Improvement of coercivity thermal stability of sintered 2:17 SmCo permanent magnet by Nd doping

The effects of Nd doping on the microstructures and magnetic properties of Sm _{1– x} Nd _x (Co _0.695Fe _0.2Cu _0.08Zr _0.025) _7.2 ( x = 0, 0.3, 0.5, 0.7, 1.0) permanent magnets are studied. The scanning electron microscope (SEM) analysis of the solid solution states of the magnets shows that with the increase of Nd content, the distribution of elements becomes inhomogeneous and miscellaneous phase will be generated. Positive temperature coefficient of coercivity ( β) appears in each of the samples with x = 0.3, 0.5, and 0.7. The corresponding positive β temperatures are in ranges of about 70 K–170 K, 60 K–260 K, 182 K–490 K for the samples with x = 0.3, 0.5, and 0.7, respectively. Thermomagnetic analysis shows that spin-reorientation-transition (SRT) of the cell boundary phase is responsible for this phenomenon. On the basis of this discovery, the Sm _0.7Nd _0.3 (Co _0.695Fe _0.2Cu _0.08Zr _0.025) _7.2 magnet possessing thermal stability with β ≈ –0.002 %/K at the temperature in a range of 150 K–200 K is obtained.