Abstract:
The magnetic properties of initial and heat-treated Co$_{69}$Fe$_4$Cr$_4$Si$_{12}$B$_{11}$ microwires in a glass shell with the diameter $D$ = 125 $\mu$m and the diameter of the amorphous metallic core $d$ = 90 $\mu$m produced by the Ulitovsky–Taylor method have been studied. It has been found that the magnetic characteristics, in particular, the saturation field $H_S$ and the coercive force $H_C$ of the samples annealed at a temperature $T <$ 300$^\circ$C do not differ from $H_S$ and $H_C$ of the initial microwire, and those of the samples annealed at $T\ge$ 400$^\circ$C increase by almost one order of magnitude. The obtained experimental data have been explained by the structural features of the microwires. The near-surface values of $H_S$ and $H_C$ at $T <$ 300$^\circ$C are found to be larger than the bulk values by a factor of 5–10. These experimental data have been explained by the existence of structural and chemical ingomogeneities in the near-surface layer, which are inherent in amorphous materials. This difference decreases with a further increase in the annealing temperature, but $H_S$ and $H_C$ increase substantially. This fact has been explained by the beginning of the microwire crystallization.
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