Behavior of sensitivity at edge of thin-film magnetoimpedance element

Hiroaki Kikuchi,Shin Yabukami,Suguru Oe,Hiroaki Uetake

doi:10.1063/1.4972889

Abstract

We fabricated thin-film magnetoimpedance elements in which an impedance of each 100 μm section of element can be examined, to investigate impedance changes of each section subjected to a DC magnetic field. The field strength where the impedance peaks shows a larger value at the edge and it decreases toward the center of the element, while the sensitivity is small at the end of the elements and increases toward the center of the element. The obtained results can be explained on a basis of magnetic field simulation and simple impedance model taking into account a distribution of demagnetizing field. A uniformity of demagnetizing field is significant to obtain a higher sensitivity, and intensity of the demagnetizing field strongly affects a magnetic field strength when the impedance peaks. We also clarified an ellipsoidal shape uniform the distribution of demagnetizing field within the element, which contributes to improve the sensitivity of the MI sensor, especially near edge part.

Highlights

Magnetic field sensor using magnetoimpedance (MI) effect[1] has a high sensitivity at room temperature, and its capability achieves to detect a magnetic field with the order of pico-tesla.[2,3]
We fabricated thin-film sensor elements in which we can evaluate the impedance of 100 μm sections at the edge part of the element, and assessed the impedance changes of each section by applying a DC magnetic field
As the section moves toward center of the element, the impedance changes improve: the peak height increases and the field intensity where the impedance peaks decreases

Summary

INTRODUCTION

Magnetic field sensor using magnetoimpedance (MI) effect[1] has a high sensitivity at room temperature, and its capability achieves to detect a magnetic field with the order of pico-tesla.[2,3] it attracts attention in the biomedical research field[4,5,6] and many researches continue to enhance its sensitivity more. Thin-film MI element[7,8,9,10,11] satisfies such demands, the sensitivity for field detection deteriorates at the end/edge of an element because of the demagnetizing field.[12,13] In particular, near-field detection is important to realize a sensing with higher spatial resolution, solving how to avoid deterioration in the sensitivity of the sensor edge is a mandatory issue; to clarify detailed behaviors of sensitivity at the edge of the element helps us to obtain solutions. Because a rectangular element is the typical shape of sensor elements, on the other hand, we have clarified ellipsoidal elements contribute to improve a uniformity of demagnetizing field.[13] We estimated impedance profiles by taking into account effects of demagnetizing field, and discuss the obtained results on the basis of the estimation

EXPERIMENTAL PROCEDURE

RESULTS AND DISCUSSION

CONCLUSIONS