Enhanced energy product in magnets intermediate between Nd-Fe-B and ferrite

There is an increasing demand for new hard magnets with reduced content of strategic rare earths because of their high price. The development and optimization of rare-earth free magnets may best be pursued by atomic substitutions in known uniaxial materials with reasonably high Curie temperature (T_c) with a view to reducing materials costs or processability. Fe-doped YCo₅ is promising because it is entirely Tb and Dy free, yttrium is potentially in surplus and a minor amount of cobalt can be replaced with iron to increase the saturation magnetization. Bulk YCo has a strong c-axis uniaxial anisotropy with B_r = 1.06 T, T_c= 6300C, K1= 5.5 MJ/m³, μ₀H_a = 13.0 T and a theoretical maximum energy product (BH)_MAX= 224 kJ/m³ [1]. It has the hexagonal CaCu₅-type structure (space group P6/mmm) with lattice constants a = 4.940 Å and c = 3.981 Å [2]. The best magnetic properties (μ₀H_C = 1.6 T and (BH)_max = 61 kJ/m³) have been reported for conventional dry milled and annealed YCo₄₂₈ [3]. The energy product increases up to (BH)_max= 130 kJ/m³ by mechano-chemical milling with Co, Ca and CaO involving separation of the YCo₅ particles through a cumbersome process [4]. In this work, YCo_5-xFe_x (0 ≤ × ≤ 0.5) alloy powders with higher energy product were prepared by direct ball milling and subsequent annealing.