Redox regulation of 3d0 ferrimagnetism in pristine ZnO nanofibres and electrospinning route of ZnO porous nanotubules

Abstract

Enhanced room-temperature ferrimagnetism was observed in ammoniated electrospun ZnO nanofibres (NFs) with an effective magnetic moment as high as 0.0315 μ_B per O at 10 K. It was demonstrated that a deep donor level oxygen anion vacancy defect complex related to an electron-trapped state, i.e. [V_O]⁺ or F-center (F_c) with volume fraction ∼1.58%, could likely be the intrinsic origin of 3d⁰ ferrimagnetism in pristine ZnO NFs. Moreover, an F_c redox-regulating mechanism suggested that hydrogen-assisted F_c partial generation, [V_O]⁰⁺ + H⁺ → [V_O]⁺ = 〈F_c〉, and oxygen-assisted F_c partial annihilation, 〈F_c〉 + e⁻ → [V_O]⁰⁺ , explain the enhanced and reduced diluted ferrimagnetism, respectively. Compared to conventional chemical manipulation, the atmospheric redox anneal-regulating F_c defect strategy will advance our understanding and feasible modulation of 3d⁰ ferrimagnetism on demand. Additionally, the electrospun fabrication of ZnO porous nanotubules (NTs) was reported via two-step calcination in air. Hollow NTs form due to the Kirkendall effect, and simultaneously nanopores along the axial direction form due to the Ostwald ripening where highly itinerant point defects (e.g., [V_O]⁰⁺) were generated at elevated temperatures.