Co-Based Amorphous Material for Giant Magneto-Impendance and Fluxgate Sensing Cores

Abstract

Alloy composition (Co94Fe6)72.75Si12.25B13.25Cr1.75 was designed to develop nearly zero-magnetostrictive materials in the form of ribbons and wires to obtain suitable magnetic properties for use as giant magneto-impedance (GMI) and low-noise fluxgate sensor core. During the development of magnetic sensing core using amorphous wires of diameter 80 μm for GMI sensing, we observed a maximum impedance change (GMI ratio) of 430% with as-cast wires which further enhanced to 650% when annealed at 3000C for 5-minutes. The effect of temperature annealing and stress on the magnetic properties of fluxgate sensing core materials has been studied. Magnetic hysteresis loops were measured with 3 mm wide and 45 μm thickness amorphous ribbons on toroidal ring of 50 mm diameter for fluxgate sensor core. A coercivity of 10.57 A/m and saturation field of around 150 A/m was observed with as-quenched ribbon which improved to a coercivity of 2.16 A/m and saturation field about 100 A/m when annealed without stress just above its Curie temperature. An induced anisotropy transverse to excitation direction was achieved by applying temperature with stress and time (3000C/ 100 MPa/ 20-minutes) to use it for fluxgate sensor core.