High energy product chemically synthesized exchange coupled NdFeB/α-Fe magnetic powders.

The excellent hard magnetic properties of NdFeB based magnets have an enormous range of technological applications. Exchange-coupled NdFeB/α-Fe magnets were chemically synthesized by a microwave assisted combustion process to produce mixed oxides, followed by a reduction diffusion process to form magnetic nano-composite powder. This synthesis technique offers an inexpensive and facile platform to produce exchange coupled hard magnets. The size dependent magnetic properties were investigated. The formation mechanisms of the oxide powders and the reduction diffusion mechanism were identified. The microwave power was found to play a crucial role in determining the crystallite size. The coercivity of the powder increased with increasing particle size. Room temperature coercivity (H) values greater than 9 kOe and magnetization of 110 emu g was obtained in particles with a mean size of ∼62 nm. An energy product of 5.2 MGOe was obtained, which is the highest reported value for chemically synthesized hard magnetic NdFeB/α-Fe powders.