NiFeCoP/BeCu复合结构丝的巨磁阻抗效应和磁化频率特性

用化学镀的方法制备了NiFeCoP/CuBe复合结构丝，研究了其巨磁阻抗特性.结果表明复合结构丝在较低频率的驱动电流下就有明显的磁阻抗效应，当驱动电流频率在20kHz时的磁阻抗效应为40％，最大磁阻抗效应出现的频率在180kHz，为97％.利用复数磁导率和等效电路探讨了该复合丝铁磁层磁化过程的频率特性，复合结构丝的特征弛豫频率在1MHz左右.外加直流磁场抑制畴壁移动，在等效电路中与抵消部分并联电路相关. 关键词： 巨磁阻抗效应 磁导率 弛豫频率 等效电路     

Magnetic properties of electroplated wires coated by ferrofluid

Low-frequency magnetic properties of ferromagnetic composite wires were studied with and without coating by ferrofluid. Non-magnetic CuBe wires of 0.1 mm diameter were electroplated with FeCoNi layer of 1 μm thickness. Magnetization curves were measured in the frequency range of 10 Hz–3 kHz. The composite CuBe/FeCoNi/ferrofluid material shows a hysteretic behaviour in a small field. The hysteresis loop of ferrofluid covered electroplated wire is not a simple sum of the ferrofluid “wire” plus non-covered wire signals. It indicates an interaction between magnetic wire and ferrofluid which can be revealed by low-frequency measurements. The combination “electroplated wire/ferrofluid” can be considered as a new type of composite magnetic material consisting of solid magnetic core coated by complementary liquid magnetic material. Low-frequency measurements in presence of ferrofluid can be a useful method to study magnetic properties of ferromagnets.     

Intermittent deposition and interface formation on the microstructure and magnetic properties of NiFe/Cu composite wires

In this work, magnetron sputtering in the form of continuous deposition or intermittent deposition modes was used to obtain NiFe/Cu composite wires. Based on the results, intermittent deposition mode led to the formation of an interface between deposited layers. A better crystallite and a little grain growth were found for the intermittently deposited wire. Good soft magnetic properties and large giant magneto-impedance (GMI) effect were exhibited by both composite wires. The GMI profile for the intermittently deposited composite wire was characterized by two peaks, which could be attributed to the difference in the magnetic properties of the inner and the outer magnetic layers. Annealing was introduced to the intermittently deposited wire so that the inherent stresses were partially relaxed. As a result, its GMI effect was enhanced and the magnetic properties of the two magnetic layers became similar. Hysteresis loops of the composite wires displayed different magnetic behaviors and hence further affirmed the GMI results.     

Cytotoxicity and GMI bio-sensor detection of maghemite nanoparticles internalized into cells

In this work we determine conditions to produce cell samples for imaging with detection of the modification of the magnetic field by maghemite (Fe₂O₃) nanoparticles acting as a high sensitivity magnetic bio-sensor based on the giant magneto-impedance (GMI) effect. Mat Ly Lu cells are grown for 24 h with various maghemite nanoparticles concentrations (from 0 to 6 mg/ml). The percentage of viable cells is determined by counting labeled cells with trypan blue under an optical microscope. The quantity of nanoparticles internalized into the cells is evaluated by X-ray fluorescence analysis and expressed in iron moles per cell. The GMI bio-sensor was tested with the various samples. We observed that the best sensitivity of the GMI bio-sensor was obtained at a frequency of 1 MHz. To confirm these results in the presence of cell samples, four measurement frequencies were pre-selected (from 1 to 100 MHz) and tested. Cell growth conditions compatible with an acceptable percentage of cell viability for various concentrations of nanoparticles were also determined. These experiments allow us to conclude that cell growth with 0.1 mg/ml of nanoparticles for 24 h shows modifications of the magnetic field detectable optimally at 1 MHz frequency.     

Giant magneto-impedance and skin effect in CuBe/CoNiP composite wires

The giant magneto-impedance and skin effect in electroless deposited CuBe/CoNiP composite wires with different diameter of CuBe core are presented, and involves a theoretical approach of the current density distributions in layers. Results show that the strong eddy current in the magnetic CoNiP coating will be induced due to the electromagnetic interactions with the CuBe core. It makes the skin effect strong in the magnetic coating even at very low frequency, and at this, large MI changes can also be observed.     

Longitudinally driven giant magneto-impedance effect enhancement by magneto-mechanical resonance

Longitudinally driven giant magneto-impedance (GMI) effect in amorphous magnetostrictive Fe₂₄Co_11.82Ni_47.3Si_1.47B₁₅ ribbons was investigated. The experimental results showed that the magneto-mechanical resonance of the ribbons had significantly enhanced GMI effect. The strong magneto-mechanical coupling (MMC) interaction resulted in high MI ratio. Maximal GMI ratio of 1532% was obtained in the sample annealed at 340 °C under transverse magnetic field. The results are explained in terms of MMC and resonance of the magnetostrictive materials.     

外磁场与带轴夹角对非晶FeSiB/Cu/FeSiB三明治薄带巨磁阻抗特性的影响

采用层间胶合方法制备了淬态非晶FeSiB/Cu/FeSiB三明治薄带,研究了同尺寸单层薄带和三明治薄带的巨磁阻抗(giant magneto-impedance, GMI)随外磁场与带轴夹角β的变化特性.结果表明,FeSiB单层薄带在7.0 MHz最佳响应频率下,GMI仅约30%,外磁场与带轴夹角对单层薄带GMI几乎没有影响;三明治薄带的GMI效应则十分显著,在0.6 MHz最佳响应频率下,纵、横向GMI比分别达到272%和464%, GMI随β的增大而增强;所有β角的三明治薄带GMI曲线都出现各向异性峰,各向异性峰随β的增大而展宽.根据磁畴转动模型推导了薄带横向磁导率与各向异性场及β之间的函数关系式.结果显示,三明治薄带GMI随夹角β变化的特性与理论推算的横向磁导率变化有较好的一致性,而单层薄带则不然.该磁畴转动模型能定性解释三明治薄带GMI随外磁场方向变化特性.     

Soft magnetic properties and giant magneto-impedance effect of Fe73.5−xCrxSi13.5B9Nb3Au1 (x=1–5) alloys

In this paper, the effect of microstructural and surface morphological developments on the soft magnetic properties and giant magneto-impedance (GMI) effect of Fe_73.5−xCr_xSi_13.5B₉Nb₃Au₁ (x=1, 2, 3, 4, 5) alloys was investigated. It was found that the Cr addition causes slight decrease in the mean grain size of α-Fe(Si) grains. AFM results indicated a large variation of surface morphology of density and size of protrusions along the ribbon plane due to structural changes caused by thermal treatments with increasing Cr content. Ultrasoft magnetic properties such as the increase of magnetic permeability and the decrease of coercivity were observed in the samples annealed at 540 °C for 30 min. Accordingly, the GMI effect was also observed in the annealed samples.     

Microwire array for giant magneto-impedance detection of magnetic particles for biosensor prototype

A new giant magneto-impedance (GMI) biosensor prototype based on a glass-coated microwires array is reported. The optimal measurement conditions and the influence of a liquid suspension of commercially available polymer-based magnetic microparticles on the magneto-impedance (MI) response of the array were studied. The relative change in MI response enlarges as the number of the active microwires increases. The highest variation of 35% was found for 10 active microwires, for a current intensity of 10 mA. Some possible applications of the biosensor prototype are outlined.     

Finite element method calculations of GMI in thin films and sandwiched structures: Size and edge effects

The impedance values of magnetic thin films and magnetic/conductor/magnetic sandwiched structures with different widths are computed using the finite element method (FEM). The giant magneto-impedance (GMI) is calculated from the difference of the impedance values obtained with high and low permeability of the magnetic material. The results depend considerably on the width of the sample, demonstrating that edge effects are decisive for the GMI performance. It is shown that, besides the usual skin effect that is responsible for GMI, an “unexpected” increase of the current density takes place at the lateral edge of the sample. In magnetic thin films this effect is dominant when the permeability is low. In the trilayers, it is combined with the lack of shielding of the central conductor at the edge. The resulting effects on GMI are shown to be large for both kinds of samples. The conclusions of this study are of great importance for the successful design of miniaturized GMI devices.     

射频溅射功率对FeZrBCu软磁合金薄膜巨磁阻抗效应的影响

用射频溅射法制备了FeZrBCu软磁合金薄膜.研究了不同溅射功率对FeZrBCu薄膜软磁特性和巨磁阻抗效应的影响.用电子探针显微镜测量发现，当溅射功率为240W时，薄膜样品中Fe的原子含量为8732%，Cu的原子含量为29%.这种样品的矫顽力最小，为68A/m，饱和磁化强度约为111×105⁵A/m，软磁性能最佳，巨磁阻抗效应最大，溅态膜在 13MHz最大巨磁阻抗比纵向为17%，横向为11%.重点分析了阻抗的电阻、电感分量及横向有 效磁导率随频率的变化，得到在低频下主要是磁电感 关键词： 铁基合金 薄膜 巨磁阻抗效应     

FeCuCrVSiB单层和多层膜的横向巨磁阻抗效应

用射频溅射法制备了Fe_71.5Cu₁Cr_2.5V₄Si₁₂B₉单层膜和结构为(F/S)₃/M/(F/S)₃的多层膜，在制备过程中加72kA/m的纵向磁场.研究表明在制备过程中加磁场明显改善了材料的软磁性能，降低了材料的矫顽力.将样品经不同温度退火热处理后，发现经230℃退火1.5h的单层膜和多层膜具有最佳的软磁性能和最大的磁阻抗效应，单层膜最大横向磁阻抗比为37.5%，多层膜最大横向磁阻抗比高达277%.通过比较单层和多层膜磁阻抗效应随频率和磁场的变化，发现多层膜具有较低的磁阻抗效应的临界频率和峰值特征频率，和较大的磁阻抗变化率，而且有较低的横向磁阻抗效应的饱和场. 关键词： 铁基合金 多层膜 巨磁阻抗效应     

横向偏置场作用的非晶带巨磁阻抗效应理论

采用多畴结构模型,考虑非晶带具有180°畴壁的磁畴及其两面的偏置磁场方向的不同,根据自由能最小原理,Maxwell方程组及带阻尼项的Landau-Lifshitz方程,建立了非晶态合金带在横向偏置磁场作用下的巨磁阻抗效应的理论计算公式. 提出并采用四状态平均磁导率代替单畴模型获得的磁导率,得到了更符合实际的处于偏置场作用的阻抗随外磁场变化的理论结果. 关键词： 偏置磁场 四状态 多畴结构 巨磁阻抗     

Magneto-Impedance behavior of Co-Fe-Nb-Si-B-based ribbons

The giant magneto-impedance of melt spun Co_xFe_72−xNb₄Si₄B₂₀(x=10, 20, 36, 50) amorphous and nanostructured ribbons have been investigated. Alloys have been optimized at the driving current amplitude, frequency and found that amorphous ribbon of nominal composition of Co₃₆Fe₃₆Nb₄Si₄B₂₀ shown maximum GMI ratio of 13%. The behaviour of the driving current amplitude on the GMI behaviour was studied and the sample was optimized for driving current amplitude, I_ac=10 mA. The frequency dependence of the GMI behaviour was studied for the ribbon sample Co₃₆Fe₃₆Nb₄Si₄B₂₀ at frequency in the range of 100 kHz-1.2 MHz of the optimized driving current amplitude and it was found that the sample showed the maximum GMI behaviour at f=700 kHz. The optimized samples were Joule heated at the current density J=0-35 A/m² for a period of 1 min. The GMI ratio initially increased then progressively deteriorated with J, but after a certain range it shows up to 16% of improvement in the magneto-impedance value due the increase of nanocrystalline volume fraction. The asymmetry in the GMI profile was observed for the sample Joule heated at J=1-5 A/m² for 1 min.     

磁场退火对Co基熔体抽拉丝巨磁阻抗效应的影响

对Co基熔体抽拉非晶丝进行了普通炉内退火和不同磁场强度（500 Oe,1600 Oe,4000 Oe）下的横向和纵向磁场退火,利用HP4192阻抗分析仪和Lakeshore7407VSM分析了退火态样品的巨磁阻抗（GMI）效应和软磁性能.研究结果表明,纵向磁场降低了环向各向异性,纵向磁场退火样品GMI效应降低且GMI曲线为单峰,最大阻抗变化率ΔZ/Z为131%,磁场响应灵敏度为7%/Oe;而横向磁场提高了环向畴体积,增加了环向各向异性场,导致退火样品GMI曲线随频率升高由单峰转 关键词： 非晶丝 巨磁阻抗效应 退火     

Feedback-type giant magneto-impedance sensor based on longitudinal excitation

In this paper, the characteristics of Fe-based amorphous ribbon based on the longitudinal excitation are investigated with assistance of the theory of the giant magneto-impedance (GMI) effect. A feedback-type GMI micro-magnetic sensor is designed with regard to the design of the sensing element, the excitation circuit, the conditional circuit and the feedback circuit. With the analysis of the dynamic and static characteristics of the feedback-type GMI sensor, it is concluded that the designed feedback-type GMI sensor has higher linearity, stability and dynamic characteristics than non-feedback-type GMI sensor in −2.5 to +2.5 Oe.     

Enhancement of giant magneto-impedance effect in Ni80Fe20/SiO2/Cu composite wires

Ni₈₀Fe₂₀/SiO₂/Cu composite wires of Cu core 60 μm in diameter and coated with layers of SiO₂ and Ni₈₀Fe₂₀ were prepared by RF magnetron sputtering. The influences of the insulator layer thickness, the measurement mode and the magnitude of the driving current on the giant magneto-impedance (GMI) effect were investigated. The results showed that there was an optimum thickness of the insulator layer and the driving current can influence the shape of the MI curve. Resonance enhancement of the GMI was found in the new measurement mode. The results are discussed by taking account of the electromagnetic interactions.     

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.     

FeCuCrVSiB多层膜巨磁阻抗效应的研究

研究了结构为 (FM/SiO₂)₃/Ag/(SiO₂/FM)₃ 多层膜的巨磁阻抗(GMI)效应（这里的F M≡FeCuCrVSiB）．多层膜采用射频溅射法沉积在单晶Si衬底上，沉积过程中，沿膜面长方 向施加约72kA/m的磁场，然后在不同的温度下对样品进行了退火处理．结果表明，该多层膜 样品即使在沉积态便具有相当好的软磁性能和GMI效应，在7MHz的频率下，最大纵向和横向 巨磁阻抗比分别为45%和44%．在230℃下经90min退火处理后的样品具有最佳的GMI效应，在85MHz的频率下，最大纵向和横向巨磁阻抗比分别达到251%和277%．与磁性层总厚度相同的FeCuCrVSiB/Ag/FeCuCrVSiB三层膜相比较，在这种多层结构中出现的GMI效应更强． 关键词： 多层膜 巨磁阻抗效应 趋肤效应 有效磁导率     

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.