Tailoring magnetic anisotropy of ferromagnetic films is a critical issue in constructing energy-efficient and high-density magnetic memory devices. Presently, the effective tunability was focused on a single-ion-manipulated electronic structure evolution. Here, we reported a new strategy of dual-ion-tuned orbital structure and magnetic anisotropy of ferromagnetic films. N-doped Fe/MgO bilayer films were deposited on shape memory alloy substrates which can generate a significant lattice strain on the films. Before the N ions participate into the manipulation, the Fe/MgO film shows an in-plane magnetic anisotropy, which may be due to excessive Fe-O orbital hybridization. Interestingly, the N and O ions synergistically manipulate electronic coordination of the Fe layer, which can be further modified by the lattice strain through a charge transfer among N-Fe-O. Under such effect, the magnetic anisotropy of the film is switchable from in-plane to perpendicular magnetic anisotropy (PMA). The X-ray line dichroism (XLD) characterization reveals that the anisotropy regulation is related to Fe 3d orbital evolution: N-Fe orbital hybridization promotes the Fe dz2 orbital occupation effectively, which is beneficial in increasing PMA by strengthening Fe-O orbital hybridization along the out-of-plane direction. However, the compressive strain induces a N-Fe-O charge transfer and reduces the Fe dz2 electronic occupation, which weakens the PMA of films. These findings provide a new dimensionality for regulating orbital performance of ferromagnetic materials and developing strain-assisted memory devices.
Keywords: charge transfer; dual-ion manipulation; magnetic anisotropy; orbital hybridization; orbital occupancy.