Significant effect of ordered micro‐domain on cell boundary phase distribution and demagnetization curve squareness of Sm ₂ Co ₁₇ ‐type magnet

Abstract

Abstract Cu‐rich cell boundary phase is difficult to precipitate evenly, resulting in a generally poor demagnetization curve squareness for Fe‐rich Sm 2 Co 17 ‐type magnet, which is a key factor limiting the further improvement of magnetic energy product. In this study, we report that nanoscale strip‐like ordered micro‐domains distributed in 1:7H disordered matrix phase of the solid solution precursor is a new factor significantly affecting the precipitation and distribution of the cell boundary phase. Long strip‐like and continuous micro‐twin structure with twin boundaries neatly perpendicular to the C ‐axis is observed after sintering treatment. After solution treatment, sequential and long strip‐like micro‐twins gradually transform into disordered state along the basal plane, forming narrow disordered 1:7H (TbCu 7 ‐type structure) phase between the separated strip‐like ordered micro‐domains. This disordering transformation takes place via broken down of the long strip‐like ordered micro‐domains, which is accomplished by narrowing along the width direction followed by reduction of the length. Furthermore, a new model revealing the effect of the ordered micro‐domains on the formation of the cell boundary phase is proposed. Antiphase boundaries enriched in Cu have already existed in the precursor with long strip‐like ordered micro‐domains. Therefore, the Cu‐rich cell boundary phase acting as strong pinning centers cannot be precipitated homogeneously and distributed continuously after aging, resulting in a poor demagnetization curve squareness of Sm 2 Co 17 ‐type magnet. Our results indicate that significant broken down of the nanoscale ordered micro‐domains in solution precursor is the key factor improving the distribution of cell boundary phase in Sm 2 Co 17 ‐type magnets.

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