GMI Effect in Thin Amorphous Microwires for Sensors and Tuneable Metamateriales Applications

摘要

We present the results on GMI effect in thin microwires at elevated frequencies paying special attention to tailoring the GMI effect and achievement of low hysteretic GMI behavior. We measured magnetic field, H, dependence of real part, Z_1 of the longitudinal wire impedance Z (Z = Z_1 + iZ_2) till 4 GHz in Co-rich microwires. We observed considerable GMI effect at GHz frequencies. General features of these dependences are that the magnetic field of maximum shifts to the higher field region increasing the f. Both ΔZ/Z, and hysteresis loops of nearly-zero Co_(67.1)Fe_(3.8)Ni_(1.4) Si_(14.5)B_(11.5)Mo_(1.7) microwires magnetostrictive exhibit strong sensitivity to the ratio, p, of the metallic nucleus diameter to the total microwire diameter. On the other hand field dependence of the off-diagonal voltage response of nearly zero magnetostriction (λ_s ≈ -3× 10~(-7)) Co_(67.1)Fe_(3.8)Ni_(1.4) Si_(14.5)B_(11.5)Mo_(1.7) with metallic nucleus diameter of 6.0, 7.0 and 8.2 μm exhibits anti-symmetrical shape with almost linear growth within the field range from - H_m to H_m associated with the anisotropy field. Current annealing significantly affects the off-diagonal GMI curves of Co_(67.1)Fe_(3.8)Ni_(1.4) Si_(14.5)B_(11.5)Mo_(1.7) microwires with vanishing magnetostriction constant: under DC current annealing the H_m decreases from 480 A/m in as-cast state to 230 A/m after 5 min annealing with 50 mA current. We found, that if the surface anisotropy is not circumferential, then the magnetization and, consequently, the MI curve Z(H) present hysteresis. This hysteresis can be suppressed by application of sufficiently high DC bias current I_B that creates a circumferential bias field H_B. Applications of thin microwires in tuneable metamaterials are discussed.