THE INFLUENCE OF GA-SUBSTITUTION ON THE COERCIVITY OF ND-(FE,CO)-B SINTERED PERMANENT-MAGNETS

In Co-substituted NdFeB sintered magnets several additional phases such as Nd(Fe, CO)yB? with y = 2, 3 and 4 are found besides the hard magnetic phase and the Nd-rich intergranular phase. The low coercivity of the magnet is attributed to the occurrence of these soft ferromagnetic phases. In Ga-doped Nd-(Fe, Co)-B sintered magnets new intergranular phases, such as Nd(Ga, Fe, Co) and Nd(Ga, Fe, Co)2 are found instead of the soft ferromagnetic Co-rich phases. From X-ray microanalysis data it is concluded that Ga substitutes the transition metal atoms in the 2:14:1-phase and Ga is not detected in the Nd-rich phase at all. The increase of the coercivity of Ga-doped magnets is correlated to a higher volume fraction of intergranular phases and an increased wetting during sintering due to these phases. © 1990 IEEE