Department of Environmental Science and Engineering, Fudan University, Shanghai, 200433, China.
Department of Chemical Engineering, Graduate School of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi, Hiroshima, 739-8527, Japan.
Sci Rep. 2017 Aug 30;7(1):9894. doi: 10.1038/s41598-017-09897-5.
Highly crystalline single-domain magnetite FeO nanoparticles (NPs) are important, not only for fundamental understanding of magnetic behaviour, but also for their considerable potential applications in biomedicine and industry. FeO NPs with sizes of 10-300 nm were systematically investigated to reveal the fundamental relationship between the crystal domain structure and the magnetic properties. The examined FeO NPs were prepared under well-controlled crystal growth conditions using a large-scale liquid precipitation method. The crystallite size of cube-like NPs estimated from X-ray diffraction pattern increased linearly as the particle size (estimated by transmission electron microscopy) increased from 10 to 64.7 nm, which indicates that the NPs have a single-domain structure. This was further confirmed by the uniform lattice fringes. The critical size of approximately 76 nm was obtained by correlating particle size with both crystallite size and magnetic coercivity; this was reported for the first time in this study. The coercivity of cube-like FeO NPs increased to a maximum of 190 Oe at the critical size, which suggests strong exchange interactions during spin alignment. Compared with cube-like NPs, sphere-like NPs have lower magnetic coercivity and remanence values, which is caused by the different orientations of their polycrystalline structure.
高结晶单相磁铁矿 FeO 纳米颗粒（NPs）不仅对于理解磁性行为具有重要意义，而且在生物医学和工业领域也具有相当大的应用潜力。本文系统研究了尺寸为 10-300nm 的 FeO NPs，以揭示晶体畴结构与磁性之间的基本关系。所研究的 FeO NPs 是在使用大规模液相沉淀法在受控的晶体生长条件下制备的。X 射线衍射图谱中估算出的立方状 NPs 的晶粒尺寸随粒径（通过透射电子显微镜估算）从 10nm 增加到 64.7nm 呈线性增加，这表明 NPs 具有单畴结构。这进一步通过均匀的晶格条纹得到证实。通过将粒径与晶粒尺寸和磁矫顽力相关联，得出了约 76nm 的临界尺寸；这是在本研究中首次报道。在临界尺寸处，立方状 FeO NPs 的矫顽力增加到 190Oe 的最大值，这表明在自旋排列过程中存在强烈的交换相互作用。与立方状 NPs 相比，球形 NPs 的磁矫顽力和剩余磁化强度值较低，这是由于其多晶结构的不同取向所致。
