Preparation And Magnetic Domain Of Regenerated Re-Fe-B Magnet

Sintered Nd–Fe–B permanent magnets have been popularly used due to their excellentmagnetic properties and a low cost. The increasing demand of magnets has resulted in theenormous production of Nd-Fe-B magnets. At the same time, a great deal of waste is producedin the processes of industrial production, which include breaking raw materials, milling, pressingand machining process. It is necessary to recycle the waste and reduce the manufacturing cost.Therefore, the study of recycling Nd-Fe-B magnet scrap is of considerably practical significance.The aim of previous recycling processes is to purify the rare earth elements via chemical methodfor subsequent re-utilization. However, the recovery ratio of this method is very low, which isharmful to environment.In this work, the waste of sintered Nd-Fe-B magnets was recycled using the method of dopingPrNd nanoparticles. The effect of the nanoparticle doping on the magnetic properties of theregenerated magnet has been studied. As the content of the PrNd nanoparticles increases, thecoercivity increases monotonically. The remanence, the maximum energy product and thedemagnetization curve rectangularity achieve maxima of11.34kGs,31.16MGsOe, and0.951,respectively, for the magnet with4wt%PrNd doping. Microstructural observation shows thatthe major reason of low coercivity is due to the abnormal grain growth caused by the absence ofthe rare earth (Re)-rich phase in the recovery procedure. The appropriate addition of PrNdnanoparticles improves the magnetic properties and refines the grain. The agglomeration of theRe-rich phase, which results from doped PrNd nanoparticles excessively, reduces thecompactness of the sintered regenerate magnets and causes the decrease of remanence.Compared to the magnet with PrNd alloy prepared using the alloy method, the regeneratedmagnet doped with the same amount of PrNd nanoparticles exhibits better magnetic properties and a more homogeneous microstructure. Therefore, it is concluded that PrNd nanoparticledoping is an efficient method for recycling the leftover bits and pieces of Nd-Fe-B magnets.In order to further investigate the mechanism of coercivity enhancement, the Kerr microscopewas used for domain observation in static and dynamic states. Many continuous domains throughthe adjacent grains were observed in the regenerated magnet without PrNd nano-powder, whichwas not a local phenomenon. For the doping with4wt.%PrNd nanoparticles, there were rarelycontinuous domains in the magnet. The reason of the phenmenon was analyzed by domaininvestigation with a pulse field. The effect of Re-rich phase is enhanced by PrNd nano-particledoping, which was studied by analyzing the demagnetizing processes. The uniform distributionof the Re-rich phase exhibits the pinning effect at grain boundaries, thereby improving thecoercivity of the regenerated magnets.