Enhancement of impedance change at low frequency in a thin-film magnetoimpedance element

In this paper, we found an atypical profile on the frequency dependence of a thin-film magnetoimpedance element having a narrow width and a thickness of several microns in the lower frequency region, although a typical magnetoimpedance shows a single peak above the 100 MHz region. The observed peak achieves higher intensity and frequency with increasing applied bias DC magnetic field, and disappears at the higher applied field. Since the sensitivity of the element for the applied magnetic field maintains nearly the same level as that in the high frequency region, the existence of the peak in the low frequency region brings us a possibility to realize a thin-film magnetic field sensor with higher sensitivity operating in the low frequency region. We confirmed experimentally that the enhancement of impedance change in low frequency is attributed to a large permeability change in the low frequency region, which may contribute to the domain wall resonance.