Improvement of soft magnetic properties of a Fe84Nb7B9 nanocrystalline alloy by synergistic substitution of P and Hf

A strategy of similar elements synergistic substitution was implemented to enhance the amorphous forming ability (AFA), thermal stability, and soft magnetic properties of Fe-Nb-B nanocrystalline alloys. Substitution of B by 2–6 at.% P in a Fe84Nb7B9 alloy increases the AFA and transforms the partially crystallized melt-spun ribbon into a fully amorphous structure. 2–4 at.% P lowers the grain size and enhances the size uniformity and volume fraction of the α-Fe phase in the annealed alloys, thus decreasing coercivity (Hc) from 20.0 to 12.8 A/m and increasing saturation magnetic flux density (Bs) from 1.50 to 1.57 T, whereas 6 at.% P coarsens the α-Fe grains and reduced the magnetic softness. Subsequent replacement of Nb by 2–3.5 at.% Hf increases the thermal stability of a Fe84Nb7B5P4 amorphous alloy, and further refines the α-Fe grains and improves the structural uniformity of the nanocrystalline alloys, thereby enhancing the soft magnetic properties and enlarging optimum annealing temperature window (ΔToa). The Fe84Nb3.5Hf3.5B5P4 nanocrystalline alloy with an average grain size of 9 nm exhibits a low Hc of 11.2 A/m, high Bs of 1.55 T, and wide ΔToa of 90 K. The mechanism of P and Hf substitutions affecting the structure and magnetic properties of the Fe84(Nb, Hf)7(B, P)9 nanocrystalline alloys was discussed in terms of primary crystallization behavior regulation.