Magnetic and microstructural properties of sintered FeNdB-based magnets with Ga and Nb additions

Sintered magnets based on the Fe14Nd2B phase were prepared by alloying the additive elements Ga and Nb, which mainly influence the microstructure and not the intrinsic magnetic properties. The room-temperature permanent magnetic properties are the intrinsic coercivity, μ0Hc = 1.70 T and the remanent polarization, Jr = 1.20 T. From the temperature dependence of the coercive field the microstructural parameters αK and Neff were determined. Furthermore, the Kerr microscopy was used to investigate the domain patterns and the microstructure. Phase analyses showed that the low-melting element Ga forms new intergranular phases and the refractory metal Nb forms high-melting borides in the intergranular phases and small precipitates in the hard magnetic grains.