Enhancement of Magnetic Properties in (Sm, Dy, Gd, Er)(Co, Fe, Cu, Zr)z Magnets by Prolonging the Drying Time of Ball-Milled Powders

Abstract

Doping of heavy rare Earth elements (HREs) in Sm₂Co₁₇ permanent magnets demonstrates a significant potential for reducing remanence temperature coefficient, thereby improving the precision of magnetic instruments with temperature variation. However, such alloying additions tend to compromise magnetic performance. This study aims to improve the magnetic properties by ball milling process optimization in Sm₂Co₁₇ permanent magnets doped with Dy, Gd, and Er. Prolonging the drying time of ball-milled powders will increase the content of (Sm, Gd)₂O₃, therefore reducing the content of Sm in the matrix and a higher proportion of cell interiors. The increased cell interiors help improve remanence, which is increased from 8.612 to 8.798 kg at room temperature. On the other hand, enriched (Sm, Gd)₂O₃ precipitates may be strong domain pinning sites and are responsible for the coercivity enhancement, which is increased from 15.26 to >26.00 kOe at room temperature. Meanwhile, the thermal stability is also improved by prolonging drying time. The remanence temperature coefficient between $20~^{\circ }$ C and $200~^{\circ }$ C is slightly reduced from −0.0118%/°C to −0.0037%/°C. It is attributed to the increase in the proportion of HREs in the matrix, which is caused by more Sm being consumed by oxidation when compared with heavy rare Earth. This work provides a viable method for magnetic performance enhancement in Sm₂Co₁₇ permanent magnets with HREs doping.