Annealing induced evolution of structure and high frequency magnetic properties in nanocrystalline glass-coated microwires

The annealing induced evolution of structure and magnetic properties of glass-coated microwires (GMW) made of FeNbCuBSi alloy were studied. The microwires were produced by a modified Taylor method. The annealing temperatures were varied from 800 to 890 K. In their as-cast state, all microwires featured perfect square hysteresis loops. After annealing, the GMW hysteresis loop width decreased thus indicating the alloy devitrification and the nanocrystalline phase growth. The grain size measured in TEM studies was 10–15 nm. The hysteresis loops of GMW with 13% Si content remained square-shaped in the whole range of annealing temperatures, while in the case of GMW with 16% Si content, increasing Ta caused the loop transformation to a flat, anhysteretic one. After the hysteresis loop underwent the square-to-flat transformation, an enhancement in GMW high frequency properties had been observed.