Maximum MI Research Articles

Magneto-impedance effect in Co-based metallic glass ribbons

In this paper we report on measurements of the MI effect in some Co-based commercial ribbons. The impedance of the amorphous ribbons is found to be a very strong function of the drive current frequency. It is also observed that at frequencies higher than 100 kHz, this response becomes sensitive to the application of a dc magnetic field that leads to a maximum value for the MI effect at an applied dc magnetic field higher than the saturation magnetic field of the samples. At frequencies above 100 kHz, the transverse ac field interacts with the longitudinal dc field due to the movement or realignment of the magnetic domains. Thus, the dc magnetic field modifies the ac permeability of the ribbon. Since amorphous ferromagnetic ribbons show nonlinear relationship between the applied dc magnetic field and the magnetic induction, the ac permeability does not change linearly with the applied dc magnetic field. The impedance of the ribbon strongly depends on the coupling of ac field with transverse domains and shows nonlinear relationship with dc magnetic field. It is also observed that the maximum MI ratio varies strongly with the frequency and with the amplitude of the ac drive current.

Magnetoimpedance of NiFe/Ag multilayers in the 100kHz–1.8GHz range

Abstract Magnetoimpedance curves at frequencies up to 1.8 GHz for (Ni 81 Fe 19 /Ag) n multilayers with n =15, 50 and 100, and thickness ratio t Py / t Ag : 100 7 , 100 25 , 100 100 , 200 14 , 200 50 and 200 200 A are presented. Evidences of FMR are observed in most samples studied. Samples with 15, 50 and 100 bilayers exhibited a maximum MI ratio of about 100%, 175% and 250%, respectively. For samples with t Py =4t Ag , peculiar impedance spectra with 4 peaks were observed.

The coercivity dependence of giant magneto-impedance effect in Fe–Cu–Nb–Si–B based metallic alloy ribbon at different crystalline stages

We have studied the giant magneto-impedance (GMI) effect in one Fe-based FINEMET alloy ribbon with nominal composition Fe73.5Cu1Nb3Si13.5B9 (at %). DTA experiments were conducted to identify the primary and secondary crystallization temperatures. XRD, SEM and EDAX were performed to identify the phases at various crystalline stages. Static magnetic properties of the ribbons were measured using a VSM. Coercivity was found to be a strong function of annealing temperature, and this, in turn depended on the size and type of the crystalline phases. The maximum MI effect of 103.4% was observed at annealing temperature of 600°C. It was found that a small change in DC coercivity as a result of annealing greatly changed the MI ratios of the crystalline ribbons. Annealing above the secondary crystallization temperature caused the precipitation of Fe2B and Fe3B phases, which induced magnetic hardening and eliminates MI sensitivity.

Magnetoimpedance of sandwiched films: experimental results and numerical calculations

The magnetoimpedance effect (MI) is studied in FeNi/Cu/FeNi and FeNi/Si/Cu/Si/FeNi sandwiches with different widths of a central Cu layer in the frequency range of 0.1–150 MHz. A maximum MI of about 8% was obtained. A weak dependence of the MI on the amplitude of the AC indicates almost linear MI behavior. The results of finite elements method numerical calculations are compared with the experiments, showing it is a powerful tool to predict the MI behavior.

Giant magneto-impedance effect in nanocrystalline ribbons

Results on the GMI response of Fe 73.5Cu 1Nb 3S 13.5B 9, Fe 90Hf 7B 3,and Fe 90Zr 7B 3 nanocrystalline ribbons are reported. The obtained results are compared with those obtained for CoFeSiB amorphous ribbons, using the MI ratio, defined as ΔZ Z = [Z(H dc = 0)−2(H dc = 1 kA·m −1)] Z(H dc = 0) . The most sensitive GMI response is given by Fe 90Zr 7B 3 nanocrystalline ribbons — about 30%. A sensitivity of about 25% has been observed in Fe 90Hf 7B 3 nanocrystalline ribbons, which is comparable to that of CoFeSiB amorphous ones, while for Fe 73.5Cu 1Nb 3Si 13.5B 9 ones, the maximum MI ratio reaches only 10%. The results are explained in terms of differences in the electrical resistivities of the samples investigated, as well as by taking into account the local anisotropy distributions in each case. One of the main goals of this paper is to discuss the role of good soft magnetic properties on the magnitude and sensitivity of the GMI effect.