The effect of magnetic field treatment on the enhanced exchange coupling of a Nd 2Fe 14B/Fe 3B magnet
An externally applied magnetic field during heat treating a Nd 2Fe 14B/Fe 3B based spring magnet was found to enhance the exchange coupling between the hard and soft magnetic grains. A > 30% increase in Mr/ Ms values for melt-spun Nd 4Fe 7.35Co 3(Hf 1- xGa x)B 18.5 ( x = 0. 0.5, 1) alloys resulted from a uniform distribution of Fe 3B, α-Fe and Nd 2Fe 14B phases, and a 20% increase from a reduced grain size of those phases. The externally applied magnetic field induced a uniform distribution of fine grains. The present study also shows that there is an optimum grain size exhibiting a high coercivity (22 nm for Nd 4Fe 73.5Co 3(Hf 1- xGa x)B 18.5 alloys) which is discussed in terms of previously simulated exchange coupling parameters.