Uncovering optical, magnetic, and electrical properties of epitaxial nitrogen-doped lithium ferrite films

The powerful means of nitrogen doping has been applied to perovskite, rocksalt, anatase, and fluorite oxides to tailor crystal structures, electronic/chemical states, and resultant physical/chemical properties for electronic/optical/magnetic device, catalysis, and energy conversion. However, it is rare for nitrogen-doped spinel oxides, especially for spinel ferrites. Here, we take spinel lithium ferrite (LiFe5O8) as an archetype to elucidate the nitrogen doping effect on the optical, magnetic, and electrical properties. The nitrogen dopants in lithium ferrite oxynitride (LiFe5O8-xNy) epitaxial films have been systematically manipulated by adjusting the deposition atmospheres during growth. Remarkably, nitrogen doping leads to a significant enhancement in both light absorption (approximately twice as enhanced at 2.1 eV) and electrical performance (up to 6 order enhancement) for lithium ferrites. The combined experimental and theoretical studies reveal that the nitrogen doping effect can effectively narrow the bandgap and create in-gap states that give rise to enhanced light absorption and electrical performance. Our study sheds light on a profound understanding of nitrogen doping-tailored crystals and electronic structures of spinel ferrites and provides a novel, easy, and effective route to magnetic semiconducting ferrite oxynitrides with boosted light absorption and electrical performance, which can be beneficial to spintronic and photochemistry applications.