Improvement of thermal stability of Nd-Dy-Fe-Co-B sintered magnets by additions of Al, Nd and Ga

To improve the thermal stability of (Nd 0.8 Dy 0.2 ) (Fe 0.86 Co 0.06 B 0.08 )5.5 sintered magnets for heavy duty applications, such as starter motors, effects of additional elements(M=Al, Nb and Ga) On the thermal stability were investigated in the (Nd 0.8 Dy 0.2 ) (Fe 0.86-u -Co 0.06 B 0.08 M u )5.5 sintered magnets. The addition of Al increased i H c , but did not decreased irreversible losses at 220°C(Pc= 2). The sintered magnet with M=Nb and u=0.006 had lower i H c and higher irreversible losses than u=0, while the sintered magnet with M=Nb and u=0.015 had higher i H c and lower irreversible losses. Additions of Ga were resulted in higher i H c and lower irreversible losses. A combination of both Nb and Ga additions was also studied and a very low irreversible loss of under 5 % after exposure at 260°C(Pc= 2) was obtained for (Nd 0.8 Dy 0.2 ) (Fe 0.835 Co 0.06 B 0.08 Nb 0.015 Ga 0.01 )5.5 sintered magnets. The obtained magnetic properties for the magnet are B r =10450 G, b H c =10000 Oe, i H c =27100 Oe and (BH)_{\max}=26.2 MGOe.