Effects of Cu content on magnetic properties of nanocrystalline Fe–Cu–Nb–Si–B alloy ribbons

Nanocrystalline Fe_74·29–xCu_xNb_2·9Si_13·56B_9·25 (x = 0·8–1·1) alloy ribbon cores were prepared by the single roller melt spinning technology and the subsequent annealing treatment. The Cu content dependences of the thermal stability, crystallisation behaviour, and soft magnetic properties of Fe_74·29–xCu_xNb_2·9Si_13·56B_9·25 alloys were investigated. The alloy's coercivity H_c firstly increased and then decreased with increasing Cu content from 0·8 to 1·1, while the saturation induction B_s and the effective permeability μ_e showed the opposite variation tendencies. The alloy with the Cu content of 0·9, which had the minimum H_c of 0·59 A m⁻¹, the maximum B_s of 1·26T and the maximum μ_e of 120800, was found to exhibit the relatively best soft magnetic properties. When the Cu content was more than 0·9, the soft magnetic properties deteriorated obviously. This is due to the growth of the alloy's nanograins caused by the increase in the Cu content and suggests that the proper Cu content is effective to improve the soft magnetic properties.