Effect of the metal-to-wire ratio on the high-frequency magnetoimpedance of glass-coated CoFeBSi amorphous microwires

摘要

High frequency [1-500 MHz] measurements of the magnetoimpedance (MI) ofglass-coated Co$_{69.4}$Fe$_{3.7}$B$_{15.9}$Si$_{11}$ microwires are carriedout with various metal-to-wire diameter ratios. A twin-peak, anhystereticbehaviour is observed as a function of magnetic field. A maximum in thenormalized impedance, $Delta Z$/$Z$, appears at different values of thefrequency $f$, 125, 140 and 85 MHz with the corresponding diameter ratio $p$ =0.80, 0.55 and 0.32. We describe the measurement technique and interpret ourresults with a thermodynamic model that leads to a clearer view of the effectsof $p$ on the maximum value of MI and the anisotropy field. The behavior of thereal and imaginary components of impedance is also investigated; they display aresonance that becomes a function of the DC field $H_{DC}$ for values larger orequal to $H_{K}$ the circumferential anisotropy field for each $p $ value.These results are interpreted in terms of a rotation model of the outer shellmagnetization.