摘要
We investigated the interfacial magnetic exchange interaction between the organic semiconductor, tri(8-hydroxuquinoline)iron(III) (Feq3) on nickel film which displays perpendicular magnetization near the critical thickness of spin reorientation transition. By varying the adlayer thickness, we observed a redox process at interface that induced the formation of an interfacial hybrid state which involves the change of valence state and local crystal geometry in central iron of Feq3. The redox process indicates the electron transfer from Ni surface to adsorbed Feq3, resulting in trivalent Fe(III) to divalent Fe(II) and octahedral to tetrahedral coordination. Besides, our results demonstrate a strong ferromagnetic coupling at the interface between adsorbed Feq3 and Ni surface. Hysteresis loops exhibit a second hysteretic transition in 1.75 Å-thick Feq3 on Ni when subjected to vary magnetic fields, indicating the presence of pinning spins within the interface of Feq3/Ni magnetic moment. These pinning spins also enhanced the coercivity field. The mechanistic study via DFT calculations further illustrate the strong adsorption energy of divalent Fe(II)q3 with tetrahedral coordinate and imbalanced spin polarized electrons transfer from Ni surface to adsorbed Feq3 via N and O ligands that plays the key roles for the strong exchange coupling and significant magnetic hardening in Ni/Feq3 heterojunctions. © 2025 Elsevier B.V.