巨磁阻抗传感器敏感材料的选择

利用巨磁阻抗(GMI)效应来研制传感器,敏感材料的选择非常关键,其GMI性能的好坏直接决定了GMI磁传感器的灵敏度水平.讨论了GMI材料的选择标准,列出了能够产生GMI效应的各种材料,并分析和评述了这些GMI材料的软磁特性、GMI效应及其在传感器上的可能应用,提供了设计高性能GMI传感器的候选材料,这些材料以及新型材料的开发为GMl传感器的研制创造了有利的条件,将会促进GMI传感器的发展与应用.     

Sensors development using its unusual properties of Fe/Co-based amorphous soft magnetic wire

In this paper, the unusual properties of amorphous soft magnetic wire with Fe-based or Co-based in compositions have been discussed: giant magnetoimpedance effect (GMI), giant stress-induced impedance effect, large Barkhausen effect, magnetostriction effect. Sensor operating principles and applications exploiting these unusual properties have also been discussed: magnetic field sensors, position sensors, biosensors, non-destructive testing sensors, stress sensors etc.     

Effects of Electrolytic Current Density on Structural, Magnetic Properties and GMI Behavior in Electrodeposited Bilayer FeNi/Cu Composite Wires

In this article, a systematic study has been performed on structural, magnetic properties and the GMI effect in electrodeposited FeNi/Cu composite wires in the range of current density from j=15.9?mA/cm² to 79.5?mA/cm². Our obtained results reveal a correlation between the structure, magnetic softness, and GMI behavior in prepared wires. Among the samples investigated, the softest magnetic property (lowest coercivity) was found for the wire-sample plated at j=47.7?mA/cm², which arises from the smallest nanograin size. This results in the largest values of GMI ratio and its sensitivity of this sample, which is ascribed to the optimized domain structure with a well-defined circular anisotropy. It is worthy to note that the maximum GMI ratio and the field sensitivity reached the highest values of 90?% and 7?%/Oe for at a measuring frequency of 5 MHz. This result is very promising for developing high-performance GMI-based sensors applications. Our finding demonstrates that the changes in the surface morphology and the microstructure of prepared wires has led to modification of the surface magnetic properties, and hence GMI effect.     

Perpendicular GMI Effect in Meander NiFe and NiFe/Cu/NiFe Film

We have evaluated the perpendicular giant magnetoimpedance effect (GMI) in both NiFe and NiFe/Cu/NiFe films with meander geometry in the $>$1 MHz high-frequency range. With the magnetic field, the perpendicular GMI effect shows an intense GMI peak value at a certain field. This effect is comparable to the longitudinal GMI effect in both profile and peak value amplitude. The experimental results correspond well with the predictions of a single-domain rotational magnetization model. These findings demonstrate that the deflection of the anisotropy to a perpendicular direction plays an important role in the perpendicular GMI effect.      

Equivalent Magnetic Noise Limit of Low-Cost GMI Magnetometer

We present a noise analysis of a giant magnetoimpedance (GMI) sensor using a peak detector at the optimal magnetic field working bias point of a sensor wire, by considering internal noise sources (intrinsic GMI device associated noise sources and conditioning electronic noise sources). An expression is obtained for the theoretical expected noise for known electronic design parameters and physical characteristics of the GMI wire. The most significant contributions to noise in a GMI measurement, using two basic oscillators (either a simple discrete RC oscillator or quartz oscillator) along with a peak detector, are presented. We discuss the expected extrinsic equivalent magnetic noise limit.      

Enhancement of the giant magnetoimpedance effect and its magnetic response in ion-irradiated magnetic amorphous ribbons

The influences of N and Xe ion irradiation on the giant magnetoimpedance (GMI) effect and its magnetic response in Co₆₉Fe_4.5Al_1.5Si₁₀B₁₅ amorphous ribbons were systematically investigated. A large enhancement of the GMI effect and its magnetic response were achieved in N and Xe ion-irradiated amorphous ribbons. At a frequency of 3 MHz, the GMI ratio and magnetic response for an N-ion-irradiated amorphous ribbon respectively reached the highest values of 130% and 13%/Oe, while for a non-irradiated amorphous ribbon they were only about 53% and 8%/Oe. The enhancement of the GMI effect and magnetic response in the ion-irradiated amorphous ribbons resulted from the enhancement of the permeability due to rotational magnetization. Our studies indicate that low energy ion irradiation is useful for improving the magnetic softness, GMI and magnetic response of amorphous alloys, which is of practical importance for the development of high-performance magnetic sensors.     

制备态(Fe88Zr7B5)100-xCux非晶薄膜的磁特性和巨磁阻抗

采用射频溅射法在单晶Si衬底上制备了Fe88Zr7B5)100-xCux(x=0、1、2、3、4)非晶薄膜样品,对其软磁特性和巨磁阻抗(GMI)变化行为进行了测量和研究。测量结果显示,加入适量Cu元素(x=3)的制备态样品具有极好的软磁性能和GMI效应,此样品的矫顽力仅有56A/m,在13MHz的频率下,最大有效磁导率(μe)比和GMI比分别为42.5%和17.0%。研究发现,制备态样品的电阻R、电抗X和阻抗Z都随Cu含量的增加而下降。X=0、4两个样品的μe、R、X、Z对外加磁场响应极不敏感,只有软磁性能优异的x=3样品的μe、R、X、Z才显示出对外加磁场响应敏感,因而有显著的GMI效应。样品拥有高的磁导率、小的矫顽力和低的电阻率是获得大GMI效应的本质条件。     

From Manipulation of Giant Magnetoimpedance in Thin Wires to Industrial Applications

We present results on our studies of soft magnetic properties and Giant magnetoimpedance, GMI, effect in thin microwires at elevated frequencies paying special attention to tailoring the GMI effect and achievement of high GMI effect with low hysteretic behavior. We measured magnetic field, H, dependence of real part, of the longitudinal wire impedance up to frequency, f, 4 GHz in Co-rich microwires. Amorphous microwires of appropriate composition exhibit extremely soft magnetic properties with low coercivity (generally below 10 A/m) with well defined magnetic anisotropy field, H _k . We report a number of interesting for sensor applications phenomena such as stress-impedance effect and stress sensibility of overall hysteresis loop shape. Field dependence of the off-diagonal voltage response of pulsed GMI effect in nearly-zero magnetostriction (λ _s≈?3×10^?7) microwires exhibits anti-symmetrical shape, suitable for industrial applications. We observed that the magnetic field dependence of GMI ratio can be tailored either controlling magnetoelastic anisotropy of as-prepared microwires or by heat treatment. Composite character of such microwires results in the appearance of additional magnetoelastic anisotropy. We found that if the surface anisotropy is not circumferential, then the magnetization, and consequently, the MI curve Z(H) present hysteresis. This hysteresis can be suppressed by application of sufficiently high DC bias current I _B that creates a circumferential bias field H _B.     

Enhanced giant magnetoimpedance effect in FINEMET/TiO2 composite ribbons

In order to study the influence of semiconductors on the magnetic properties and giant magnetoimpedance effect of FINEMET ribbon, titanium dioxide coating layer with different thickness was sputtered onto the free surface of the FINEMET ribbon by RF magnetron sputtering to prepare the FINEMET/TiO₂ composite ribbons. The morphology, magnetic properties, and giant magnetoimpedance of the FINEMET/TiO₂ composite ribbons were analyzed. The results show that the GMI ratio of composite ribbons first increases and then decreases with the increase of TiO₂ layer thickness (0?~?150 nm). When the thickness of TiO₂ thin film is 100 nm, the GMI ratio reaches the maximum 57.3%, which indicates that a certain thickness of TiO₂ thin film can significantly improve the GMI effect. The result can be explained by the combined result of electromagnetic interaction and stress between TiO₂ thin film and the FINEMET ribbon.

     

Microwave properties of ferromagnetic nanostructures

A review of the dynamic properties of nanostructured ferromagnetic materials at microwave frequencies (1-40 GHz) is presented. Since some confusion has recently appeared between giant magnetoimpedance (GMI) and ferromagnetic resonance (FMR), a detailed analysis is made in order to establish their differences. A brief review of a novel microwave absorption mode, the low-field microwave absorption (LFA) is then presented, together with a discussion about its similarities with GMI. Recent results on high-frequency measurements on nanogranular thin films and FMR in nanowire arrays are finally addressed.     

Enhancement of GMI Effect in Silicon Steels by Furnace Annealing

The ratio and sensitivity of giant magnetoimpedance(GMI)in grain oriented silicon steels(Fe-4.5%Si)are improved after furnace annealing in air for 20 min.By annealing at 800-C,the GMI sensitivity rises from 1.29%/Oe to 1.91%/Oe and the ratio increases from 237%to 294%with decreasing characteristic frequency. The results are attributable to an increase in the transverse magnetic permeability during the heat treatment. From simulation by finite element method,the GMI effect can be interpreted as the modificat...     

Giant Magnetoimpedance Current Sensor With Array-Structure Double Probes

We have designed a novel giant magnetoimpedance (GMI) noncontact current sensor with array structure double probes. Unlike previously reported sensors, our sensor's probes consist of many pieces of commercial amorphous ribbons, which are parallel to each other, equidistant, and connected in series, and a permanent magnet provides a bias magnetic field. The double-probe output shows the best sensitivity and linearity at a bias magnetic field of 7.40 Oe. Under this field, the sensor shows sensitivity of 1 V/A in the current range of plusmn3 A, measurement precision of less than 0.15% at room temperature, and good thermal stability in the temperature region between -20degC and 30degC.     

Effects of thickness and heat treatments on giant magnetoimpedance of electrodeposited cobalt on silver wires

We studied the effects of thickness and heat treatments on giant magnetoimpedance (GMI) of cobalt-coated silver wires from 1 kHz to 100 MHz, under axial static magnetic field of 2 kOe. Cobalt, of thickness ranging from 1 to 25 /spl mu/m, was electro-deposited on 47.7-/spl mu/m-diameter silver wires. The frequency dependence of GMI varied with cobalt thickness with a maximum of 176% in 10-/spl mu/m-thick cobalt at the characteristic frequency 2 MHz. The characteristic frequency decreased with increasing thickness of cobalt layer but it was rather insensitive to dc Joule heating and conventional furnace annealing. However, both heat treatments led to magnetic hardening and decrease in GMI ratio. Joule heating also induced anisotropy in wire structures normally dominated by axial anisotropy.     

The effect of magnetic field orientation on the magnetoimpedance of electroplated NiFeCo/Cu wire

Journal of Materials Science: Materials in Electronics - Giant magnetoimpedance (GMI) effect in electrodeposited NiFeCo/Cu wire is studied in the intermediate frequency region...     

FeSiB薄膜的巨磁阻抗和应力阻抗效应研究

软磁材料中存在巨磁阻抗 (giantmagneto impedance ,GMI)效应以及与之相同来源的应力阻抗 (stress impedance ,SI)效应 ,利用这两种效应可以制成具有高灵敏度的微型化的磁场和应力 应变传感器。本文基于传感器的实际应用 ,对图形化的、较大磁致伸缩的FeSiB单层和多层薄膜的巨磁阻抗和应力阻抗效应中频率和退火的影响进行了研究。结果表明 ,对于两种效应 ,经过退火处理的单层和多层膜均可在较低的频率下得到较高的灵敏度 ,而多层膜中的应力阻抗效应将为新型高灵敏传感器的设计和研制开辟一条崭新的途径     

Improvement of Giant Magnetoimpedance and Sensitivity in Co68.5-xFe4WxSi16.5B11 (x = 0.8, 2) Ribbons Sandwiched in PVA/Fe3O4 Nanocomposite Films

Journal of Superconductivity and Novel Magnetism - In this work, giant magnetoimpedance (GMI); magnetic hysteresis loop; and sensitivity of Co68.5Fe4Si16.5B11 (S), Co67.7Fe4W0.8Si16.5B11 (W1), and...     

Giant Magnetoimpedance Current Sensor With Spiral Structure Double-Probe

A novel giant magnetoimpedance (GMI) noncontact current sensor with spiral structure double-probe is designed. Differing from the formerly reported sensors, the probes of this sensor consist of annealed commercial amorphous ribbons which are curled to spiral tubes. Two couples of permanent magnets are applied to provide bias magnetic field. The distance between the probes and the permanent magnets is fixed at 2.4 cm. The sensor shows sensitivity of 1 V/A in the current range of $pm$ 1.5 A, measurement precision of less than 0.16% at room temperature, and good thermal stability in the temperature range between $-$20 and 30 $;^{circ}{rm C}$.      

High frequency magnetic behavior through the magnetoimpedance effect in CoFeB/(Ta, Ag, Cu) multilayered ferromagnetic thin films

We investigate the structural and magnetic properties and the magnetoimpedance effect of CoFeB/(Ta, Ag, Cu) multilayered thin films grown by magnetron sputtering. It is noticed that the peak of maximum magnetoimpedance ratio values for a given frequency, as well as its position in frequency, is varied according to the used non-magnetic metal. For the CoFeB/Ta and CoFeB/Ag multilayered films, peaks of 30% and 27%, respectively, are observed at localized frequency ranges. For the CoFeB/Cu multilayer, slightly smaller values are verified, but for a wide frequency range. The magnetoimpedance results are analyzed in terms of the mechanisms responsible for the impedance variations at different frequency ranges and the magnetic and structural properties of the multilayer.     

Ferromagnetic microwires enabled polymer composites for sensing applications

In the present work, sensing functionalities are introduced into structural composites via embedded magnetic microwires. A systematic study on the structure and functionalities of microwires and their composites is performed. The single-wire composite shows a significant giant magnetoimpedance (GMI) effect of up to 320% in a frequency range of 1–100 MHz due to stress enhanced transverse magneto-anisotropy. With increasing quantities of embedded wires from 1 to 3, the maximum GMI ratio is enhanced significantly by more than 35%, making the resultant composite favourable for field sensing applications. The microwire-composite also shows superior stress-sensing resolution as high as 134.5 kHz/microstrain, which is about 26 times higher than the recently proposed SRR-based sensor. As evidenced by the structural examination and tensile tests, the extremely small volume fraction of microwires (～0.01 vol.%) allows the wire-composites to retain their mechanical integrity and performance.