New nanocrystalline high-remanence Nd-Fe-B alloys by rapid solidification

A new type of permanent magnet alloy based on Nd-Fe-B, containing 8–9 at% Nd and processed by melt spinning, is described. Remanences of greater than 1 T are obtained in isotropic ribbon samples, with energy products, (BH)max in excess of 160 kJ m−3 and intrinsic coercivity up to about 485 kA m−1. Microstructurally, the alloys consist of two phase, a matrix of magnetically hard Nd2Fe14B with numerous particles of α-iron on grain boundaries. Both the mean grain size of the Nd2Fe14B ( < 30 nm) and the mean particle size of the α-iron ( < 10 nm) are ultra fine. The second quadrant of the J-H loop is typical of a single-phase, magnetically hard material. The relationship between magnetic properties and microstructure in these nanocrystalline two-phase alloys is discussed.