Cell-boundary-structure controlled magnetic-domain-wall-pinning in 2:17-type Sm-Co-Fe-Cu-Zr permanent magnets

• Published in: Materials characterization 2020-11, Vol.169, p.110575, Article 110575
• Main Authors: Song, Xin, Liu, Yao, Xiao, Andong, Yuan, Tao, Ma, Tianyu
• Format: Article
• Language: English
• Subjects: Magnetic domain; Magnetic properties; Microstructure; Permanent magnets; Rare earth; Sm-Co alloys
• ISSN: 1044-5803; 1873-4189
• DOI: 10.1016/j.matchar.2020.110575

Raising Fe content is essential to achieve large magnetization and high energy product in the nanocell structured 2:17-type Sm-Co-Fe-Cu-Zr alloys — the most prominent permanent magnets for advanced high temperature applications. However, it remains a mystery why the Fe-rich magnets with complete nanocell structure still have a maximum energy product much lower than the ideal value. Here we performed a comparative investigation between two Sm-Co-Fe-Cu-Zr magnets with Fe contents of 16.2 wt% and 19.5 wt%, having similar diamond-shaped cell boundaries but distinct magnetic properties. Unlike the Fe-16.2 wt% magnet that most cells are separated by 1:5H cell boundaries, some cells in the Fe-19.5 wt% magnet are separated by the 2:17R’-type (disordered rhombohedral phase) cell boundaries. Unlike the 1:5H cell boundaries that show strong attractive domain-wall-pining, the 2:17R’ cell boundaries yield repulsive pinning, leading to poor squareness as well as the lower-than-ideal maximum energy product. With further development, the knowledge that Fe content controls the cell boundary structure and pinning type may help to improve the magnetic performance of Fe-rich Sm-Co-Fe-Cu-Zr permanent magnets. The inferior squareness factor (SF) and maximum energy product of the Fe-19.5 wt% magnet to those of the Fe-16.2 wt% magnet (a) is due to the local cell boundary structure change from 1:5H to 2:17R’, which alters the favorable attractive domain wall pinning (b) into unfavorable repulsive type accordingly (c). [Display omitted] •Fe content controls the cell boundary structure of the 2:17-type Sm-Co-Fe-Cu-Zr magnets.•Some cell boundaries change from 1:5H to 2:17R’ when raising Fe content from Fe-16.2 wt% to Fe-19.5 wt%.•The domain-wall-pinning type changes from attractive for 1:5H cell boundary to repulsive for 2:17R’ cell boundary.•The attractive domain-wall-pinning results in better squareness than the repulsive domain-wall-pinning.