Co-Based Amorphous Material for Giant Magnetoimpedance and Fluxgate Sensing Cores

Abstract

Soft magnetic materials rich on iron or cobalt have found vast range of usability for sensors such as fluxgates [1] and also, the recently re-invented, magneto-impedance sensors [2]. Giant magneto-impedance (GMI) has experienced huge increase of interest since the late 80's. Although the fluxgate sensor is commercially available, the easy manufacturing of GMI sensors, possibility of miniaturization put attention to many scientists for developing such sensor in many applications. However, GMI sensor has major drawback of large temperature sensitivity [3]. In precise applications, fluxgate sensors are preferred over GMI, which do not saturate the ferromagnetic core and therefore may exhibit perming error. On the other side, the GMI sensors compete with significantly longer period of the development of fluxgates and recently are commercially used for evaluation of microstructural degradation in ferromagnetic materials [4]. Mostly for GMI sensors, amorphous/ nanostructured wires are used rather than ribbons as wire shaped sample has better GMI characteristics than ribbon [5] due to the formation of circumferential anisotropy in wire. On the other hand wires can be used for orthogonal fluxgates but ribbons are preferred over wires for commercial use as they have been tested for last few decades. The magnetization process for the ribbon and the wire shaped samples are assumed to be different presumably due to the difference in cooling process. However, in both cases, the materials should have very low saturation magnetostriction constant and high permeability. The present paper is to understand the variation of sensing properties of the ribbon and wire shaped materials having the same composition, which can be operated both in the GMI and the fluxgate sensing cores and test them in both sensors.