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

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.