Control of Interfacial Ferromagnetism via Metal-Insulator Transition in In Situ Grown LaNiO₃/CaMnO₃ Superlattices

In the design and synthesis of spintronic devices on the nanoscale, emergent magnetic interfacial phenomena in oxide heterostructures are of great interest. Employing in situ pulsed laser deposition (PLD) in conjunction with polarization-dependent angle-resolved photoelectron spectroscopy (ARPES) and X-ray magnetic circular dichroism (XMCD), we investigate LaNiO₃/CaMnO₃ superlattices with systematically varying thicknesses of LaNiO₃. Of particular interest is the thickness-dependent metal-insulator transition found in LaNiO₃, which could be used to control the emergent interfacial ferromagnetic state in CaMnO₃ through the modulation of charge transfer across the interface. At a critical thickness of four unit cells, we observe the onset of the metal-insulator transition and the opening of a bandgap in LaNiO₃. At a thickness of two unit cells, we observe a complete destruction of the Fermi surface, accompanied by a dimensional crossover, where the orbital polarization of the near-Fermi-level Ni 3d states switches to primarily in-plane. The results are supported by first-principles dynamical mean-field theory calculations. A concomitant suppression of the interfacial ferromagnetic state is observed below the critical thickness.