2-based junctions as versatile platforms integrating spin filtering, spin valve, NDR, and reconfigurable logic, offering a pathway toward adaptive molecular spintronic circuits.