Direct imaging of dopant sites in rare-earth element-doped permanent magnet and correlated magnetism origin

Abstract

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.