Magnetostriction of Fe-rich FeSiB(P)NbCu amorphous and nanocrystalline soft-magnetic alloys

The compositional effect of magneto-elastic and magnetostriction properties of Fe-rich Fe81B15−xPxSi2Nb1Cu1 (ii) Fe82B14−xPxSi2Nb1Cu1 and (iii) Fe83B13−xPxSi2Nb1Cu1 (x = 0, 4, 8) amorphous and annealed nanocrystalline alloy ribbons were investigated. The present study adds knowledge to the limited magnetostriction literature available for Fe-rich nanocrystalline alloys by systematically varying the Fe and P content. A combination of Becker-Kersten and small angle magnetization rotation (SAMR) techniques has been employed for the magnetostriction (λs) evaluation. Both the as-quenched and nanocrystalline ribbons exhibit large positive magnetostriction and show strong compositional dependence to the P content. In the as-quenched condition, 4 at% P addition shows maximum magneto-elastic response and magnetostriction constant, with Fe81B11P4Si2Nb1Cu1 alloy exhibiting a maximum of + 52 ppm and P-free Fe83B13Si2Nb1Cu1 alloy exhibiting a minimum of + 27 ppm. In the nanocrystalline state, a slight reduction of magnetostriction is seen for all alloys, with a maximum of + 32 ppm (4 at% P) and a minimum of + 22 ppm (P-free) in Fe83 at% alloys. The unusual large magnetostriction of optimally annealed samples is attributed to the relatively low crystal volume fraction (30–45%) of nanocrystalline ribbons. The lowest magnetostriction of Fe83B13Si2Nb1Cu1 alloy in both as-quenched and annealed state is explained based on ribbon structural heterogeneity consisting of crystal nuclei and textured α-Fe surface crystallization. The study reveals a contradictory response of magneto-crystal anisotropy (grain size reduction) and magneto-elastic anisotropy to the P addition and ribbon structural heterogeneity. The study discusses the implications of the large magneto-elastic anisotropy associated with Fe-rich nanocrystalline ribbons and the way forward for improving their magnetic softness.