Gate-Controlled Spin Channel Switching in Single-Molecule Magnets in Molecular Junction

In molecular spintronics, achieving precise control over the spin polarization direction of transported electrons at the single-molecule level remains a great challenge. This study addresses this challenge by leveraging the unique electronic structure of bipolar magnetic molecules (BMMs). By performing density functional theory (DFT) calculations, we designed and screened a series of transition metal complexes, identifying Cr(II)(BBM)₂ (where BBM is the 2,2'-bibenzoimidazole anion) as a promising BMM candidate. Combining DFT with the non-equilibrium Green's function (NEGF) formalism, spin-polarized quantum transport calculations were carried out on a molecular junction where Cr(II)(BBM)₂ was coupled to graphite electrodes. Our results demonstrate that the application of an external gate voltage enables reversible switching of the spin transport direction. A gate voltage of -5 V yields a 100% spin-polarized current in the spin-up channel. Conversely, a small positive gate voltage of +0.05 V results in a completely polarized spin-down current. This gate-controlled spin channel switching, achieved through rational molecular design, underscores the potential of BMMs as fundamental components for future ultra-dense, low-power spintronic devices.