Spintronics holds profound significance for the development of future electronic devices, among which magnetic tunnel junctions (MTJs) represent a crucial spintronic device. Intending to achieve excellent performance, e.g., higher tunnel magnetoresistance (TMR) and spin filtering effects, researchers have focused on molecular MTJs (MMTJs). Here, we adopt 6,6,12-graphyne (6,6,12-GY) nanodots as the barrier material in the central scattering region, while zigzag-edged graphene nanoribbons (ZGNRs) are chosen as electrode materials. Two kinds of devices labeled as M1n and M2n are constructed, which differ in the termination of the nanodots in the central scattering region. Since the magnetization directions of the two ZGNRs electrodes can be arranged either parallel (P) or antiparallel (AP), both M1n and M2n devices exhibit two distinct magnetic configurations. In this paper, the structures were optimized using first-principles calculations based on density functional theory (DFT), as implemented in the Vienna Ab-initio Simulation Package (VASP). By combining DFT with the nonequilibrium Green’s function (NEGF) method, we studied the spin transport properties of MMTJs.
The calculated results show that high TMR effects are obtained in both kinds of devices, with the values reaching up to 10⁸% in M1n and 10⁹% in M2n. The total current calculations indicate that a distinct difference emerges between the P and AP configurations after applying a bias voltage, which leads to the superior TMR. These findings provide valuable insights for the development of highly sensitive spintronic devices in the future. From the perspective of spin current, it can be observed that for both M1n and M2n devices with AP configuration, opposite-direction spin currents can be obtained by applying positive or negative bias voltage. Namely, in the AP configuration, both devices achieve the ±100% spin polarization (SP), indicating a dual spin filtering effect. In the P configuration, the spin-up and spin-down currents in M1n exhibit similar trends with the increasing bias, while M2n can produce a pure spindown current as the number of nanodots increases. The 100% spin filtering efficiency achieved in these carbon-based devices holds significant implications for increasing the storage density and operation speed of future spintronic devices. Notably, apart from the bias voltage, the spin current of M2n could also be controlled by switching the magnetization direction of the electrodes. In addition, the current in M2n is much smaller than that in M1n, which implies low consumption in device applications. Our investigation on the spin-dependent transport properties of 6,6,12-GY-based MMTJs paves the way for the promising spintronic applications of carbon-based materials.