Hydrothermal synthesis of hexagonal CeO₂ nanosheets and their room temperature ferromagnetism

Hexagonal CeO₂ nanosheets of 40–50 nm in thickness and 300–400 nm in side-length have been successfully synthesized via controlling the morphology of CeCO₃OH precursors by a facile hydrothermal technique using CeCl₃·7H₂O as cerium source, ammonium hydrogen carbonate as precipitants, and ethylenediamine as complexant. The reaction time and the amount of CeCl₃·7H₂O and ethylenediamine were systematically investigated. The as-synthesized hexagonal CeO₂ nanosheets were examined by XRD, SEM, TEM, XPS, Raman scattering and magnetization measurements. It is found that the amount of CeCl₃·7H₂O and ethylenediamine are key parameters for controlling the final morphology. The hexagonal CeO₂ nanosheets have a fluorite cubic structure and there are Ce³⁺ ions and oxygen vacancies in surface of samples. The synthesized CeO₂ shows excellent room temperature optical properties. M–H curve exhibits excellent room-temperature ferromagnetism (RTFM) with saturation magnetization (M_s) of 3.02 × 10⁻² emu/g, residual magnetization (M_r) of 0.68 × 10⁻² emu/g and coercivity (H_c) of 210 Oe, which is likely attributed to the effects of the Ce³⁺ ions and oxygen vacancies. - Highlights: • Hexagonal CeO₂ nanosheets with superexerllent RTFM are synthesized by a facile hydrothermal method. • RTFM mechanism of CeO₂ nanosheets can be attributed to the influences of oxygen vacancies and Ce³⁺ ions. • A defect driven dissolution–recrystallization mechanism is suggested to explain the transformation from nanowires to nanosheets