Preparation And Their Magnetostatic And Microwave Electromagnetic Properties Of Glass-coated Alloy Microwires

The glass-coated alloy microwires (GAM) as one kind of novel one-dimensional alloy—glass composites show unique magnetic and high frequency electromagnetic properties. The outstanding characteristic of the GAM is the adjustable magneto-elastic anisotropy which determines the magnetostatic and high frequency electromagnetic properties. Therefore the magnetostatic, micowave permeability and permittivity of GAM are expected to be adjustable. The GAM have considerable potential of research and application for the high frequency electromagnetic wave filtering and absorbing. However, only sporadic study is given till now. Thus the synthesis technology, magnetostatic properties, microwave electromagnetic properties and the effect of annealing on the properties of the GAM were systematically investigated in this dissertation. Theoritically, controlment of the magnetostatic and microwave properties by the magnetic anisotropy was analysed. Furthermore, the collective length effect was put forward to control the magnetic and microwave properties. Experimentally, the geometrical dimension, length, number and annealing on the magnetostatic and microwave properties were mainly investigated.The mechanism analysis and computer simulation were carried out on the magnetostatic and microwave electromagnetic properties of the GAM. The results show that magnetic anisotropic field of GAM is significantly dependent on their internal stress and length, while the internal stress of the GAM relates to the composition and geometrical dimension. The microwave permittivity of the GAM associates with the circumferential permeability via the impedance of GAM. The microwave permeability is related to the saturation magnetization and magnetic anisotropic field. The natural ferromagnetic resonance (NFMR) frequency increases while the microwave permeability decreases with the increase of the magnetic anisotropic field.Amorphous Fe_73.5Cu_1.0Nb_1.0V_2.0Si_13.5B_9.0 and Co_69.1Fe_5.2Ni₁B_14.8Si_9.9 microwires, whose diameters are in the range of 6.3²8.3μm and 14.0³5.1μm with positive and negative magnetostriction coefficient respectively, coated by borosilicate glass were synthesized with argon shield and water-cooling by the Taylor-Ulitovsky technology. Investigation on the preparation technology indicated that the geometrical dimension of the GAW can be controlled by the wire-drawing speed and melting temperature, and the microstructure can be controlled by the cooling speed.The magnetostatic properties of the GAW were extensively examined. It is found that the axial magnetic anisotropy and coercive field increase with the enhancement of the saturation magnetostriction coefficient, the ratio of glass thickness to alloy core diameter, the length and number of the GAW which are not so short. The magnetic anisotropy increases rapidly as the number of the GAW is around 10. The collective critical lengths of an array of FeCuNbVSiB and CoFeNiSiB microwires are between 1² mm and larger than 10 mm respectively.The microwave electromagnetic properties of the GAW—dielectric composites were systematacially investigated in the frequency range of 2¹8 GHz. The microwave electromagnetic properties of the composites are adjustable and substantively determined by the magnetic anisotropy and the effective volume fraction. The electric dipole resonance (EDR) frequency is associated to a certain extent with the NFMR as the microwave permittivity depends on the microwave permeability of the GAW with an adjustable range of some GHz .The effect of annealing process on the magnetostatic and microwave electromagnetic properties of the GAW was also studied. The soft magnetic properties of GAW can be improved by annealing at 470℃and 360℃with 16¹7 nm grain and release of stress for FeCuNbVSiB and CoFeNiSiB microwires respectively. An increase in the annealing temperature can lead to an increase at first and then decrease for the real part of permeability, real part of permittivity and EDR frequency, while the microwave magnetic loss and NFMR frequency mirrors with the change of the real part of permeability. The annealing of the FeCuNbVSiB microwires at 470℃leads to the maximization of the permeability, the minimum of the magnetic loss and the mediacy of the NFMR frequency.