Giant magneto-impedance in heterogeneous microwires

Recent results concerning the giant magneto-impedance effect, GMI, in magne tic microwires having diameter in the range of a few micrometers and hetero geneous character are introduced in this work. Two types of microwires have been studied, namely, (i) magnetic microwires covered by insulating Pyrex glass coating and (ii) copper wires covered by electrodeposited magnetic mi crotubes. The magnetic anisotropy distribution in each type of microwire is correlated with giant magneto-impedance. While the main source of anisotro py in glass coated microwires is of magnetoelastic origin created by the st resses induced during quenching and by the coating, in the case of the micr otubes the origin is the columnar growth during the electrodeposition. The influence on GMI of various treatments that modify the anisotropy is analyz ed. Heterogeneous microwires with different thicknesses of insulating coati ng and of magnetic tube are analyzed. (C) 2000 American Institute of Physic s. [S0021-8979(00)04024-X].