Key Laboratory of Magnetism and Magnetic Materials of the Ministry of Education, School of Physical Science and Technology and Electron Microscopy Centre of Lanzhou University, Lanzhou University, Lanzhou 730000, P. R. China.
Nanoscale. 2019 Mar 7;11(10):4385-4393. doi: 10.1039/c8nr09922g.
Identifying the dopants and their occupation sites in rare-earth-doped permanent magnets is critical not only to understand the mechanism of tuning their magnetic properties, but also to develop guiding principles to further improve their performance. In this study, we present a direct observation of the preferred atomic sites of La atoms in La-doped M-type SrFe12O19 hexaferrite. Our data solidly clarified that only the Sr2+ cations were replaced by La3+ cations, and the La-doping caused the changes in the valence states of iron cations located at the 4f1 and 2a crystallographic sites. First principles calculations further revealed that after La-doping, the changes in the spin states of the Fe3+ cations located at the 4f1 tetrahedral sites resulted in magnetization enhancement and those of the 2a octahedral sites contributed to electrical neutrality, well matching the experimental atomic-column resolution EELS and magnetic measurement results.
确定掺杂元素及其在稀土掺杂永磁体中的占据位置，不仅对于理解其磁性调节机制至关重要，而且对于开发进一步提高其性能的指导原则也具有重要意义。在本研究中，我们直接观察到镧掺杂 M 型锶铁氧体 SrFe12O19 中镧原子的优先原子位置。我们的数据明确表明，只有 Sr2+ 阳离子被 La3+ 阳离子取代，而镧掺杂导致位于 4f1 和 2a 晶位的铁阳离子的价态发生变化。第一性原理计算进一步表明，镧掺杂后，位于 4f1 四面体位置的 Fe3+ 阳离子的自旋态变化导致磁化强度增强，而位于 2a 八面体位置的 Fe3+ 阳离子的自旋态变化有助于电中性，这与实验原子柱分辨率 EELS 和磁性测量结果非常吻合。
