Firstprinciplestudyof effects of Ca-Co (Zn) co-doping on properties of M-type strontium ferrite
Authors: LI Xinyu , HOU Yuhua , CHEN Xuan , HUANG Youlin , LI Wei , TAO Xiaoma ,   School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063, China,   Department of Physics, Guangxi University, Nanning 530004, China
Published: January 2025

M-type strontium ferrite has attracted widespread attention in the field of permanent magnet materials due to its unique magnetic properties, dielectric performance, and thermal stability. However, compared with rare-earth permanent magnets such as Nd<sub>2</sub>Fe<sub>14</sub>B, strontium ferrite (SrFe<sub>12</sub>O<sub>19</sub>) permanent magnets possess relatively low comprehensive magnetic properties, which limits their application range. The effects of Ca-Co (Zn) doping on the electronic structure, mechanical properties, and magnetic properties of M-type strontium ferrite are systematically investigated by first-principles plane-wave pseudopotential method based on density functional theory (DFT), combined with the generalized gradient approximation (GGA + <i>U</i>) in thiswork. The calculation results indicate that the Ca-Co (Zn) co-doped M-type strontium ferrite systems exhibit good structural stability and mechanical properties. In the Ca-Zn co-doped structures, the conductivity of the system is enhanced because of the substitution of divalent Zn ionsfortrivalent Fe ions at the 4<i>f</i><sub>1</sub> site. The Ca-Co (Zn) co-doping increases the total magnetic moment of the system, while the magnetocrystalline anisotropy energy decreases. However, compared with the single Codoped systemand singleZn doped system, theCo-Znco-doped systemhas themagnetocrystalline anisotropy energy improved, indicating that Ca-Co (Zn) co-doping can effectively enhance the magnetic properties of strontium ferrite. In thiswork, the mechanisms of the effects of Ca-Co and Ca-Zn co-doping on the magnetocrystalline anisotropy energy of strontium ferriteare also analyzed. The results indicate that the decrease ofmagnetocrystalline anisotropy energy in the Ca-Co co-doped system is mainly due to the effects of d<sub><i>xy</i></sub> and <inline-formula><tex-math id="Z-20250221220227">\begin{document}${\mathrm{d}}_x^2 $\end{document}</tex-math></inline-formula>-<inline-formula><tex-math id="Z-20250221220131">\begin{document}${_y} ^2 $\end{document}</tex-math></inline-formula> orbital electrons of Co<sup>3+</sup> ion and d<sub><i>xy</i></sub> and <inline-formula><tex-math id="Z-20250221220220">\begin{document}${\mathrm{d}}_x^2 $\end{document}</tex-math></inline-formula>-<inline-formula><tex-math id="Z-20250221220145">\begin{document}${_y} ^2 $\end{document}</tex-math></inline-formula> orbital electrons of Fe ions at the 2<i>b</i> site. In the Ca-Zn co-doped system, the reduction is mainly influenced by Fe-3d orbitals at the 4<i>f</i><sub>1</sub> site, while the d<sub><i>xy</i></sub> and <inline-formula><tex-math id="Z-20250221220159">\begin{document}${\mathrm{d}}_x^2 $\end{document}</tex-math></inline-formula>-<inline-formula><tex-math id="Z-20250221220153">\begin{document}${_y} ^2 $\end{document}</tex-math></inline-formula> orbital electrons of the 2<i>b</i> site enhance the magnetocrystalline anisotropy energy of the system. These results provide theoretical guidance for modifyingM-type strontium ferritein future.