Incident Power Influence on Magnetoimpedance Element With Domain-Wall Resonance

Abstract

Magnetoimpedance(MI) sensor utilizes permeability changes of the material through skin effect and ferromagnetic resonance when the sensor is applied to a magnetic field, and it has a higher sensitivity [1]. The sensors, which are composed of amorphous wires, are currently commercialized as compasses in mobile phones, and researches advance their sensitivity still continue for application of biomedical research [2] and nondestructive testing [3]. On the other hand, thin-film MI elements which has the compatibility with miniaturized integrated electronic devices such as driving and detecting circuits, contributes to the miniaturization of sensor device with higher spatial resolution. However, one problem of using thinfilm elements is higher operating frequency. Typically, operating frequency is above 100 MHz to GHz range for elements with several μm thickness; this is unsuitable for general-purpose driving and detecting circuits, which normally operate below 20–30 MHz. During our investigations about thinfilm MI elements, we found an interesting behavior that the frequency profile of impedance shows double peak depending on the applied bias field, that is, another peak appears at lower frequency region [4]. Then we analyzed this profile based on the domain wall equation and indicated the changes in impedance is attributed to the domain wall resonance (DWR) [5]. We also showed a potential of the phenomenon applied for developing a highly sensitive sensor operated at frequencies around the dozen megahertz region. In such cases, more detailed investigations about incident power is required because the behavior of impedance changes strongly depends on input high frequency power and this behavior is not still clear. Thus, in this study, we evaluated experimentally the impedance profile around frequency where the DWR occurs when the incident ac power modulated, and discussed about the sensitivity of impedance changes.