Permalloy-Based Thin Film Structures: Magnetic Properties and the Giant Magnetoimpedance Effect in the Temperature Range Important for Biomedical Applications

Permalloy-based thin film structures are excellent materials for sensor applications. Temperature dependencies of the magnetic properties and giant magneto-impedance (GMI) were studied for Fe19Ni81-based multilayered structures obtained by the ion-plasma sputtering technique. Selected temperature interval of 25 degrees C to 50 degrees C corresponds to the temperature range of functionality of many devices, including magnetic biosensors. A (Cu/FeNi)(5)/Cu/(Cu/FeNi)(5) multilayered structure with well-defined traverse magnetic anisotropy showed an increase in the GMI ratio for the total impedance and its real part with temperature increased. The maximum of the GMI of the total impedance ratio Delta Z/Z = 56% was observed at a frequency of 80 MHz, with a sensitivity of 18%/Oe, and the maximum GMI of the real part Delta R/R = 170% at a frequency of 10 MHz, with a sensitivity of 46%/Oe. As the magnetization and direct current electrical resistance vary very little with the temperature, the most probable mechanism of the unexpected increase of the GMI sensitivity is the stress relaxation mechanism associated with magnetoelastic anisotropy.This work was supported in part by the Russian Foundation for Basic Research under grants mol nr no. 16-32-50054 and by the ELKARTEK grant KK-2016/00030 of the Basque Country Government

Magnetic properties and giant magnetoimpedance of surface modified Co-based amorphous ribbons with carbon covering

Fe3Co66Cr3Si16B12 and Fe6Co60Ni10Si14B10 amorphous ribbons were surface modified in toluene at room temperature. Such a treatment resulted in deposition of thin carbon-based layer. As a result of the carbon covering deposition the stress distribution in the near-surface layers was changed due to partial compensation of the initial quenching stresses. Comparative analysis of magnetic and magnetoimpedance properties of as-quenched and surface modified ribbons confirms changes in effective magnetic anisotropy as a result of surface treatment. An increase of the corrosion resistance of the ribbons with carbon covering can be useful for the development amorphous ribbon based magnetic biosensor

Magnetoimpedance Effect in the Ribbon-Based Patterned Soft Ferromagnetic Meander-Shaped Elements for Sensor Application

Amorphous and nanocrystalline soft magnetic materials have attracted much attention in the area of sensor applications. In this work, the magnetoimpedance (MI) effect of patterned soft ferromagnetic meander-shaped sensor elements has been investigated. They were fabricated starting from the cobalt-based amorphous ribbon using the lithography technique and chemical etching. Three-turn (S1: spacing s = 50 μm, width w = 300 μm, length l = 5 mm; S2: spacing s = 50 μm, width w = 400 μm, length l = 5 mm) and six-turn (S3: s = 40 μm, w = 250 μm, length l = 5 mm; S4: s = 40 μm, w = 250 μm and l = 8 mm) meanders were designed. The ‘n’ shaped meander part was denominated as “one turn”. The S4 meander possesses a maximum MI ratio calculated for the total impedance ΔZ/Z ≈ 250% with a sensitivity of about 36%/Oe (for the frequency of about 45 MHz), and an MI ratio calculated for the real part of the total impedance ΔR/R ≈ 250% with the sensitivity of about 32%/Oe (for the frequency of 50 MHz). Chemical etching and the length of the samples had a strong impact on the surface magnetic properties and the magnetoimpedance. A comparative analysis of the surface magnetic properties obtained by the magneto-optical Kerr technique and MI data shows that the designed ferromagnetic meander-shaped sensor elements can be recommended for high frequency sensor applications focused on the large drop analysis. Here we understand a single large drop as the water-based sample to analyze, placed onto the surface of the MI sensor element either by microsyringe (volue range 0.5−500 μL) or automatic dispenser (volume range 0.1−50 mL)