Magnetoelastic behavior in Co-based glass-covered amorphous wires

The effects of Fe content as well as the dc or ac stress current annealing conditions (current density, annealing time, and tensile stress) on the magnetoelastic behavior of amorphous Co_72.5-xFe_xSi_12.5B₁₅ (x=0, 3, 4.35, 5, and 7. at.%) glass-covered wires have been investigated. The saturation magnetostriction at zero applied stress λ_s (0) in the as-cast state of the samples is about -2.8×10^-6; -0.6×10^-6; -0.11×10^-6; 0.36×10^-6, and 0.9×10^-6 for x=0, 3, 4.35, 5, and 7 at.% Fe, respectively. For nearly zero magnetostrictive amorphous Co_68.15Fe_4.35Si_12.5B₁₅ glass-covered wire, after stress current annealing λ_s (0) changes from small negative to small positive values. The positive λ_s (0) values are obtained after about 3-8 min annealing time for current densities higher than 130×10⁶ A/m². The ac stress current annealing leads to an increase with maximum 60% of the maximum saturation magnetostriction value λ_s (0)_max (depending on the frequency value) in comparison with dc annealing for the same current density, treatment time, and tensile stress. For alloys with x=0, 3, 5, and 7 at.% Fe, after dc or ac stress current annealing with (60-180)×10⁶ A/m², under 300-800 MPa, a modification up to 10% in λ_s (0) values was observed (the absolute value for negative magnetostrictive samples decreases while for positive magnetostrictive samples increases).