Structural, electronic, and magnetic properties of tris(8-hydroxyquinoline)iron(III) molecules and their magnetic coupling with ferromagnetic surface: First-principles study

Using first-principles calculations, we have systematically investigated the structural, electronic, and magnetic properties of facial (fac-) and meridional (mer-) tris(8-hydroxyquinoline)iron(III) (Feq₃) molecules and their interaction with ferromagnetic substrate. Our calculation results show that for the isolated Feq₃, mer-Feq₃ is more stable than the fac-Feq₃; both Feq₃ isomers have a high spin-state of 5 μ _B as the ground state when an on-site Hubbard-U term is included to treat the highly localized Fe 3d electrons; while the standard DFT calculations produce a low spin-state of 1 μ _B for mer-Feq₃. These magnetic behaviors can be understood by the octahedral ligand field splitting theory. Furthermore, we found that fac-Feq₃ has a stronger bonding to the Co surface than mer-Feq₃ and an anti-ferromagnetic coupling was discovered between Fe and Co substrate, originating from the superexchange coupling between Fe and Co mediated by the interface oxygen and nitrogen atoms. These findings suggest that Feq₃ molecular films may serve as a promising spin-filter material in spintronic devices.