Improvement of soft magnetic properties by simultaneous addition of P and Cu for nanocrystalline FeNbB alloys

The additional effect of P and/or Cu on the structure and the magnetic properties of Fe–Nb–B nanocrystalline soft magnetic alloy tapes with a wide width of 5mm produced in air was investigated. Although Cu or P addition changes the magnetic softness a little, only the simultaneous addition of 1at.% P and 0.1at.% Cu significantly improves the soft magnetic properties of the crystallized alloys. The best magnetic properties (higher permeability than 45×103, lower coercivity than 5A∕m, and saturation magnetic flux density of 1.50–1.54T) were obtained in the compositional ranges of 6.6–6.8at.% Nb and 8.4–8.8at.% B with 1% P and 0.1% Cu, and these values are superior to the typical nanocrystallized Fe84Nb7B9 alloy prepared in a vacuum. The improvement probably originates from the decrease in the distribution of the α-Fe grain size in the crystallized structure by the simultaneous addition.