Novel microwave assisted chemical synthesis of Nd sub(2)Fe sub(14)B hard magnetic nanoparticles

The high coercivity and excellent energy product of Nd sub(2)Fe sub(14)B hard magnets have led to a large number of high value added industrial applications. Chemical synthesis of Nd sub(2)Fe sub(14)B nanoparticles is challenging due to the large reduction potential of Nd super(3+) and the high tendency for Nd sub(2)Fe sub(14)B oxidation. We report the novel synthesis of Nd sub(2)Fe sub(14)B nanoparticles by a microwave assisted combustion process. The process consisted of Nd-Fe-B mixed oxide preparation by microwave assisted combustion, followed by the reduction of the mixed oxide by CaH sub(2). This combustion process is fast, energy efficient and offers facile elemental substitution. The coercivity of the resulting powders was similar to 8.0 kOe and the saturation magnetization was similar to 40 emu g super(-1). After removal of CaO by washing, saturation magnetization increased and an energy product of 3.57 MGOe was obtained. A range of magnetic properties was obtained by varying the microwave power, reduction temperature and Nd to Fe ratio. A transition from soft to exchange coupled to hard magnetic properties was obtained by varying the composition of Nd sub(x)Fe sub(1-x)B sub(8) (x varies from 7% to 40%). This synthesis procedure offers an inexpensive and facile platform to produce exchange coupled hard magnets.