Theoretical Study Of The Giant Magneto-impedance Effect In Soft Magnetic Thin Films

Giant magneto-impedance (GMI) effect is the phenomenon that the impedance of ferromagnet can be dramatically changed by the applied static magnetic field. Sensors made by giant magneto-impedance materials can meet the demands of high sensitivity, micro-size, quick response, low power consuming, no contact detecting and no hysteresis. Furthermore, this kind of sensors are driven by AC current, so that one can easily realize many functions in using them, such as modulating, demodulating, filtering of the wave, oscillation and resonance. Because of the great application potential in the fields of engineering, GMI effect has been researched in wire, ribbon and film of soft magnetic materials, while thin film sensors are advantageous on mass-production integration circuit using semiconductor, etc, so it is highly valuable to study the GMI effect in soft magnetic film materials.A model of Giant Magneto- Impedance (GMI) effect for sandwich structure films consisted of two soft magnetic layers and an inner nonmagnetic metal layer was proposed, the GMI effect was investigated theoretically. In the model, the dynamic component of magnetic anisotropy field was considered. The main results were as follows:1. A model was proposed for a sandwich-structured film with a transverse anisotropy, and thus a 180°magnetic domain structure. The Maxwell equations were solved under certain boundary conditions, and the expressions of distributing of AC current in the soft magnetic layers and inner metal layer were derived. The AC impedance was then calculated by definition.2. We used Landau-Lifshitz equation to describe the motion of the magnetization under the external magnetic field, solved the equation to obtain the magnetic permeability tensor. In this calculation, the dynamic part of anisotropy field depending on the AC current was considered. We got the expression of effective permeability at last.