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.