Effect of annealing on magnetic properties of nanocrystalline Hitperm-type glass-coated microwires

• Nanocrystalline structure of as-prepared Hitperm-type microwires.
• Magnetic softening and grain size refinement after annealing.
• Enhancement of domain wall velocity after annealing.
• Change of frequency dependence of switching field after annealing.

We studied magnetic properties of Fe38.5Co38.5B18Mo4Cu1 Hitperm-like glass-coated microwires obtained by Taylor-Ulitovsky technique with nanocrystalline structure consisting of about 20–30 nm BCC α-FeCo and an amorphous precursor in as-prepared samples. We observed a considerable decrease of the average grain size (from about 23 to 11 nm) after annealing. As-prepared and annealed Fe38.5Co38.5B18Mo4Cu1 Hitperm-like glass-coated microwires present rectangular hysteresis loops and fast domain wall propagation. We measured and analyzed the frequency dependence of the switching field dependence and domain wall dynamics in as-prepared and annealed Hitperm-type microwires. Obtained results are discussed in terms of the microstructural relaxation, grains refinement and internal stresses relaxation. An enhancement of the domain wall velocity as well as mobility after annealing has been attributed to the structural relaxation of such grains with positive magnetostriction.

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