Magnetostriction of amorphous Co-based and Fe-Ni-based magnetic microwires: Effect of stresses and annealing

The magnetostriction coefficient and its stress dependence are evaluated in Co- and Fe-Ni- based glass-coated microwires with different character of hysteresis loops. The hysteresis loops as well as the magnetostriction coefficients of the microwires depend mostly on the chemical composition of the metallic nucleus. We found that the stress dependence of the magnetostricition coefficient, λs, is linear for both families of studied microwires, however a decrease with applied stress is observed for Co-rich microwires with negative magnetostriction coefficient. In contrast, a linear increase of the magnetostriction coefficient with applied stress is observed for Fe-Ni rich microwires with positive magnetostriction coefficient. Additionally the λs - value is affected by annealing. We evaluated the dependence of λs on annealing time, tann, for different annealing temperatures. In Co-rich microwires a change of the λs sign is observed. For both kinds of microwires (either with positive or with negative λs) λs(tann) at Tann = 400 °C present similar features: an increase with tann up to tann ≈ 10 min followed by a decrease for tann> 10 min. The λs(tann) dependencies are affected by the annealing temperature. Observed results are discussed in terms of influence of internal stresses and short range ordering induced by annealing.