Neodymium Magnets: Nd-Fe-B Alloy Milled, Pressed in a Field and Sintered (Sagawa 1988)

Neodymium magnets are iron, boron and neodymium. Sagawa's team at Sumitomo melted the three together, ground the casting to a powder finer than 10 µm, lined the grains up in a magnetic field while pressing them, and sintered the compact in argon. Their sample 5, 79 % iron, 6 % boron and 15 % neodymium by atoms, reached 36.5 MGOe, higher than the best samarium-cobalt magnets of the day. Source: M. Sagawa et al. (Sumitomo Special Metals), US 4,770,723 (1988). Unknown: how the pure iron, the ferroboron and the neodymium metal are made; the patent does not say. The magnetising is ours, after Przybylski et al., Sensors 16:569 (2016). The 1 kg weights are our arithmetic from the patent's atomic percentages. Picture: the patent's Fig. 8.