Abstract The structural and magnetic properties of Fe/Fe3O4 nanocomposites, synthesized by combined high energy ball milling and controlled oxidation, have been studied. An X-ray diffraction analysis of the crystal structure of the nanocomposites confirmed the coexistence of Fe and Fe3O4 phases. An increase of the oxygen concentration during oxidation process led to the formation of a higher fraction of the Fe3O4 phase with good crystallinity and stoichiometry. The morphology of the nanocomposites revealed a lamella-like structure with a thickness of about 30 nm. The saturation magnetization decreased when the phase fraction of Fe3O4 increased. The coercivity was enhanced at low temperatures (≤100 K) but decreased at high temperatures, due to thermal fluctuation effects on the anisotropy in the Fe3O4 phase. Interestingly, the lamellae exhibited a sharp Verwey transition near 120 K, which is often suppressed or absent in nanostructured Fe3O4 due to the poorly crystalline, off-stoichiometric characteristic. The temperature dependence of high-field magnetization of the lamellae is analyzed by the modified Bloch law. Our study demonstrates the possibility of tuning the magnetism in iron/iron oxide nanosystems through controlled oxidation.

中文翻译：

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Fe/Fe3O4薄片中的氧化控制磁性和Verwey转变

摘要 研究了结合高能球磨和可控氧化合成的 Fe/Fe3O4 纳米复合材料的结构和磁性能。纳米复合材料晶体结构的 X 射线衍射分析证实了 Fe 和 Fe3O4 相的共存。氧化过程中氧浓度的增加导致形成更高比例的具有良好结晶度和化学计量的 Fe3O4 相。纳米复合材料的形态显示出厚度约为 30 nm 的层状结构。当 Fe3O4 的相分数增加时，饱和磁化强度降低。由于热波动对 Fe3O4 相各向异性的影响，矫顽力在低温 (≤100 K) 下增强，但在高温下降低。有趣的是，薄片在 120 K 附近表现出尖锐的 Verwey 转变，由于结晶差、非化学计量特性，在纳米结构的 Fe3O4 中通常被抑制或不存在。薄片的高场磁化强度的温度依赖性通过修正的布洛赫定律进行分析。我们的研究证明了通过受控氧化调节铁/氧化铁纳米系统磁性的可能性。