Phase composition and magnetic properties of SmCo5/Fe nanocomposite powder prepared by cryomilling

Ball milling temperature is a significant factor influencing the phase composition and magnetic properties of ball-milled powders. We compare the morphology, phase composition and magnetic properties of SmCo₅ and SmCo₅/Fe powders produced through cryomilling and conventional milling techniques. Our findings indicate that cryomilling effectively inhibits cold welding and phase transformations, reduces contamination, and enhances the magnetic properties of powders compared with conventional ball milling. Larger sized particles formed due to cold welding were observed in conventional milled powders, while better dispersion was observed in cryomilled powders. Sm₂Co₁₇ phase appeared in the SmCo₅ powder after 12 h of conventional ball milling, while only an amorphous phase was found in the cryomilled one. When ball milling time was extended from 2 h to 12 h, the Fe content in the conventional milled SmCo₅ powder increased from 4.6 wt% to 7.9 wt%, which was much higher than that in the cryomilled SmCo₅ powder (from 1.4 wt% to 2.2 wt%). After 8 h of ball milling, the coercivity of the cryomilled SmCo₅ powder reached 3.01 kOe, representing a 64.48 % increase compared with that of the conventional milled powder. The saturation magnetization of cryomilled SmCo₅/Fe composite powder was 122.89 emu/g, which is 4.34 % higher than that of the conventional milling. As the annealing temperature increases from 500 °C to 700 °C, the main phase of the hard magnetic phase in the SmCo₅/Fe nanocomposite powders transformed from SmCo₃ phase to Sm₂Co₁₇ phase, and the content of the soft magnetic Fe(Co) phase is decreasing, and the coercivity is increasing. SmCo₅/Fe cryomilled magnetic powder annealed at 550 °C possesses a M_r of 79.63 emu/g, a M_r/M_s of 0.71, a H_c of 6.16 kOe, which are much higher than that of the conventional milled SmCo₅/Fe powder annealed at 550 °C. This work provides a ball milling process optimization strategy for the preparation of high performance nanocomposite magnets.