Simultaneous enhancement of magnetic properties and electric resistance of hot-deformed Nd-Fe-B magnets by doping insulating nano-diamonds

Abstract

The combination of high coercivity and resistivity is a strong requirement for permanent magnets to resist thermal demagnetization under complex operating conditions. However, this still remains a challenge for conventional strategies, which always sacrifice the maximum energy product as the coercivity or resistivity increases. In this work, we report a unique strategy of introducing only 0.1 wt% of insulating nano-diamonds (NDs) into the hot-deformed Nd-Fe-B magnets to significantly and simultaneously improve both magnetic properties (Hci, Br, (BH)max and Hk/Hcj) and resistivity. In particular, the coercivity increased by 60% from 746 to 1193 kA/m. Further microstructure observations indicate that this exceptional effect stems from NDs can effectively inhibit the formation of coarse grains and optimize the distribution of Nd-rich phases, ensuring a strong pinning effect to enhance hard magnetic performance. Meanwhile, the presence of additional grain boundaries and NDs can also lead to higher resistivity by preventing the movement of free electrons. Our work provides a distinctive strategy for interface modification with excellent comprehensive performance in permanent magnets.