Field-Tunable Interfacial Magnetism and Adsorption-Induced Polarization Switching at Molecular Heusler Spinterfaces

We present a first-principles investigation of electric-field-induced interfacial orbital reconfiguration at molecular-Heusler spinterfaces, formed by Co- and Fe-centered bipyridine pincer complexes adsorbed on Co2FeSi(001) surfaces. Eight energetically favorable configurations are identified across distinct surface terminations (Fe–Si and Co–Co), exhibiting diverse adsorption geometries and magnetic behaviors. Strong hybridization between the molecular pz orbitals and the surface Co/Fe dz2 states leads to substantial charge transfer, inducing spin polarization and localized magnetic moments in these complexes. The magnetic anisotropy energy (MAE) shows pronounced adsorption-site dependence with the easy axis switching from in-plane to out-of-plane. Notably, in the axially aligned Co/(Fe–Si) chemisorbed geometry, an applied electric field reverses the Co magnetic moment from 1.7 to −2.0 μB. This magnetic switching is driven by the field-induced redistribution of Co-d orbital populations and charge transfer modulated by the surface termination. Concurrently, the MAE shifts from 0.4 meV (out-of-plane) to 2.1 meV (in-plane), reflecting an electric-field-driven change in anisotropy that correlates with enhanced spin-β electron occupation in the d-orbitals. Spin-dependent electronic transport calculations demonstrate strongly spin-polarized conduction and a significant tunnel magnetoresistance response, underscoring the potential of molecular Heusler junctions as versatile platforms for tunable molecular spintronic devices. These results highlight the cooperative influence of molecule–substrate interactions and external electric fields in tuning interfacial magnetism and spin anisotropy, offering insights for the rational design of electrically reconfigurable molecular spintronic platforms.