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

TL;DR

This study investigates how the metal-to-wire diameter ratio affects high-frequency magnetoimpedance in glass-coated CoFeBSi microwires, revealing peak impedance behaviors and resonance phenomena linked to magnetic anisotropy and shell magnetization.

Contribution

It provides new insights into the influence of the diameter ratio on MI and anisotropy fields using a thermodynamic and rotation model analysis.

Findings

Maximum normalized impedance varies with frequency and diameter ratio.

Resonance in impedance components depends on the DC magnetic field.

The behavior is explained by a shell magnetization rotation model.

Abstract

High frequency [1-500 MHz] measurements of the magnetoimpedance (MI) of glass-coated Co$_{69.4}$Fe$_{3.7}$B$_{15.9}$Si$_{11}$ microwires are carried out with various metal-to-wire diameter ratios. A twin-peak, anhysteretic behaviour is observed as a function of magnetic field. A maximum in the normalized impedance, $\Delta Z$/$Z$, appears at different values of the frequency $f$, 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 our results with a thermodynamic model that leads to a clearer view of the effects of $p$ on the maximum value of MI and the anisotropy field. The behavior of the real and imaginary components of impedance is also investigated; they display a resonance that becomes a function of the DC field $H_{DC}$ for values larger or equal to $H_{K}$ the circumferential anisotropy field for each $p $ value. These results are interpreted in terms of a rotation model of the outer shell magnetization.