Improvement of stepped magnetoimpedance properties by controlling demagnetizing effect

Magnetoimpedance (MI) element is used for compasses in mobile phones [1], and its application expands to various industrial fields such as biomedical field and nondestructive testing because of its higher sensitivity [2]. On the other hand, MI element with a stepped impedance properties was obtained from the rectangular amorphous film with a uniaxial easy axis at an inclined angle relative to the width of the element [3] as a new feature of this sensor. This element is expected to apply for a novel magnetic field sensor for detection of a threshold field, with a memory function, etc. Additionally, a demand for a miniaturization of MI elements increases on the miniaturization of electronic devices and the progress in fast signal processing. Thus, an MI element fabricated using a thin film is a prospective candidate because this configuration is compatible with integrated electronic devices. However, when a thin-film MI sensor is miniaturized, decrease in the properties due to a demagnetizing field is unavoidable. Therefore, we clarified that the deterioration of the properties at the edge of the elements can be mainly attributed to the distribution of the demagnetizing field and suggested that only the central regions of an element should be utilized for sensing applications to eliminate the adverse effect due to the distribution of demagnetizing field [4]. However, controlling the distribution of demagnetizing field in the element contributes to the miniaturization of the sensor devices more. Thus, in this study, we prepared MI sensor elements in which the sensor shapes have a typical rectangular and a quasi-ellipsoidal shape for avoiding the demagnetizing field distribution. Then the impedance measured and domain observations were experimentally performed using prepared MI elements and we investigated the usefulness of the controlling of demagnetizing field distribution in the elements.