Rapid thermal annealing of two-phase nanocrystalline magnet alloys

Nanocrystalline composite magnets consisting both of a magnetically hard phase and a magnetically soft phase show high saturation magnetization, high remanence ratio and large coercivity. The nanostructure depends very much on the processing, treatment used, e.g., conventional rapid annealing (CRA) or flash annealing. In this study, rapid thermal annealing (RTA), commonly used by IC industries, was adopted to anneal various melt-spun Nd-Fe-B flakes, and these flakes and compared to those obtained from CRA. It was found that for the alloys with a higher alpha-Fe fraction, RTA is more capable of attaining, within a heating cycle of less than 200 seconds, superior properties to those from CRA. High resolution TEM study showed that RTA leads to a finer and more uniform nanostructure than those obtained by CRA. The effect of composition on the magnetic properties of RTA treated alloys was also studied. It was concluded that the RTA process has potential for the mass production of nanocomposite alloys.