EFFECT OF ANNEALING ON THE GIANT MAGNETO-IMPEDANCE OF CO-BASED WIRES

The giant magnetoimpedance (GMI) effect in Co75Fe4.2Si8B12Nb0.8 melt extraction wires annealed in a vacuum furnace at 450°C holding for 10min, 20min, 25min, 30min and 40min, respectively, is investigated. Strong GMI effect is observed at a typical frequency of 37MHz. The observation on the GMI effect indicates that the anisotropy field dominated by the anneal treatment is vital to the GMI ratio △Z/Z(%) and its field sensitivity. The improvement on GMI effect when anneal time is less than 20min is ascribed to the stress release, decreased anisotropy field and increased permeability. The decrease of GMI effect when anneal time is over 25min results from nanocrystalline phase grow up inducing the crystalline anisotropy field increase. Suitable annealed wires possess large GMI ratio (855%) and little anisotropy field achieving high field sensitivity to 151%/Oe. These results indicate these Co-based melt extraction wires are excellent for using in novel field sensors applications.