Engineering Fe(II) spin-crossover/2D reduced graphene oxide heterostructures for tunable cooperativity, magnetic coupling, and conductance switching

Abstract Despite demonstrating bistability in spin-crossover (SCO) materials, the absence of long-range magnetic order and poor electrical conductivity limit their prospect in spintronic and nanoelectronic applications. Intending to create hybrid devices made of SCO-2D architecture, here, we report an easily processable Fe-based SCO nanostructures grown on 2D reduced graphene oxide (rGO). X-ray photoelectron spectra of the hybrid clearly reveal the formation of new bonding state with possible charge transfer between rGO and SCO nanoparticles. This interfacial charge transfer enhances intermolecular interactions, resulting in increased cooperativity within the heterostructure. The temperature dependent Mössbauer spectra analysis distinctly uncovers the proportion of Fe (II) spin states within the hybrid nanocomposite samples, highlighting how the formation of a 2D network of SCO clusters enhances the cooperativity. Notably, both the thermal hysteresis and the mean spin-transition temperature are tunable through the application of a magnetic field, underscoring significant magnetic interactions. The inherently low conductivity of pristine SCO nanostructures is addressed by embedding them within a conductive rGO matrix. This facilitates the electrical detection of magnetic bistability through high-spin/low-spin conductance switching, even in the absence of an external magnetic field. As a result, spin functionality is integrated into the conductance behavior, paving the way for hybrid 2D spintronic devices. Finally, ab-inito calculations, on the experimentally motivated model systems provide insights into the microscopic mechanism confirming the enhanced magnetic interaction in the hybrid architecture facilitated by interfacial charge transfer.