Annealing Effect on Domain Wall Dynamics in Wires With Induced Gradient of Perpendicular Anisotropy

Amorphous glass-coated Fe-Si-B-P microwires with an induced gradient of perpendicular magnetic anisotropy are studied. The angular dependence of the domain wall mobility in the perpendicular magnetic field is present in as-cast sample. After thermal annealing below the crystallization temperature, the effect of the perpendicular magnetic field is suppressed due to the relaxation of internal mechanical stresses. Moreover, the domain wall mobility decreases, and the critical field increases. The results are explained in terms of the release of mechanical stresses induced during production after annealing. Furthermore, a new mechanical stress distribution is induced due to the slow cooling rate after thermal annealing. Scanning electron microscopy images of annealed samples below and above the crystallization temperature suggest the presence of the gradient of perpendicular magnetic anisotropy. Directional growth of the crystals after annealing above the crystallization temperature follows the induced stresses and shell-like structure in the cross section is recognized.