Influence of magnetization processes and device geometry on the GMI effect

In this paper, we review the influence of different geometries (wires, ribbons, films), structures (either homostructures or sandwiches and plated wires), and materials (either amorphous or crystalline) on the giant magnetoimpedance (GMI) effect. The different magnetization processes lead to different limits of this effect. Both analytical and finite-element methods of computation have been used for simulations. Wall movement typically results in larger permeability values and, thus, in better GMI ratios. However, the damping of the walls rapidly reduces the effective permeability. The dynamic equations for magnetization rotation lead to an expression similar to that of Snoek's limit in ferrites, with a permeability drop at high frequency. In conductive/magnetic heterostructures, the resistivity ratio of the two materials is a dominant parameter, and a better performance is found. The model results are also compared with the actual measurements on different materials and geometries and overall agreement is found.