We compared the crystallization behavior and subsequent magnetic properties of α-Fe/Nd2Fe14B-based exchange-spring magnets with and without Nb addition, using differential thermal analysis, X-ray diffraction, transmission electron microscopy, and vibrating sample magnetometer. In the optimally annealed Nd4Fe90Nb2B4 alloy, uniformly distributed α-Fe grains 50-80 nm in diameter are surrounded by Nd2Fe14B1 grains 10-20 nm in diameter as well as by amorphous intergranular layer regions enriched with Nb. The remanence, the coercivity, and the energy product are 1.35 T, 210 kA m-1 (2.65 kOe) and 103 kJ m3, respectively. In the annealed alloy without Nb, the α-Fe and Nd2Fe14B1 phases are brought about from two different intermediate states, resulting in a heterogeneous distribution.
- Crystallization in amorphous system
- Hard-magnetic materials
- Thermal analysis
- Transmission electron microscopy
- X-ray diffraction