Giant magnetoimpedance and stress-impedance effects in multilayered FeSiB/Cu/FeSiB films with a meander structure
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Giant magnetoimpedance (GMI) and giant stress-impedence (GSI) effects were realized in multilayered FeSiB/Cu/FeSiB films with a meander structure by magnetron sputtering on thin glass substrates. The GMI and GSI effects were studied in the frequency range of 1–40 MHz for the multilayered FeSiB/Cu/FeSiB films. Experimental results show that a large negative GMI ratio of −23% is obtained at Ha ⳱ 12 kA/m for a frequency of 20 MHz. The GSI ratio is −20% for a frequency of 1 MHz with the deflection of 150 m of the multilayered FeSiB/Cu/FeSiB films. The GSI effect is attractive for stress or pressure sensor applications.
I. INTRODUCTION
II. EXPERIMENTAL
The giant magnetoimpedance (GMI) effect has been extensively studied in the past few years in amorphous soft ferromagnetic wires and ribbons due to their potential applications in magnetic field sensing and magnetic recording heads. However, many device applications still require materials in thin-film form, and a large GMI effect has been observed in soft ferromagnetic films and sandwiched and multilayered films.1–3 In particular, the large GMI effect can be observed in sandwiched and multilayered films at a frequency below 20 MHz, which is very attractive for magnetic field sensors. In addition, a force or pressure applied to the soft magnetic materials causes a change in magnetic properties such as the hysteresis loop, magnetic permeability, and magnetic anisotropy; this results in a large change of impedance of the soft magnetic materials, which is called the giant stressimpedance (GSI) effect. In 1997, the GSI effect was reported by Shen et al.4 in negative magnetostrictive Cobased amorphous wire, where a GSI ratio of 14% was obtained for a frequency of 20 MHz with tensile stress of 14 MPa. The strain gauge factor was 1200, which is six times larger than that of the silicon strain gauge. Later, stress sensors based on the GSI effect in amorphous soft magnetic wires were constructed.5,6 However, only a few results concerning the GSI effect have been reported in the soft magnetic films or multilayered films.7 Here we present our studies on the GMI and GSI effects in multilayered FeSiB/Cu/FeSiB films with a meander structure, where the amorphous soft FeSiB film has a large positive magnetostriction.
The film structure of the multilayered FeSiB/Cu/ FeSiB films with a meander structure is shown in Fig. 1; the top view is shown in Fig. 1(a) and the cross section of the multilayered FeSiB/Cu/FeSiB films is in Fig. 1(b). The multilayered films are composed of an inner Cu layer and two outer ferromagnetic FeSiB layers with extended multilayered film electrodes. The width and length of the multilayered FeSiB/Cu/FeSiB films are the same except for the difference in film thickness. The width of the Cu layer and FeSiB films is 1 mm, and the length of the layered films is shown in Fig. 1(a). The space between two meander lines of the multilayered films is 1 mm. The thicknesses of the Cu layer and FeSiB film are 1 and 1.8 m, respectively. Multilayered FeSiB/Cu/FeSiB films with
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