High coercive Zn-bonded Sm-Fe-N magnets prepared using fine Zn particles with low oxygen content

To improve the coercivity of Zn-bonded Sm-Fe-N magnets, fine Zn particles with low oxygen content were fabricated by the hydrogen plasma-metal reaction (HPMR), and Zn-bonded Sm-Fe-N magnets were prepared using the Zn particles. The primary and secondary average Zn particle sizes were 0.23 and 0.93 μm, respectively, and the oxygen content was 0.068 wt%. The oxygen content in the Zn-bonded Sm-Fe-N magnets prepared using the Zn particles also decreased, and the coercivity and energy products of the 15 wt% Zn-bonded Sm-Fe-N magnets were 2.66 MA·m−1 and 53.1 kJ·m−3, respectively, at room temperature. The 10 wt% Zn-bonded Sm-Fe-N magnet was also a high coercivity value of 2.41 MA·m−1, and the energy product was 56.1 kJ·m−3. The coercivity strongly depended on the oxygen content rather than the particle size of Zn, and decreasing the oxygen content in the starting material improved the magnetic properties of Zn-bonded Sm-Fe-N magnets. The coercivity of the 15 wt% Zn magnet measured at 180 and 200 °C was 1.23 and 1.10 MA·m−1, respectively, and the temperature coefficient of coercivity was −0.32%·°C−1.