Anisotropic $ {\alpha } $ -Fe/Nd–Fe–B Exchange-Spring Magnets Produced by High-Pressure Crystallization

A series of Nd–Fe–B + $\alpha $ -Fe nanocomposites was prepared by pressure crystallization of quasi-amorphous rare-earth lean precursors. The crystallization temperature of Nd 2 Fe 14 B was determined to be 560 °C. Fully dense compacts crystallized under the pressures of up to 1 GPa exhibited a fully exchange coupled behavior with coercivities ranging from 1.98 to 2.5 kOe, depending on the Nd content. The evolution of coercivity as a function of pressure crystallization time indicated slower crystallization/growth kinetics compared with the ribbons crystallized under atmospheric pressure. All crystallization took place within 5 min and optimum coercivities were obtained after 20 min of holding time. Both the X-ray diffraction and magnetic measurement $M(H)$ results indicated the presence of a crystalline texture. Microstructural characterizations by a transmission electron microscope revealed a layered structure composed of alternating layers of Nd 2 Fe 14 B and $\alpha $ -Fe.