Theoretical Analysis Of Giant Magneto Impedance Effect In Sandwiched Film

Certain high permeability magnetic materials subjected to an ac current of a sufficiently high frequency can exhibit a sensitive change in impedance in the presence of a dc magnetic field. This effect is called the Giant Magneto Impedance effect (GMI effect).A sandwiched film structure is proposed, which is based on the experimental samples of giant magneto impedance effect. The three-layer sandwiched film, consisting of two metallic ferromagnetic layers separated by a non-magnetic conductive layer. The width of the conductive layer much less than the width of the magnetic layers: a "closed" structure with the magnetic film closing at the edges along the width. Based on the model, the analytical expression of the permeability tensor in multilayered film is deduced with calculating the static and alternate magnetization separately and considering the magnetization mechanisms effect of both the domain movement and the magnetization vector rotation. The impedance is calculated on solving the Maxwell equations for the electromagnetic field and the Landau-Lifshitz equations for the magnetization vector with appropriate boundary conditions at the interfaces between the layers and outer surfaces. The Giant magneto-impedance ratio has a closed relation with the thickness of the constituent thin films, the drive current frequency, the conductivity as well as the anisotropy field. It is shown that the GMI effect is modified by both the magnitude and the orientation of anisotropy field. Then we calculated the impedance in which the anisotropy field is about 3Oe and directing along the easy-axis. The major results obtained are summarized as follows.The maximum impedance change occurs when magnetic field is closed to the effective anisotropy field at high frequencies. The GMI ratio in multilayered film reaches a maximum at frequencies around 1MHz. Larger conductivity of the conducted layer would lead to a larger impedance change ratio in multilayered film. When the thickness of the thin film is fixed, there is an optimum thickness of the conductive layer and the magnetic layers.