同轴电缆结构复合丝巨磁阻抗效应的研究

采用脉冲电沉积工艺在直径为200μm的铜丝表面沉积铁镍合金镀层,形成具有同轴电缆结构的巨磁阻抗复合丝材料。分别改变复合丝磁性外壳厚度与铜丝直径,研究复合丝结构对巨磁阻抗效应的影响。发现巨磁阻抗比值随磁性外壳厚度的增大及铜丝直径的增大而增大,特征频率则向低频端移动。本文还发现在外加直流磁场低于5．57kA／m时,驱动交流电幅值增大,巨磁阻抗效应增大;高于5．57kA／m时,驱动交流电幅值的大小几乎不再影响复合丝的巨磁阻抗效应。在驱动电流上叠加20mA以下的直流偏置对巨磁阻抗效应没有影响。     

Giant Magnetoimpedance Effect: Concept and Prediction in Amorphous Materials

Giant magneto impedance (GMI) effect was experimentally measured on as-cast, post-production and coated with chemical technique amorphous wire and ribbon materials consisted of varied chemical composition over a frequency range from 0.1 to 8 MHz under a static magnetic field between ?8 and +8 kA/m. The results show that each amorphous sample has a certain operational frequency for which the GMI effect has maximum magnitude and the other parameters such as annealing and coating have a significant influence on the GMI effect. It is believed that the domain structure and wall mechanism in the material are responsible for this behaviour. A 3-node input layer, 1-node output layer artificial neural network (ANN) model with three hidden layers including 30 neurons and full connectivity between the nodes was developed. A total of 1600 input vectors obtained from varied treated samples was available in the training data set. After the network was trained, better results were obtained from the network formed by the hyperbolic tangent transfer function in the hidden layers, there was a sigmoid transfer function in the output layer and we predicted the GMI. Comparing the predicted values obtained from the ANN model with the experimental data indicates that a well-trained neural network model provides very accurate results.     

高磷含量CoP-Cu复合丝巨磁阻抗效应的频谱特性

控制电化学工艺条件在直径为200μm的铜丝表面合成CoP磁性镀层成功地制备出高磷含量CoP—Cu复合丝巨磁阻抗效应材料。当磷含量为20%（原子分数）时,复合丝巨磁阻抗效应非常显著,达80%以上。本文详细研究了复合丝材料的频谱及巨磁阻抗效应频谱,指出复合丝巨磁阻抗具有较低的特征频率及较宽的频率使用范围与此新型结构有关,本文还发现,随频率的增加,最大负巨磁阻抗比对应的外加直流磁场也在增加,并且在高频与低频时,巨磁阻抗效应随磁场的响应曲线明显不同。     

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。     

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     

应力作用下电流退火对钴基非晶薄带的巨磁阻抗效应的影响研究

采用应力作用下的直流电流退火处理Co68.2Fe2.3Mo2Si12.5B15非晶薄带，详细讨论了应力退火前后Co基薄带的巨磁阻抗效应的变化，以及退火时间对巨磁阻抗效应的影响，研究表明：应力作用下的电流退火有利于巨磁阻抗效应的提高，并可以通过控制退火时间控制阻抗与外场变化关系曲线形状。     

三明治结构FeNi/Cu/FeNi多层膜巨磁阻抗效应研究

采用MEMS技术在玻璃基片上制备了三明治结构FeNi/Cu/FeNi多层膜,在1～40 MHz范围内研究了FeNi/Cu/FeNi多层膜中的巨磁阻抗效应特性.当磁场Ha施加在薄膜的长方向时,巨磁阻抗效应随磁场的增加而增加,在某一磁场下达到最大值,然后随磁场的增加而下降到负的巨磁阻抗效应.在频率为5MHz时,巨磁阻抗效应在磁场Ha=800 A/m时达到最大值26.6%.巨磁阻抗效应的最大值及负的巨磁阻抗效应与多层膜中磁各向异性轴的取向及发散有关.另外,当磁场施加在薄膜的短方向时,薄膜表现出负的巨磁阻抗效应,在频率5 MHz、磁场Ha=9600 A/m时,巨磁阻抗效应可达-15.6%.     

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.      

AC susceptibilities of conducting cylinders and their applications in electromagnetic measurements

We present accurate calculations and tabulations of the volume and midplane-averaged complex ac susceptibilities of nonmagnetic conducting cylinders with aspect ratio ranging from 0.1 to 10 as functions of a dimensionless frequency. We discuss their features in terms of eddy-current demagnetizing effect. We explain their applications in high-sensitivity, low-temperature, and high-field ac susceptometers and contactless conductivity measurements.     

软磁薄带巨磁阻抗效应的数值分析

利用磁畴壁移动模型以纳米晶软磁合金Ｆｅ７３．５Ｃｕ１Ｎｂ３Ｓｉ１３．５Ｂ９为例对软磁薄带中的巨磁阻抗效应进行了数值分析，结果发现不同的磁导率机制并不能显著发迹巨巨磁阻抗效的大小仅由磁导率对外加磁场的敏感性决定，从趋肤深度的角度讨论了巨磁阻抗效应的频率特性。     

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.     

Structural and magnetic studies on the enhancement of the giant magnetoimpedance by ion irradiation

The mechanism of abrupt increase of the giant magneto impedance (GMI) ratio in the ion irradiated Co-based amorphous ribbon has been investigated. The grazing incident X-ray diffraction and transmission electron microscope were used to characterize the samples before and after ion irradiation. The GMI-ratio considerably increased in the ion irradiated samples and the GMI response showed strong dependence on the driving frequencies. The Barkhausen noise (BN) signals are increased for the Ar ion irradiated sample with dose of 1 × 10¹⁷ ion/cm². The results are interpreted in terms of GMI variation associated with domain wall dynamics.     

Slots vs. cracks in eddy current NDE

The thin-skin theory of Lewis, Michael, Lugg, and Collins (LMLC) is applied to an analysis of the effects of slot closure on eddy current response. The LMLC model is shown to lead to a relatively simple expression for the ratio of the impedance change for an open slot to the impedance change for a closed slot, which represents a crack. Numerical calculations for a nonmagnetic material show that the impedance ratio is an almost linear function of the slot opening in skin depth units, and is relatively insensitive to slot length and aspect ratio. For ferromagnetic materials with large relative permeability, there is no significant slot closure effect. LMLC calculations are supplemented by volume integral calculations at low frequencies where the thin-skin theory fails.     

Co—Fe—Si—B非晶丝的巨磁阻抗效应研究

用旋转水中纺丝法制成几种不同直径的（Ｃｏ０．９４Ｆｅ０．０６）７２．５Ｓｉ１２．５Ｂ１５非晶丝,对丝进行张力退火后,测试了非晶丝热处理前后的磁阻抗性能。结果表明制成的非晶丝具有明显的巨磁阻抗效应,且巨磁阻抗效应随电流频率不同而表现出正磁阻抗和负磁阻抗两种规律。张力退火对正磁阻抗效应有明显改善,而且对直径小的试样,阻抗对轴向外磁场变化的灵敏度更高。实验得到的最大灵敏度为１２４％／Ｏｅ。     

纳米晶FeCuNbSiB多层膜的巨磁阻抗效应研究

研究了纳米晶态下Fe73.5Cu1Nb3Si13.5 B9多层膜的巨磁阻抗(GMI)效应。研究结果表明纵向巨磁阻抗(LMI)效应在3MHz时取得最大值为44％,横向巨磁阻抗(TMI)效应在6MHz时取得最大值为46％。LMI与TMI随外磁场有不同的变化行为,TMI曲线具有阁值行为,超过阈值磁场后出现明显的磁阻抗效应。晶化后出现最大值阻抗效应所对应的频率下降,由非晶态下的13MHz下降为晶化后的3MHz。薄膜样品的磁阻抗效应与样品中磁矩的空间分布密切相关．磁矩垂直面向分布时。磁阻抗效应下降为5％     

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.     

软磁薄膜高频巨磁阻抗效应的理论模型

利用修正的Landau-Lifshitz-Gilbert方程,对横向单轴磁各向异性软磁薄膜在高频下的有效横向磁导率做了理论推导,从而得到了关于薄膜高频阻抗的理论表达式,并与其它理论结果作了比较。结果表明,给出的有效横向磁导率表达式与其它理论结果一致。详细讨论了小尺寸薄膜中退磁场对共振频率的影响,理论计算与实验结果相符合。     

铁磁层/导电层/铁磁层多层膜中巨磁阻抗效应理论*

采用经典电磁理论,对铁磁层／导电层／铁磁层（M／C／M）多层膜中出现的巨磁阻抗效应进行了理论分析。对于单轴横向磁各向异性多层膜,理论计算结果表明：高频阻抗在某一外加磁场（近似等于等效各向异性场）下出现最大值,铁磁层和导电层电阻率相关较大的多层膜中将出现较强的巨磁阻抗效应。多层膜在1MHz附近即可出现远大于单层膜的阻抗变化比。多层膜理论计算与实验结果能够较好地符合。     

Cu对NiFe/Cu/NiFe层状薄膜的巨磁阻抗效应影响的研究

用直流磁控溅射方法制备了NiFe/Cu/NiFe层状薄膜 ,研究了Cu膜宽度对NiFe/Cu/NiFe层状薄膜的巨磁阻抗效应的影响 ,结果表明 ,层状薄膜的巨磁阻抗效应随Cu膜宽度发生振荡现象 ;并提出了一个等效电路模型直观地解释了层状薄膜增强巨磁阻抗效应的机理     

The shearing of perpendicular loop with columnar structure

The experimental results on the hysteresis loops of magnetic films with perpendicular anisotropy show that the loop is sheared. The shearing of the loops depends strongly on the thickness of the film. This phenomenon was never successfully explained with the particulate model. We use a simple three dimensional particulate model with an effective demagnetizing field to calculate the slope of the perpendicular loops. The calculated results are compared with the experimental results for the CoCr sputtered films. By considering different separation distance of the columns, good agreement is obtained between the calculations and the experimental data for the shearing of the loop.