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。     

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.     

电流退火对CoFeSiB非晶丝和薄带的巨磁阻抗效应比较

采用熔融抽拉法和单辊急冷法分别制备了Co68.25Fe4.5Si12.25B15非晶丝和薄带。测量了制备态下两者的巨磁阻抗(GMI)效应,发现非晶丝的GMI比率高于薄带。研究了不同电流密度退火后非晶丝和薄带的GMI效应,结果发现ΔΖ/Ζ=[Z(H)-Z(H=0)]/Z(H=0)都明显上升,且非晶薄带数值更大;当电流密度等于0.96×107A/m2时,薄带的这一比率最大达到410%,磁场灵敏度达到5.1%/(A/m)。分析了出现上述现象的原因。     

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.     

Study of Giant Magneto-Impedance Behavior in Co-Fe Based Amorphous/Nanocrystalline Materials

Giant magneto-impedance (GMI) behavior have been studied in melt spun Co_71-XFe_XCr₇Si₈B₁₄ (X = 0, 2, 3.2, 4, 6, 8, and 12 at%) alloys. The addition of Fe in the system changed the saturation magnetostriction constant from negative to positive values. The GMI property was measured with a driving current of 5 mA and 4 MHz frequency using a spectrum analyzer. The GMI ratio increased with the increase of the applied dc field and became maximum at a field H_k known as the anisotropy field of the materials. The maximum of GMI ratio (GMI_max) depended on the Fe content and was maximum (12%) for Fe = 4 at% for the alloys in the as-melt spun state. Substantial increase of GMI_max to 66% for Fe = 4 at% was observed after annealing the sample at 673 K.     

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.     

磁控溅射法制备IrMn底钉扎自旋阀研究

采用高真空直流磁控溅射的方法,在玻璃衬底上制备了结构为Ta／buffer layer／IrMn／CoFe／Cu／CoFe／NiFe／Ta的IrMn底钉扎自旋阀。研究了NiFe和Cu作为缓冲层对自旋阀磁性能的影响,并对缓冲层厚度进行了参数优化,当缓冲层厚度为2nm时自旋阀各项性能达到最佳。研究了退火制度对底钉扎自旋阀性能的影响,得到了30000e强磁场下200℃保温1h为最佳处理条件。通过结构的改善和工艺的优化,得到的底钉扎自旋阀的磁电阻率8．51％,矫顽场为0．50e,交换偏置场超过8000e。最后对自旋阀的底钉扎和顶钉扎结构进行了比较。     

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%.     

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。     

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     

Magnetic properties, microstructures, and corrosion resistance ofhigh-saturation FeMoN and FeRhN films for recording heads

We have investigated high-saturation FeMoN and FeRhN films, deposited by radio frequency-diode reactive sputtering on alumina-TiC substrates, for inductive head applications. A minimum coercivity of ~1.2 Oe is obtained in (Fe_97.8Mo_2.2)N films at a N ₂/Ar flow ratio of ~6.2%. A minimum coercivity of ~1.6 Oe is obtained in (Fe_96.9Rh_3.1)N films at a N₂/Ar flow ratio of ~4.6%. The films mainly consist of α-Fe phase and γ'-Fe₄N phase; The magnetic properties of these films are stable under easy axis field annealing up to 350°C. Addition of Rh or Mo to FeN has resulted in a significant improvement in corrosion resistance over that of FeN. The localized corrosion resistance of FeRhN and FeMoN can be comparable to that of Permalloy. In contrast, their intrinsic corrosion resistance is inferior to that of Permalloy, but it can be adjusted and controlled by pH level     

Dependence of frequency and amplitude of the ac current on the GMI properties of Co based amorphous wires

The frequency and the amplitude of the driving ac current dependence of the Giant Magneto-Impedance (GMI) behaviour in (Fe₆Co₉₄)_72.5Si_12.5B₁₅ amorphous wire have been studied. The single and two-peak behaviour in the GMI characteristics are observed which depends on the amplitude and frequency of the ac driving current flowing through the sample. The GMI ratio initially increased and then decreased monotonically with the increase of frequency, f, and the amplitude of the ac current, I_ac. With the increase of amplitude of ac current, the response of the GMI voltage is found non-linear with the generation of higher harmonics. With the increase of higher harmonics, the first harmonic component of the GMI voltage started decreasing. With the increase of the ac current, the field sensitivity of the first harmonic components of the GMI voltage decreases and in higher harmonics it shows an increasing trend. The maximum field sensitivity was observed 7.5% per A/m for I_ac = 2 mA and at frequency 100 kHz. The paper investigates the response of the second and third harmonics with the frequencies and amplitude of the driving current. A voltage equation derived from the rotational model to study the response of the GMI voltage.     

The Effect of Crossed Configuration on Giant Magneto-Impedance Properties of Cobalt-Based Amorphous Wires

In this work, the impedance properties of Co_68.15Fe_4.35Si_12.5B₁₅ cobalt-based amorphous wires connected in a crossed configuration have been studied. For this purpose, at first, the magnetic properties of a single wire and also two wires perpendicular to each other were investigated. The obtained results for a single wire present a decrease and increase, respectively, in the transverse and longitudinal saturation magnetization by increasing the angle of the wire and the applied magnetic field. In the same time, the anisotropy field of a single wire shows the sinusoidal variations by increasing the angle from 0 to 90^° whereas coercivity field has the lowest value at the angle of 45^°. Furthermore, the saturation magnetization and the coercivity of two crossed wires get the highest and lowest values at the angle of 45^°. Besides, the magneto-impedance and sensitivity of two crossed wires increase from 193 % and 4.95 (1/Oe) for an angle of 0^° to 528 % and 20.05 (1/Oe) for an angle of 45^°, which is in agreement with the magnetic properties of wires. Altogether, our results show that crossed configuration of wires at an appropriate angle of magnetic field can improve the GMI response and make the samples more suitable for magnetic vector sensors.     

Deposition and Magnetic Properties of Fe3O4/Fe/Fe3O4Tri-layer Films

1. IntroductionIron oxides include several crystalline forms:hematite (or-FeZO3), magnetite (Fe3O4), maghemite(7-Felon) and wustite (FeO). They have interesting structural and magnetic properties, and are practically important in magnetic and electronic applications. The strongly ferrimagnetic 7--FeZO3 phaseearned much attention due to their applications asrecording media. The attainment of 7-FeZO3 involves complicated processing[1]. In our previousstudies, high coercivity 7-FeZO3, Fe3…     

Magnetic annealing of amorphous alloys

Amorphous alloys with nominal composition of Ni40Fe40P14B6are shown to respond to annealing in a magnetic field. Coercive forces are reduced by a factor of 10 to 50 during annealing of straight ribbons to values of 0.003 Oe, as low as ever reported for potentially useful materials. Concurrently the ratio of the magnetization in 1 Oe applied field, to saturation, increases from about 0.5 to 0.95. These changes during annealing correlate with measured stress relief changes. It thus appears that most of the strain-magnetostriction contribution to the anisotropy is removed during annealing. Magnetic annealing at temperatures as low as 100°C results in noticeable changes in properties. From measurements transverse to the magneticaliy induced anisotropy axis, the induced anisotropy is calculated to be about 800 ergs/cm³, considerably smaller than obtained in crystalline Ni50Fe50. This field-induced anisotropy is reversible in direction and magnitude by reheating the sample to its Curie temperature and then cooling in a field. Annealing of 1.5 cm diameter toroids, made from 50 μm thick tapes, increases the initial permeability by more than a factor of 10 and decreases losses by more than a factor of 10. Losses and permeabilities after heat treatment compare favorably to the Permalloys with similar saturation magnetizations.     

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.     

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.     

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％     

Preparation and Magnetic Properties of FePt Nanodot Arrays Sputtering on AAO Templates

FePt nanodot arrays are the promising recording media for future super-high density magnetic recording because of their huge uniaxial magneto-crystalline anisotropy and good signal noise ratio. In this article, FePt nanodot arrays were successfully prepared on anodic aluminum oxide (AAO) templates by magnetron sputtering, and an Ag underlayer was proposed to improve the magnetic properties of FePt nanodot arrays. The dependences of Ag underlayer, annealing temperature, and pore diameter on the magnetic properties of FePt nanodot arrays were investigated. Using the AAO templates with pore diameter of 80 nm and annealing temperature of 600°C, the coercivity of Ag/FePt nanodot arrays is improved significantly to 10262 Oe.