Robust spin-filtering and current-switching in a photochromic Fe( ii ) spin-crossover complex

Transition metal spin-crossover (SCO) complexes with magnetic bistability show great promise as spin-switches for molecule-based devices. Using first-principles calculations combined with the non-equilibrium Green's function technique, we explored the spin-resolved electronic and transport properties of photochromic Fe(II) SCO complexes in the high-spin state with the open-ring (HS-O) isomer and in the low-spin state with the closed-ring (LS-C) isomer, since the photocyclization and photocycloreversion between the HS-O and LS-C isomers can be reversibly realized under light radiation with different wavelengths at room temperature as in previous experiments. Our results clearly reveal that the examined Fe(II) SCO complexes with photochromic diarylethene-based ligands in the HS-O isomer have lower energy than the LS-C isomer of 0.59 eV. A nearly perfect spin-filtering effect is observed in the proposed molecular junction in the HS-O isomer, in which the Fe(II) SCO complexes are sandwiched between two Au(111) electrodes. The current is carried predominantly by the spin-down electrons within the considered bias voltages, while the spin-up electrons are largely inhibited due to localized molecular orbitals near the Fermi level. At the same time, we also observed an obvious current-switching effect between the HS-O and LS-C isomers, since the current through the molecular devices in the HS-O isomer (acting as the ON state) is significantly larger than that in the LS-C isomer (OFF state). These findings highlight the great potential of this kind of photo-driven SCO complex in future molecular spintronics.