Coercivity enhancement in boron-enriched stoichiometric REFeB melt-spun alloys

Considerable enhancement of magnetic properties was attained in initially stoichiometric nanophase RE12Fe82B6 melt-spun alloys (RE = Nd, Nd + Pr) by means of an excess B content (10 at%) and additions of Zr and Co (2% and 7%, respectively). The intrinsic coercivity exhibited a marked improvement (with respect to the stoichiometric 6 at% B alloy), within the range 50–65%, with a maximum of 1161 ± 14 kA m−1 for the B-rich and Zr-containing alloy, together with an excellent combination of remanence and energy density values of 0.90 ± 0.01 T and 137 ± 4 kJ m−3, respectively. Further Co addition led to a Curie temperature increase, while preserving high coercivity (1176 ± 31 kA m−1) and useful energy densities (119 ± 4 kJ m−3). Results were interpreted on the basis of alloy microstructural features and on variations of the intrinsic magnetic properties, supported by micromagnetic calculations.