Ferromagnetic/antiferromagnetic exchange coupling in melt-spun NdFeB nanocomposites

The effect of Mn addition on the magnetic properties and microstructure of exchange coupled Nd2Fe14B/α-Fe nanocomposites magnets was investigated. The results show that, for nanocomposite NdFeB, the manganese addition can promote crystallization and enhance both coercivity and remanence ratio. Thermomagnetic analysis (TMA) showed that the Mn doping reduces the Curie temperature (Tc) of the Nd2Fe14B phase and raises that of α-Fe phase. Extended X-ray absorption fine structure (EXAFS) shows an increase of disorder degree around Fe atoms with increasing Mn doping content for as-spun samples. Nevertheless, similar to the results of X-ray diffraction (XRD), after annealing, the effect of Mn doping on the EXAFS results almost disappeared. Hysteresis loops after zero-field cooling (ZFC) and field cooling (FC) shows that there is an exchange bias between the Fe–Mn alloy and the magnetic phases. The results of TMA and exchange bias are explained in terms of two roles of the doping Mn element: ferromagnetism at high temperature and antiferromagnetism at low temperature.