Electrical sensitization of magnetic nanoplatelets with surface-selective hybridization for magneto- and electro-optic sensing

We report a new strategy for coupling magnetic and electric dipoles within a single nanoparticle by exploiting structural and chemical anisotropy. The approach is based on ferrimagnetic barium hexaferrite nanoplatelets (NPLs) selectively hybridized on only one basal plane with organic polar ligands bearing a large electric dipole and a phosphonic anchoring group. The resulting Janus magneto-electric hybrids exhibit magnetic and electric dipoles normal to the basal plane of the NPLs. To experimentally realize these hybrids, we developed a surface-selective hybridization protocol at the solid–liquid interface. Each processing step—including substrate surface optimization, magnetically-directed monolayer assembly of NPLs, surface-selective hybridization, and particle harvesting—was systematically investigated. In parallel, we established an optical method to probe and verify the simultaneous response of the hybrid NPL dispersions to external electric and magnetic fields employing a unique transport mechanism, a multidipole electrophoresis in a magnetic field (MEMF). Field-induced birefringence changes were also measured, demonstrating coupled magneto-electric and optical responses. These findings identify Janus magneto-electric NPLs as a versatile materials platform for contactless optical sensing, including external-field sensors, as well as for photonic devices enabling advanced light manipulation.