Multimodal analysis of Zr substitution effects on magnetic and crystallographic properties in (Sm1−Zr )(Fe0.8Co0.2)12 compounds with ThMn12 structure

SmFe ₁₂ -based compounds containing Zr atoms have been recognized as candidates for novel high-performance permanent magnet materials with a high saturation magnetization. Partial substitution of Sm with Zr in (Sm _{1− x}Zr _x)(Fe _0.8Co _0.2) ₁₂ has been known to enhance the magnetization of the compound. This study focused on (Sm _{1− x}Zr _x)(Fe _0.8Co _0.2) ₁₂ single-crystalline films to evaluate the effects of Zr substitution for Sm on their structural and magnetic properties via systematic multimodal analysis. X-ray absorption fine structure (XAFS) and scanning transmission electron microscopy indicated a selective occupation of the Sm site by Zr atoms without disturbing the Fe sublattices. The chemical shift in the Zr- K edge XAFS spectra suggested electron transfer from Zr to the Fe band. Soft X-ray magnetic circular dichroism analysis proved that the magnetic moment of Sm was two orders of magnitude smaller than the magnetic moments of Fe and Co, and its contribution to the total magnetization was negligible. The partial substitution of Sm with Zr resulted in a volumetric expansion and c-axis length elongation despite Zr having a smaller atomic radius, which is unique to (Sm _{1− x}Zr _x)(Fe _0.8Co _0.2) ₁₂ without structure-stabilizing elements such as Ti, V, and Si. This anisotropic expansion is explained by an increase in the magnetic moment and magnetic interactions in the Fe8 f site, which is induced by the electron transfer from Zr to Fe8 f atoms. Thus, we conclude that the electron transfer from Zr to the Fe8 f atoms principally drives magnetization enhancement in (Sm _{1− x}Zr _x)(Fe _0.8Co _0.2) ₁₂ single-crystalline films.