Magnetic and microwave properties of glass-coated amorphous ferromagnetic microwires

Glass-coated amorphous FeCuNbSiB microwires were prepared by Taylor-Ulitovsky technique. X-ray diffractometry and scanning electron microscopy were used to investigate the microstructure and morphology of the glass-coated microwires respectively. The vibrating sample magnetometer and vector network analyzer were used to study the magnetostatic and microwave properties of glass-coated microwires. The experimental results show that the effective anisotropy of an array of 150 microwires of 10 mm in length is large than that of one microwire of 10 mm in diameter and an array of 150 microwires of 1 mm in diameter. The natural ferromagnetic resonance takes place as the microwave magnetic component is perpendicular to the microwires axis, and the electric dipole resonance takes place as the microwire is long or the short microwire concentration is moderate. The natural ferromagnetic resonance shifts to higher frequency with the larger microwire concentration. The electric dipole resonance is governed by the microwires length and concentration. The glass-coated FeCuNbSiB microwires can be used to design EMI filters and microwave absorbing materials.     

Giant magneto-impedance effect of two paralleled amorphous microwires

Giant magneto-impedance（GMI）is effectively enhanced by the mutual magnetic interaction between two amorphous microwires.A comparative study on GMI properties of a single wire and two wires arranged in parallel mode was reported in this work.Two-peak（TP）of impedance characteristic is presented when the dc external field changed from 0 to 320 A m^-1in two-wire system,which is attributed to successive magnetization process in two wires induced by their magnetic interaction.And the evolution of single peak to TP phenomenon,when the distance between two wires is upto 8 mm,evidences a distance dependence of transformation from successive magnetization to simultaneous via a corresponding distance dependence of magnetostatic interactions.It is proposed that the recombination of magnetic interaction and the shielding effect results in a distance dependency of GMI response.When the distance is 8 mm,the magnetization process is close to synchronous between two wires,which give rises to higher circular permeability and better GMI response.The impedance ratio DZ/Z increases from74.5 % of single wire to 172.4 % at 10 MHz.However,when the distance is upto 12 mm,the magnetic interaction is weak and magnetization process is completely independent,and GMI response decreases,relatively.This indicates that the GMI response could be effectively improved in a two-wire connection with an opticaldistance,which is promising and useful for the application of high-performance GMI sensors.     

Dimensional absorption high-frequency properties of the cast glass coated microwires

Correlation between frequency of natural ferromagnetic resonance of the cast glass coated amorphous microwires and high-frequency absorption of a composite material from this microwire is investigated. The article is published in the original.     

Magnetic properties of microwires and filiform nanostructures with elongated magnetic inclusions

We developed technological procedures for preparation of filiform nanostructures (FNSs) on the basis of stretching microwires with magnetic material cores. It is shown that disruptions of the microwire core occur for these materials during technological process of stretching due to relatively high melting temperature of magnetic alloys. As a result, FNSs with elongated magnetic inclusions are produced. An installation for the production of FNSs as well as an experimental complex for measuring magnetic properties of the produced magnetic FNSs is described in this paper. The morphology of the produced FNSs from microwires with magnetic bistability is investigated by means of scanning electron microscopy, while magnetic properties, such as magnetic response with remagnetizing pulses, hysteresis loop, and coercive force, are investigated on the developed experimental complex. The magnetic interaction during remagnetizing processes of several microwires with different coercive forces assembled in a bunch, as well as the reaction of a bunch assembled from a big number of bistable mirowires of two types with different coercive forces (soft magnetic and hard magnetic cores) upon increasing external magnetic field are also investigated. Some potential applications of the produced magnetic structures are suggested.     

Effect of a glass shell on the crystallization of Fe- and Co-based amorphous microwires

Crystallization of amorphous Fe_73.9B_13.2Si_10.9C₂ and Co_73.6B_11.2Si₁₃C₂ microwires in a glass isolation (shell) upon heating has been studied by X-ray diffraction. Crystallization of the core of an amorphous microwire starts at temperatures above 400°C. No noticeable effect of the glass shell on the crystallization of the Fe-based microwire was observed. The crystallization of the Co-based microwires with a glass shell begins at a lower temperature than the crystallization of those without a shell. There has been observed a difference in the effect of the glass shell on the crystallization of microwires of different chemical compositions.     

Relating residual stress and microstructure to mechanical and giant magneto-impedance properties in cold-drawn Co-based amorphous microwires

The effect of cold-drawing on the tensile property and giant magneto-impedance (GMI) effect of melt-extracted Co-based amorphous microwires was evaluated through detailed analyses of the distribution of residual stress and microstructural evolution. The tensile ductility and tensile strength increased gradually with cross-sectional area reduction ratio (R) until 51%, and decreased with further deformation. The microwire with R = 51% exhibits the highest tensile ductility of 1.09% and tensile strength of 4320 MPa. Structural and thermodynamic analyses reveal that it is the mechanical deformation rather than thermal activation that induces the precipitation of nanocrystals and arrests the quick extension of shear bands leading to the enhanced ductility. Interestingly, the GMI effect also attains the maximum value of 160% at 10 MHz when R = 51% (30% larger than that of the as-cast wires), before decreasing with further cold-drawing. Such an identical evolution trend of both tensile and GMI properties can be ascribed to two underlying mechanisms: the generation of longitudinal and circumferential residual stresses and the growth of deformation-induced nanocrystals during cold-drawing. The role of residual stress is established herein not only as a trigger to accelerate the amorphous-to-nanocrystalline phase transformation but also as a decisive contributor to the mechanical and GMI performance. The unique simultaneous improvement of both mechanical and GMI properties of cold-drawn Co-based microwires opens up new possibilities for a variety of engineering applications, such as high-performance magnetic, stress and biological sensors.     

Experimental measurement of residual stresses in microwires

Methods of measurement of residual stresses in cast amorphous microwires are submitted. The obtained experimental results confirm the earlier given theoretical conclusions.     

Magnetic properties of Fe75Si10B15 amorphous metallic wires

Effects of the temperature of a preliminary treatment, specimen length, and elastic tensile stresses on magnetic properties of amorphous metallic wires of composition Fe₇₅Si₁₀B₁₅ have been investigated. It has been revealed that the temperature of the pretreatment and the length of the wires have important influence on their magnetic properties. As the wire length decreases, a segment appears in the functional dependence of the differential magnetic permeability of the wire on the external magnetic field where the permeability remains constant, which indicates a change in the fundamental mechanism of magnetization of the wire. It has been shown that the behavior of the experimental functional dependence of the coercive force and differential permeability on applied tensile stresses may be explained in the context of the model of propagation of domain walls that separate oppositely magnetized domains in the core of the wire with allowance for the dissipative term.     

超长五重对称铜微米线的水热合成

利用简单水热法制备了高质量的超长铜微米线,并采用X射线衍射(XRD)仪、扫描电镜(SEM)氮气吸附表征了产品的结构和形貌、织构性质。结果表明,所得铜微米线具有五重对称的正五棱柱状孪晶结构。铜微米线的形成,被归因于CTAB对铜{100}面的吸附和铜晶体结构内部张力的协同作用。并且研究了产品对过氧化氢辅助的罗丹明B的催化脱色性能。在微米铜上过氧化氢辅助的罗丹明B脱色反应的表观反应速率常数(ka=0.004 84 min~(-1))为体相铜的(k_a=0.0014 min~(-1))3.5倍,这归因于前者较高比表面积和微米尺寸。本制备方法具有产率高(高达85.9%)、操作简单等优点,易于放大制备。     

玻璃包覆纯铜微丝耐腐蚀性能及电学性能

制备硼硅酸盐玻璃包覆纯铜微丝,其主要尺寸范围为：铜丝直径4-30μm,玻璃包覆层厚度2-8μm;对微丝的耐腐蚀性能和电学性能进行评价。结果表明：玻璃包覆纯铜微丝在中性盐雾实验条件下,抗潮热盐雾腐蚀时间在240 h以上;对于外径25μm、包覆层厚度3.2μm和外径18μm、包覆层厚度2.5μm玻璃包覆纯铜微丝,平均击穿电压分别达到1 174 V和774 V,耐击穿电压分别在1 050 V和660 V以上;外径25μm、包覆层厚度3.2μm的玻璃包覆纯铜微丝抗软化击穿温度大于400℃。     

Effect of nanocrystallization on giant magnetoimpedance effect of Fe-based microwires

We studied giant magnetoimpedance (GMI) effect and magnetic properties of Fe_70.8Cu₁Nb_3.1Si_14.5B_10.6 and Fe_71.8Cu₁Nb_3.1Si₁₅B_9.1 Finemet microwires. We observed that GMI effect and magnetic softness of glass-coated microwires produced by the Taylor–Ulitovski technique can be tailored either controlling magnetoelastic anisotropy of as-cast FeCuNbSiB microwires, and/or controlling their structure by heat treatment or by changing the fabrication conditions. High GMI effect has been observed in as-prepared Fe-rich and heat treated microwires with nanocrystalline structure.     

泰勒法制备的Ni-Mn-In-Co合金纤维的磁热效应

采用泰勒法制备了直径范围在30~100μm之间的玻璃包裹Ni-Mn-In-Co合金纤维。利用综合物性测量系统（PPMS）研究了磁场对制备态和退火态纤维马氏体相变温度的影响,并且从M-B曲线中分别计算得出了制备态和退火态纤维的磁热效应。研究结果表明：制备态纤维在室温下为7M马氏体结构。在制备态和退火态纤维中,奥氏体相变开始温度随外加磁场变化速率（ΔAs/ΔB）分别为-1.6和-4 K/T。退火态纤维在As点附近发生磁场诱发马氏体向奥氏体逆相变。退火态纤维最大磁熵变为3.0 J/（kg·K）,远大于制备态纤维的0.5 J/（kg·K）。Ni-Mn-In-Co合金纤维的大磁熵变和低成本使其成为最具潜力的磁制冷材料之一。     

Stress tunable microwave absorption of ferromagnetic microwires for sensing applications

In the present work, we have studied the low field absorption (LFA) at 9 GHz of a set of Co-based glass-coated microwires in the presence of tensile stresses along the wire axis. The results reveal that the absorption profiles bear valve-like features associated with microwave magnetoimpedance effect. The stress applied along the wire axis compensates the reverse effect of magnetic field on absorption. The peak shown in the derivative LFA spectra becomes wider with increasing stress and moves to higher field, corresponding to the magnetization process. A larger ratio of metal to total diameter was found to be favorable to microwave absorption due to the smaller anisotropy and also gave rise to a larger magnetostriction constant. The influences of stress/magnetic field on the absorption as well as the shift of feature stress with wire geometry were discussed in the context of an effective microwire-based sensor design. Calculations of magnetostriction constant by the derived field dependence of anisotropy field were also performed to demonstrate the usefulness of stress tunable microwave absorption characteristics as a research tool.     

Superelasticity and fatigue in oligocrystalline shape memory alloy microwires

In oligocrystalline shape memory alloys, the total grain boundary area is smaller than the surface area of the specimen, leading to significant effects of free surfaces on the martensitic transformation and related shape memory and superelastic properties. Here we study sample size effects upon the superelastic characteristics of oligocrystalline microwires after one loading cycle and after many. Cu-Zn-Al wires with diameters ranging from ∼100 down to ∼20 μm are fabricated by the Taylor liquid processing technique and characterized through both uniaxial cyclic tensile testing and mechanically constrained thermal cycling. The energy dissipated per superelastic cycle increases with decreasing wire diameter, and this size effect is preserved after extensive cycling despite a significant transient evolution of the superelastic response for early cycles. We also present fatigue and fracture data, indicating that oligocrystalline wires of this normally brittle alloy can exhibit fatigue lifetimes two orders of magnitude improved over conventional polycrystalline Cu-Zn-Al.     

金刚石微丝拉拔模具微细超声加工技术

金属微丝在是指直径在0.10 mm以下的各种金属丝。金属微丝不但具有金属材料本身固有的一切优点,还具有非金属材料的一些特殊性能,例如高强度,高弹性,良好的导电性、导热性、耐磨防腐性、耐高温、热稳定性,较好的屏蔽、防磁、防辐射性能,不易产生静电效应等,被广泛应用于国民经济各个领域。现代科技的发展需求促使金属微丝向精、微的方向拓展,对金刚石微丝拉拔模具的精度提出了更高的要求,而我国对于该类模具的加工精度与日本、德国相差较远。作者在前期研究的基础上对金属微丝拉拔模具关键技术——微细超声加工技术进行了深入的研究,加工的模具尺寸误差为0.42μm,圆度误差为0.18μm,完全达到了日本和德国的标准,达到国际领先水平。