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.