Research Of The Soft Magnetic Properties And GMI Effect In Amorphous And Nanocrystalline Glass-covered Microwires

Recently, a large increase of interest has been concentrated on giant magneto-impedance and its applications, for its promising technological applications such as magnetic record and magnetic sensors. A summary of research on GMI effect is presented in this thesis. Amorphous Fe-based, Fe/Co-based, Co-based microwires are prepared by the Taylor-Ulitovsky method. Different annealing methods are used to improve their magnetic properties. We studied the soft magnetic properties and GMI effect on annealing conditions and geometry dimension.The main results are listed as below:1. Preparation and research of Fe-based glass-covered microwires.Nanocrystalline Fe_73.5Cu₁Nb₃Si_13.5B₉ samples with different diameters are obtained by annealing the amorphous wires at 570℃. The relationship between GMI effect and the metallic core diameter has been investigated by four-points method. The results show that the GMI ratios first increase then decrease with the increase of metallic core diameter. The highest MI ratio of 251% is obtained in the nanocrystalline microwires with 30μm in diameter.2. Preparation and research of FeCo-based glass-covered microwires. The changes in the structure and magnetic properties of Fe₄₆Co₁₉Si_8.5B₁₅Ni_11.5 glass-covered microwires have been investigated by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), ⁵⁷Co Mossbauer spectroscopy (MS) and magnetization measurements. Results show that thermal treatment will reduce disorder range in the specimens via structural relaxation and crystallization process. The metastable phases α-Fe/Co will appear after annealing. The microwires annealed at 520℃ exhibit the best soft magnetic properties and GMI effects.3. Preparation and research of Co-based microwires. Isothermal and DC joule-heating with stress are performed on Co_69.20Fe_4.16Si_12.35B_10.77Cr_3.42Mo_0.1 glass-covered microwires. Results show that(1) Furnace thermal annealing will deteriorate the magnetic properties.(2) The optimal density current of joule annealing is j=30 A/mm².(3) Microwires are annealed under tensile stresses at same joule current density.