Asymmetrical magneto-impedance effect in torsion-annealed Co-rich amorphous wire for MI micro magnetic sensor

An asymmetrical magneto-impedance (MI) effect in almost zero magnetostrictive amorphous wires is obtained using torsion annealing and then magnetizing with a high frequency current biased with a DC current. A highly sensitive MI characteristic showing a field detection sensitivity of more than 100%/Oe was realized in the wire annealed with 450 turn/m torsion at 500/spl deg/C, inducing a spiral anisotropy. The change of the torsion direction from clockwise to anti-clockwise inverts the asymmetrical MI effect. A sensitive linear field sensor is successfully constructed using a pair of the asymmetrical MI heads without bias coils.