Large enhancement of GMI effect in polymer composites containing Co-based ferromagnetic microwires

A new kind of composite material consisting of parallel Co-based ferromagnetic microwires embedded in a polymer matrix was designed and produced for high-performance sensor applications. A great enhancement of the giant magnetoimpedance (GMI) effect and its field sensitivity was achieved in these composite materials. It was found that the GMI effect strongly increased with increasing number of ferromagnetic microwires. At a given frequency of 10 MHz, the GMI ratio and its field sensitivity reached the highest values of 450% and 45%/Oe for the composite containing four microwires when compared with those of 14% and 1%/Oe for that containing one microwire. This indicates that the newly developed composite material is very promising for high-performance GMI sensor applications. It was revealed that the increase of the GMI effect in the composite sample was attributed to the decrease of electrical resistance and the increase of effective permeability. An increase of GMI effect with reducing microwire length was also observed and attributed to decrease of the electrical resistance. (c) 2007 Elsevier B.V. All rights reserved.