Induced magnetic anisotropy in Co–Mn–Si–B amorphous microwires

The effect of both thermal treatments as well as chemical etching treatments on the magnetic behavior has been investigated in nearly-zero magnetostriction glass-coated amorphous ${\mathrm{(Co}}_{\text{1−x}}{\mathrm{Mn}}_x{\mathrm{)}}_{\mathrm{75}}{\mathrm{Si}}_{\mathrm{10}}{\mathrm{B}}_{\mathrm{15}}$ $\text{(x=0.08,}$ 0.09, and 0.10) microwires. Such a small change in x results in rather strong changes in the hysteresis loop parameters including coercitivity, $H_c,$ and initial magnetic permeability, ${\mu }_{15}.$ This effect was ascribed to the change of sign of the magnetostriction constant with a proper combination of the coercivity and relatively high initial permeability for the as-cast $\text{x=0.09}$ sample. Thermal treatment (temperatures 100–200 °C for 0.5–2 h) as well as chemical etching in 20% diluted fluoridric acid with duration from 0.5 up to 50 min modify this magnetic parameters owing to the internal stresses relaxation process. In particular, annealing under applied magnetic field (field annealing) can improve more significantly these magnetic parameters: increasing both $H_c$ and ${\mu }_{15}.$ Such phenomenology can be interpreted considering the noticeable longitudinal magnetic anisotropy induced by the combined effects of the magnetic field and strong internal stresses arising from the coating during the thermal treatment. The reduction of the glass coating thickness by chemical etching leads to a decrease of the internal stresses from a coating and, consequently, to a decrease of the transverse magnetoelastic anisotropy. Such decrease of anisotropy plays a role similar to that induced by field annealing on the hysteretic behavior.