Influence of Nb substitution for Fe on the magnetic and magneto-impedance properties of amorphous and annealed Fe76.5−xSi13.5B9Cu1Nbx (x=0–7) ribbons

Abstract

Abstract We report a systematic study of the influence of Nb substitution for Fe on the magnetic properties and magneto-impedance (MI) effect in amorphous and annealed Fe 76.5− x Si 13.5 B 9 Cu 1 Nb x ( x =0, 1, 2, 3, 4, 5, 6, and 7) ribbons. The amorphous ribbons were annealed at different temperatures ranging from 530 to 560 °C in vacuum for different annealing times between 5 and 20 min. We have found that for the as-quenched amorphous ribbons, the substitution of Nb for Fe first increases the saturation magnetization ( M s ) and decreases the coercivity ( H c ) until x =3, for which the largest M s ∼152 emu/g and the smallest H c ∼1.3 Oe are obtained, then an opposite trend is found for x >3. The largest MI ratio (Δ Z / Z ∼38% at f =6 MHz) is achieved in the amorphous ribbon with x =3. A similar trend has been observed for the annealed ribbons. The most desirable magnetic properties ( M s ∼156 emu/g and H c ∼1.8 Oe) and the largest MI ratio (Δ Z / Z ∼221% at f =6 MHz) are achieved for the x =3 sample annealed at 540 °C for 15 min. A correlation between the microstructure, magnetic properties, and MI effect in the annealed ribbons has been established.