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.     

非晶玻璃包裹细丝的制备与铁磁共振性能的应用

非晶玻璃包裹细丝不仅具有电、磁、强度和塑性等方面的显著特点,而且具有突出的自然铁磁共振性能,作为吸波材料具有潜在的应用价值.阐述了玻璃包裹熔融纺丝法制备非晶玻璃包裹细丝的基本原理和实验参数,介绍了细丝产生铁磁共振性能的基本原理,及在吸波材料方面的应用.     

The effect of mechanical stress on Ni63.8Mn11.1Ga25.1 microwire crystalline structure and properties

We studied structure and magnetic properties of Heusler alloy microwires. The dependence of the phase composition of the annealed microwires on the presence of glass coating has been found. The crystalline structure of the glass-coated samples is composed of two cubic crystalline phases of different density. The samples annealed without coating are in the single-phase state. The two-phase state is supposed to be caused by intrinsic stresses resulted from the action of opposite sign stresses in different microwire sections. The magnetic properties of the fabricated Heusler-type microwires differ from their bulk and thin film counterparts. Annealing of microwires considerably affect magnetic properties at room temperature. Unusual magnetic behavior is connected with two-phase structure of microwires.     

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。     

Magnetic properties of micro- and nanowires in the superhigh-frequency range

The skin-effect theory is presented using the example of an amorphous ferromagnetic material taking into account the ferromagnetic resonance. The theoretical dependence of the impedance of a microwire on its magnetic permeability is determined. The results allow analyzing experiments on studying the high-frequency properties of amorphous microwires.     

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.     

Design of multilayer microwires with controllable magnetic properties: Magnetostatic and magnetoelastic coupling

Novel two-magnetic-phase multilayer microwires with outstanding controllable behaviour are introduced. They are obtained by suitable combined processing techniques, such as the quenching and drawing method, sputtering and/or electroplating, and consist of a magnetic nucleus, intermediate non-magnetic layers and an outer magnetic layer. In this work, an ultrasoft CoFe-based amorphous nucleus and a magnetically harder crystalline CoNi outer layer are considered. The magnetostatic interaction between magnetic phases is proven to give rise to antiferromagnetic-like coupling, resulting in biasing of the magnetic behaviour of the soft nucleus. In addition, the effective magnetic anisotropy of the latter is tailored by the magnetoelastic coupling between the nucleus and the external layers through the stresses induced during the fabrication process and by their differential thermal expansion coefficients. This new family of microwires shows excellent magnetic properties which, being tailorable, make them ideal materials for novel or optimized elements in sensor devices.     

Effect of composite origin on magnetic properties of glass-coated microwires

We observed that magnetic properties (Giant magneto.-impedance effect and domain wall dynamic) of glass-coated microwires are closely related with the peculiarities of the fabrication technique involving rapid solidification of metallic alloy surrounded by glass coating from the melt.We present studies of the interfacial layer between the metallic nucleus and glass coating and studies of the inhomogeneities related with fabrication process of thin ferromagnetic microwires.We observed gas bubbles within the glass coating with volume content of about 8–12%. The sizes of the bubbles were between 1 and 15 μm. The existence of such bubbles might be the origin of the inhomogeneities in the internal stresses distribution.Using scanning electron microscope JEOL JSM-6610 we obtained the image of the interfacial layer and the elements distribution within the glass coating and metallic nucleus. This allowed us to estimate the thickness of the interfacial layer.Understanding of the origins of the interfacial layer and defects may help for improvement of the existing technology for thin composite wires fabrication and enhance their magnetic properties.     

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.     

电塑性冷拔对水淬非晶丝GMI性能的影响

电塑性冷拔是基于金属材料电塑性效应的一种加工工艺,在非晶丝材料后处理中引入电塑性冷拔工艺,对非晶丝材料的塑性变形、组织结构有显著影响。适当的脉冲电流不仅能显著改善非晶丝的加工性能及力学性能,还能减少非晶丝表面的缩孔、缩松,提高非晶丝材料的表面光洁度,改善非晶丝材料的巨磁阻抗(GMI)性能。     

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.     

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.     

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.     

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.     

Electroplated Bimagnetic Microwires: From Processing to Magnetic Properties and Sensor Devices

Multilayer microwires with biphase magnetic behavior are revisited in this work. They are fabricated by the combination of ultrarapid solidification and electroplating techniques, and they are composed by ferromagnetic nucleus, intermediate glass layer, and ferromagnetic outer shell. Different magnetic configurations have been explored: soft/hard (CoFeSiB/CoNi and FeSiB/CoNi), soft/soft (CoFeSiB/FeNi), and hard/soft (FePtSi/FeNi). Their magnetic properties are mainly determined by the magnetic interactions between both magnetic phases: (I) a magnetoelastic coupling that arises from the mechanical stresses induced during the growth of the external magnetic shell and (II) a magnetostatic bias field that arises from uncompensated magnetic charges of the hard layer. Most outstanding static (i.e., low-field hysteresis loops) and dynamic (i.e., magnetoimpedance and ferromagnetic resonance) properties are reviewed in this article. The possibility to tailor the magnetization reversal of the soft phase through the tuning of those magnetic couplings places multilayer biphase microwires in a very competitive position as functional sensing elements suitable for a number of technological applications. In particular, we focus on their use in multifunctional sensor devices and fluxgate applications.     

A three-layer model of an amorphous microwire

A theory of a three-layer model for an amorphous microwire is studied. The obtained theoretical results are confirmed by an experiment. For a more precise comparison of the theory with the experiment, a series of experimental measurements is needed, which are also discussed in the paper.     

熔淬态非晶带中晶化相数量密度的确定

本文利用透射电子显微镜对进口和国产非晶带材的非晶化程度进行了精确测定.结果表明,XRD实验只能粗略的判定材料是否为非晶态；进口带材在熔淬态下为完全的非晶态,而国产带材并非完全的非晶态,其磁性相α-Fe(Si)的尺寸为100nm左右,数量密度大约为1015 m-3数量级.     

磁致Fe78Si9B13非晶合金纳米晶化磁矩的理论计算

用低频脉冲磁场处理非晶Fe78Si9B13合金,在低温下发生了纳米晶化,利用M?ssbauer谱和LDJ9600震动样品磁强计进行了微结构和磁性分析.借助于固体与分子经验电子理论中的BLD方法,计算了非晶Fe78Si9B13合金磁致低温纳米晶化前后的价电子结构,并算出了磁矩,其理论计算值与实验测定值的误差小于7%,满足一级近似要求,说明从价电子层次上计算非晶合金的磁矩是可以实现的.     

Calculation of cooling rate of amorphous aluminum alloy melt-spun ribbons

Based on the heat transfer theory and liquid solidification theory, the heat transfer during the rapid solidification process of amorphous ribbons prepared by melt spinning was approximately modeled by one-dimensional heat conduction equation. Besides, integration with the temperature gradient, the relationship between the ribbon thickness and solidification time was derived according to the boundary conditions of ribbon-copper wheel. A simply theoretical model was obtained to calculate the cooling rates of aluminum amorphous ribbons. According to the above theoretical model, the critical cooling rate of aluminum amorphous ribbons by melt spinning is above 10^6 K/s, which proves that the aluminum based alloys belong to the marginal glass forming ability of alloys. The calculated results are in good agreement with other estimated values reported previously.