Effect of annealing on the head-to-head and tail-to-tail domain wall potentials in bistable microwires

We examined how thermal and mechanical treatments reshape the domain wall potential in Fe76Si9B10P5 glass-coated bistable microwires by separately tracking head-to-head and tail-to-tail domain wall switching fields. Stepwise furnace annealing between 200 and 350 °C and a subsequent 100 MPa tensile-loading / unloading (tensile training) cycle, designed to induce additional stress relaxation, were performed. After each step, changes in the domain wall potential were inferred from the switching-field distribution. Annealing lowers the switching field overall but with polarity-dependent, non-monotonic trends: the head-to-head and tail-to-tail domain wall potentials display distinct temperature dependences with partial convergence near 250 °C, where their switching field distributions are most similar in width, yet their mid- to low-field regions still differ, revealing dissimilar potential shapes. Across all conditions, the high-field tails overlap and the fitted high-field slope varies only weakly with temperature, indicating that short-range (atomic-scale) pinning remains essentially unchanged while the observed evolution arises from the magnetoelastic contribution. The fluctuations of the switching field remain small (~0.4–0.6% of the maximum switching field) and narrow with annealing in a polarity-dependent way (different for head-to-head and tail-to-tail domain wall potentials). Tensile training further homogenizes the head-to-head and tail-to-tail domain wall potentials at zero load, which indicates that the loading–unloading sequence introduced additional irreversible stress relaxation. These findings show that controlled annealing and tensile training can tailor the domain wall potential to improve precision and reproducibility in magnetic microwire sensors.