NaBH₄ induces strong ferromagnetism of Bi₂Fe₄O₉ at room temperature

Bi₂Fe₄O₉ nanosheets were prepared using a hydrothermal method, followed by the introduction of NaBH₄ and high-temperature calcination, which successfully induced strong ferromagnetism in the material at room temperature (M_S = 10.22 emu/g and M_r = 2.93 emu/g). This work demonstrates for the first time that Bi₂Fe₄O₉ can exhibit such strong ferromagnetism at room temperature, with potential for further enhancements. Meanwhile, the ferroelectric properties of the samples were investigated. X-ray diffraction confirmed that the samples were single-phase with no detectable impurities. Based on a series of characterization analyses, it is inferred that Bi vacancies contribute to the observed strong magnetism.