Acceptor–Donor Molecular Heterojunction Control of π‑Orbital-Induced Magnetic Properties of a 3d Ferromagnet

Metal-organic molecule interfaces have given rise to a wide range of magnetic phenomena. These effects arise due to spin-polarized charge transfer and enhanced exchange interaction at metallo-molecular hybridization sites, where tunability via electric fields beyond ferroelectric interfaces remains to be demonstrated. Here, we explore manipulating the magnetism of cobalt with the intrinsic electric field generated at C60/phthalocyanine heterojunctions, a combination commonly used in organic photovoltaics. The results give evidence for a C60 layer thickness-dependent control of hybridization effects on cobalt. We find that the heterojunctions may attenuate the hybridization effects, with changes in coercivity and magnetization due to the built-in electric field. An emergent exchange bias is attributed to an enhanced Rashba interaction for thicker C60 layers. Our study clarifies some of the questions in the field of molecular "spinterface" physics and demonstrates that internal electric field generation is a promising method for manipulation of metallo-molecular interfaces up to room temperature.