Effect of super heat treatment on crystallization behavior and magnetic properties of Nd4.5Fe77B18.5 nanocomposites

Melt-spun Nd4.5Fe77B18.5 ribbons were prepared under various superheat temperatures. The microstructure characteristics, crystallization behavior, and subsequent magnetic properties of Fe3B/Nd2Fe14B nanocomposite magnets were investigated using X-ray diffraction, differential thermal analysis, and vibrating sample magnetometry. It was shown that melt spinning at different quenching temperatures caused the as-quenched ribbons to have distinctive crystallization behavior. Depending on superheat temperature, phase transformation of the ribbons during annealing may take place in one of the following sequences: (1) amorphous phase (Am)→Am'+Fe3B→Fe3B+ Nd2Fe23B3→ Fe3B+Nd2Fe14B, or (2) amorphous phase(Am)→Am'+Fe3B→Fe3B+Nd2Fe14B. For the latter, the ribbon after optimal annealing exhibited single-phase magnetic behavior. In the first case, magnetic properties of the optimally heat treated ribbons deteriorated and an apparent kink could be seen along the demagnetization curves near the zero field.