Grain size refinement in nanocrystalline Hitperm-type glass-coated microwires

• Grains size refinement upon annealing.
• Enhancement of the domain wall velocity as well as mobility after annealing.
• Nanocrystalline structure in as-prepared microwires.

We present a new-Fe38.5Co38.5B18Mo4Cu1 Hitperm glass-coated microwires obtained by Taylor-Ulitovsky technique with nanocrystalline structure consisting of about 23 nm of BCC α-FeCo and an amorphous precursors in as-prepared samples. Annealing resulted in a considerable decrease of such nano-grains down to (11 nm). Obtained results are discussed in terms of the stress diffusion of limited crystalline growth and the chemical composition. Rectangular hysteresis loops have been observed on all annealed samples that are necessary conditions to obtain fast domain wall propagation. An enhancement of the domain wall velocity as well as mobility after annealing has been obtained due to the structural relaxation of such grains with positive magnetostriction. These structure benefits found in the nanocrystalline Hitperm glass-coated microwires are promising for developing optimal magnetic properties.