EQ-06 Comprehensive investigation of magnetoimpedance on micromachined soft magnetic material
Creators: Ziyue Wang
Hiroaki Kikuchi
Publisher: name: IEEE
Year: 2025

Magnetoimpedance (MI), utilizes the skin effect and ferromagnetic resonance via permeability changes [1], is used in highly sensitive sensors and for a qualification of soft magnetic materials. So far, element length is over several mm (2–10mm, typical), while we have miniaturized element to less than 1 mm using thin-film [2]. However, when length becomes below 100 μm, a demagnetizing effect reduces the sensitivity, impedance changes and makes controlling anisotropy difficult. In this study, we explored the feasibility of fabricating thin-film elements having several μm thick, wide, and less than 100 μm long, with a nearly 1:1 sectional aspect ratio, using photolithography and focused ion beam techniques, then their MI properties were examined. To control anisotropy, we adopted Joule heating [3], as static field annealing is ineffective for these sizes due to the demagnetizing effect. Applying Joule heating to such small volumes is also challenging. Fig. 1 shows the applied field dependence of impedance for micromachined elements with and without Joule heating. The element dimensions are 2μm-thick/wide, 100μm-long, made of amorphous CoZrNb. Impedance was measured at 1 GHz with -20 dBm. The as-deposited state shows a discontinuous jump, typical of properties with inclined easy axis from width direction due to shape anisotropy. After Joule heating with 20 mA, those properties changed to preferable profiles for sensing application, showing a double peak profile due to easy directions parallel to width direction. Additionally, when 0 dBm power was applied to the element, the profile was similar to that after Joule heating, indicating the potential for controlling anisotropy with relatively higher power—a new finding in this study. However, this also suggests the need to carefully manage input power for small volume elements as shown in Fig 2, the results of the elements with 1μm-thick /wide, 30μm-long. The impedance changes when the input power is -20 dBm, while showing no changes with 0 dBm due to the crystallization of the element. Throughout this study, the maximum change ratio of 78% was also obtained.References: [1] L. V. Panina, K. Mohri, Appl. Phys. Lett. 65 (1994) 1189–1191. [2] H. Kikuchi et al. , IEEE Magn. Lett., 10 (2019) 8107205. [3] H. Kikuchi et al. , IEEE Trans. Magn., 58 (2022) 2000905.
Magnetoimpedance (MI), utilizes the skin effect and ferromagnetic resonance via permeability changes [1], is used in highly sensitive sensors and for a qualification of soft magnetic materials. So far, element length is over several mm (2–10mm, typical), while we have miniaturized element to less than 1 mm using thin-film [2]. However, when length becomes below 100 μm, a demagnetizing effect reduces the sensitivity, impedance changes and makes controlling anisotropy difficult. In this study, we explored the feasibility of fabricating thin-film elements having several μm thick, wide, and less than 100 μm long, with a nearly 1:1 sectional aspect ratio, using photolithography and focused ion beam techniques, then their MI properties were examined. To control anisotropy, we adopted Joule heating [3], as static field annealing is ineffective for these sizes due to the demagnetizing effect. Applying Joule heating to such small volumes is also challenging. Fig. 1 shows the applied field dependence of impedance for micromachined elements with and without Joule heating. The element dimensions are 2μm-thick/wide, 100μm-long, made of amorphous CoZrNb. Impedance was measured at 1 GHz with -20 dBm. The as-deposited state shows a discontinuous jump, typical of properties with inclined easy axis from width direction due to shape anisotropy. After Joule heating with 20 mA, those properties changed to preferable profiles for sensing application, showing a double peak profile due to easy directions parallel to width direction. Additionally, when 0 dBm power was applied to the element, the profile was similar to that after Joule heating, indicating the potential for controlling anisotropy with relatively higher power—a new finding in this study. However, this also suggests the need to carefully manage input power for small volume elements as shown in Fig 2, the results of the elements with 1μm-thick /wide, 30μm-long. The impedance changes when the input power is -20 dBm, while showing no changes with 0 dBm due to the crystallization of the element. Throughout this study, the maximum change ratio of 78% was also obtained.References: [1] L. V. Panina, K. Mohri, Appl. Phys. Lett. 65 (1994) 1189–1191. [2] H. Kikuchi et al. , IEEE Magn. Lett., 10 (2019) 8107205. [3] H. Kikuchi et al. , IEEE Trans. Magn., 58 (2022) 2000905.