Comprehensive investigation of magnetoimpedance on micromachined soft magnetic material

Magnetoimpedance (MI) effects arise from changes in permeability associated with the skin effect and ferromagnetic resonance, making them highly attractive for sensitive magnetic sensors and soft magnetic material characterization. Conventional MI elements typically have lateral dimensions of 0.5–10 mm. In this study, we successfully miniaturized MI elements to sub-100-μm scales using thin-film fabrication techniques. We investigated thin-film MI elements with an approximately 1:1 width-to-thickness aspect ratio, focusing on structures with thicknesses and widths of several micrometers and lengths below 100 μm. Magnetic anisotropy control was achieved using Joule heating, since conventional static field annealing becomes ineffective at such small dimensions due to strong demagnetizing effects. The results demonstrate that Joule heating significantly improves MI characteristics, yielding clear and desirable double-peak impedance profiles. Furthermore, the MI response was found to depend strongly on the input power. A maximum impedance change ratio of 130% was achieved for an element length of 100 μm.