Giant magnetoimpedance for biosensing: Advantages and shortcomings

Biosensors are an important area of modern sensor applications. Magnetoimpedance (MI) phenomenon was proposed for biosensing in 2003. Since that MI biosensor prototypes based on amorphous ribbons, multilayered structures, amorphous rapidly quenched wires and glass covered microwires were designed and tested. In this paper the advantages and shortcomings of MI-based devices for magnetic labels or label-free biodetection are discussed in view of recent results.     

Recent advances in studies of magnetically soft amorphous microwires

In this paper, we present the giant magneto-impedance (GMI) effect (real part of longitudinal impedance, Z, and of the off-diagonal impedance) and hysteretic magnetic properties of amorphous glass-coated microwires with different compositions possessing nearly zero, positive and negative magnetostriction constant and metallic nucleus diameter ranging between 6 and 16 μm. Enhanced soft magnetic properties (low coercivity of about 4 A/m) and high-GMI effect have been observed in Co-rich microwires with vanishing magnetostriction constant. The magnetic anisotropy field of these microwires depends on the ratio between metallic diameter, d and total microwires diameter, D. Stress-sensitive magnetic properties have been obtained in Fe-rich microwires after stress annealing: hysteresis loop stress-annealed (SA) microwires drastically changes under applied stress. A variety of hysteresis loops with different hysteresis loops can be obtained in Fe-rich microwires changing the conditions (time and/or temperature) of the stress annealing. The obtained results allow us to tailor the microwire magnetic properties for magnetic sensors applications through selection of their composition and/or geometry and by thermal treatment.     

Influence of demagnetization effect on giant magneto-impedance of soft ferromagnetic metal

The magneto-impedance (MI) of an amorphous ferromagnetic ribbon with nominal composition Fe₄₀Ni₄₀B₂₀ and of different lengths is measured using non-contact method at 1 MHz frequency. In the presence of static magnetic field around 30 Oe, the MI of the ribbon of long length is reduced by nearly 90%. With decreasing sample dimension the extent of reduction in MI becomes smaller. The MI of a ferromagnetic metallic system results from the e.m field’s screening which in turn depends on the magnetic response of the sample. The demagnetization field of smaller sample size reduces the magnetic response which in turn decreases the field sensitivity of MI. The phenomenology based on the Landau–Gilbert equation predicts similar qualitative behaviour of MI.     

Giant magnetoimpedance in thin amorphous and nanocrystalline microwires

We present the results on Giant magneto-impedance effect (GMI) in amorphous and nanocrystalline microwires at frequencies until 4 GHz, paying special attention to tailoring the frequency and magnetic field dependence of the GMI effect. Correlation between magnetoelastic anisotropy and magnetic field dependences of diagonal and off-diagonal impedance components are observed.     

Tunable properties of microwire composites at microwave frequency

Tunable electromagnetic properties (permeability and permittivity) of composites filled with glass-coated microwires under external magnetic field were investigated experimentally. The microwire composites have been measured with 7 mm coaxial airline fixture and vector network analyzer from 0.01 to 18 GHz. The ferromagnetic resonance may contribute to the tunability of permeability of microwire composites. The tunability of effective dielectric permittivity may be attributed to the magneto-impedance effect. The microwire composites are promising candidates for smart or tunable applications at microwave frequency.     

Magnetic Anisotropy and Super-Sensitive Stress-Magnetoimpedance in Microwires with Positive Magnetostriction

Physics of the Solid State - In glass-coated Co71Fe5B11Si10Cr3 amorphous ferromagnetic microwires subjected to current annealing, a record sensitivity of the magnetoimpedance (MI) to mechanical...     

High-frequency magneto-impedance in metastable metallic materials: An overview

The giant magneto-impedance effect (GMI) is a common feature of a wide class of metastable ferromagnetic alloys. This effect can be enhanced by submitting the as-prepared materials to suitable thermal treatments. Recently, a remarkably high magneto-impedance response has been observed in the GHz region for several systems. The increase in miniaturization of telecommunication devices dramatically increases the working frequencies; as a consequence, the interest in studying magneto-impedance effect leads to microwave region.     

Study of domain structure and magnetization reversal after thermal treatments in Fe40Co38Mo4B18 microwires

We have studied the effect of thermal treatment on the magnetic domain structure and magnetic reversal process of amorphous and nanocrystalline Fe₄₀Co₃₈Mo₄B₁₈ microwires. The domain structure and the magnetization reversal of amorphous FeCoMoB microwires reflect the complex stress distribution introduced by the glass coating. Hence, the thickness of radial domain structure decreases with temperature and the temperature dependence of the switching field presents a discontinuous behavior. After nanocrystallization, the domain structure of FeCoMoB microwire is almost constant within the temperature range 10-400 K and the switching field decreases almost linearly with temperature mostly because of the decrease of saturation magnetization.     

Tunable effective permittivity of composites based on ferromagnetic microwires with high magneto-impedance effect

The effect of the external magnetic field on the dispersion of the effective permittivity in a single array of parallel CoFe-based amorphous wires is demonstrated by measuring the transmission/reflection spectra in free space in the frequency band of 0.9–17 GHz. The magnetic field is applied along the wires, sensitively changing their magnetisation and high-frequency impedance. Based on the measurements of magneto-impedance in a single wire and S-parameters of composites in free space, we show the correlation between the magneto-impedance and the field dependence of the effective permittivity.     

The effects of temperature and frequency on the magnetization switching mode in circular MI sensors

This paper presents results computed using a meshless method in a point collocation formulation to investigate the effects of temperature and frequency on the magnetization switching mode in the circular amorphous magneto-impedance sensor (element). Specifically, the solutions characterizing the MI effect are solved from a set of coupled nonlinear equations consisting of the Maxwell’s equations, the Landau-Lifshitz-Gilbert equation, and the thermal diffusion equation. This coupled nonlinear space-time model predicts the formation and propagation of dynamic domain walls in switching and it is shown how they contribute to experimentally observed temperature and frequency effects. Computed results (that agree well with reported experimental data) suggest radial domain walls may play a larger role in the MI effect than originally believed even for the realistic conditions considered here at 1 MHz or more.     

Integral imager: Prototype scientific performances

Summary The Imager proposed for the gamma-ray satellite project INTEGRAL is based on a multilayer two-dimensional array of CsI(TI) elements viewed by Si photodiodes. The total active area is ≈2500 cm². The operative energy interval ranges from 0.05 to 10 MeV. A prototype version of this instrument, ready to be tested on a ballon-borne experiment, has been realized. In this article the expected performances of the instrument are presented, toghether with the first calibration results of the prototype. Paper presented at the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992.     

Influence of Nb substitution for Fe on the magnetic and magneto-impedance properties of amorphous and annealed Fe76.5−xSi13.5B9Cu1Nbx (x=0–7) ribbons

We report a systematic study of the influence of Nb substitution for Fe on the magnetic properties and magneto-impedance (MI) effect in amorphous and annealed Fe_76.5−xSi_13.5B₉Cu₁Nb_x (x=0, 1, 2, 3, 4, 5, 6, and 7) ribbons. The amorphous ribbons were annealed at different temperatures ranging from 530 to 560 °C in vacuum for different annealing times between 5 and 20 min. We have found that for the as-quenched amorphous ribbons, the substitution of Nb for Fe first increases the saturation magnetization (M_s) and decreases the coercivity (H_c) until x=3, for which the largest M_s∼152 emu/g and the smallest H_c∼1.3 Oe are obtained, then an opposite trend is found for x>3. The largest MI ratio (ΔZ/Z∼38% at f=6 MHz) is achieved in the amorphous ribbon with x=3. A similar trend has been observed for the annealed ribbons. The most desirable magnetic properties (M_s∼156 emu/g and H_c∼1.8 Oe) and the largest MI ratio (ΔZ/Z∼221% at f=6 MHz) are achieved for the x=3 sample annealed at 540 °C for 15 min. A correlation between the microstructure, magnetic properties, and MI effect in the annealed ribbons has been established.     

Co基金属纤维不对称巨磁阻抗效应

以直径32 μm的熔体抽拉Co基非晶金属纤维为研究对象, 分析了该纤维不同激励条件下的巨磁阻抗(giant magneto impedance, GMI)效应. 实验结果表明: 这类纤维的GMI效应具有不对称性特点, 即 AGMI (asymmetric GMI)效应. 同时, 发现AGMI效应随激励条件不同而变化, 随交流频率或者激励幅值升高而逐渐增强; 当存在一定偏置电压时, AGMI效应大幅增强. 通过研究纤维的磁化过程, 分析了Co基金属纤维的AGMI效应. 由于Co基熔体抽拉纤维具有螺旋各向异性以及磁滞的存在使得GMI效应具有不对称性, 频率升高或者激励电流幅值增加有利于壳层畴环向磁化, AGMI增强. 当在纤维两端施加偏置电压时, 偏置电流诱发环向磁场增强了环向磁化, AGMI效应提高; 偏置电压较低时磁场响应灵敏度提高, 同时磁化翻转向高场移动, 阻抗线性变化对应的直流磁场区间增大. 这一方面拓宽了GMI传感器工作区间及灵敏度, 另一方面不利于获得更大的磁场响应灵敏度. 10 MHz (5 mA)激励时, 施加1 V强度的偏置电压后, 对应的磁场灵敏度从616 V/T 提高至5687 V/T; 偏置电压为2 V时, 灵敏度降低到4525 V/T. 因此, 可以通过适当提高环向磁场的方法获得大的磁场响应灵敏度及阻抗变化线性区域.     

Francisella tularensis detection using magnetic labels and a magnetic biosensor based on frequency mixing

A biosensor that uses resonant coils with a special frequency-mixing technique and magnetic beads as detectable labels has been established for the detection of Francisella tularensis, the causative agent for tularemia. The detection principle is based on a sandwich immunoassay using an anti-Ft antibody for immunofiltration immobilized to ABICAP^® polyethylene filters, and biotinylated with streptavidin-coated magnetic beads as labels. The linear detection range of this biosensor was found to be 10⁴–10⁶ cfu F. tularensis lipopolysaccharide (LPS) per ml. Tested sample matrices were physiological PBS buffer and rabbit serum.     

Measurement of photoelectron yield of the CDEX-10 liquid argon detector prototype

The China Dark Matter Experiment (CDEX) is a low background experiment at China Jinping Underground Laboratory (CJPL) designed to directly detect dark matter with a high-purity germanium (HPGe) detector. In the second phase, CDEX-10, which has a 10 kg germanium array detector system, a liquid argon (LAr) anti-Compton active shielding and cooling system is proposed. To study the properties of the LAr detector, a prototype with an active volume of 7 liters of liquid argon was built and operated. The photoelectron yields, as a critically important parameter for the prototype detector, have been measured to be 0.051-0.079 p.e./keV for 662 keV γ rays at different positions. The good agreement between the experimental and simulation results has provided a reasonable understanding and determination of the important parameters such as the surviving fraction of the Ar₂^* excimers, the absorption length for 128 nm photons in liquid argon, the reflectivity of Teflon and so on.     

Structural and Giant Magneto-impedance properties of Cr-incorporated Co-Fe-Si-B amorphous microwires

The investigation is focused on the effect of Cr incorporation for Co/Fe in (Co_0.5Fe_0.5)_78−xCr_xSi₈B₁₄ (x=0-12) amorphous microwires of 110 μm diameter prepared by in-water quenching technique. The rise in crystallization onset T_X1 with Cr addition revealed the elemental contribution against devitrification and a consequent thermal stability. Cr is unfavorable towards ferromagnetic ordering leading to a linear drop in Curie temperature T_ca with its rise in concentration. The presence of low Cr content upto Cr-4 at.% has been effective in drastically improving the Giant magneto-impedance (GMI) property. Cr content in the range of 4≤X≤10 has low magnetostriction and maximum field sensitivity in the as-quenched state. The GMI properties are further improved after annealing treatment. High content of Cr>10 is found to be deleterious towards GMI behavior and its consequent application as sensor material.     

Poly(glycidylmethacrylate-co-vinyl ferrocene)-grafted iron oxide nanoparticles as an electron transfer mediator for amperometric phenol detection

An amperometric phenol biosensor was constructed by using poly(glycidylmethacrylate-co-vinyl ferrocene) grafted iron oxide nanoparticles for detection of different phenolic compounds (catechol, aminophenol, phenol, p-cresol, pyrogallol). The poly(glycidylmethacrylate-co-vinyl ferrocene) and nanoparticles were characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The copolymer grafted iron oxide nanoparticles and Horseradish peroxidase (HRP) were covalently attached on gold (Au) electrode surface. The effect of pH, temperature and characteristic features such as; reusability and storage stability were studied. The electrode showed good response time within ～3 s. The electrocatalytic response showed a linear dependence on the phenolic compounds concentration ranging from 0.5 to 17.0 mM.     

Novel trends in the study of magnetically soft Co-based amorphous glass-coated wires

An overview of the recent progress and state-of-the-art results in the investigation of the amorphous glass-coated wires with nearly zero magnetostriction is presented. These versatile microwires display enhanced soft magnetic properties, which make them suitable as sensing elements in various sensors for biomedical and automotive applications. Current results on their magnetic characteristics refer to a major refinement of their core-shell magnetic structure by taking into account the interdomain wall and to the thorough analysis of the magnetization within the outer shell. Experimental techniques such as giant magneto-impedance, magneto-resistance, and magneto-optical Kerr effect measurements are employed to prove the outcome of the theoretical calculations. The impact of the magnetic structure of the outer shell on the propagation of domain walls in bistable amorphous wires is analyzed. Very recent results on the magnetization process in nearly zero magnetostrictive amorphous glass-coated wires with submicron dimensions are also reviewed.