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 M_r/ M_s values for melt-spun Nd ₄Fe _7.35Co ₃(Hf _{1- x}Ga _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- x}Ga _x)B _18.5 alloys) which is discussed in terms of previously simulated exchange coupling parameters.