Giant magnetoimpedance in amorphous (Co0.93Fe0.7)63Ni10Si11B16 glass-coated microwire

Giant magnetoimpedance (GMI) effect has been measured in a glass-coated amorphous (Co_0.93Fe_0.7)₆₃Ni₁₀Si₁₁B₁₆ microwire as a function of DC magnetic field and up to the frequency of 11 MHz. The sample shows single peak GMI characteristics within the whole range of frequency. The domain structure of the above sample has been changed by applying tensile stresses up to 603 MPa and current annealing with a DC current of 50 mA for various time durations, and the corresponding effect on GMI has been studied in detail. A maximum change of 8.85% in MI of the as-quenched sample has been observed around a frequency of 5.05 MHz. Application of an external tensile stress reduces the GMI value by increasing the inner core domain, whereas heat treatment of the sample enhances the same. The square-shaped magnetic hysteresis loop of the as-quenched sample helps us understanding the MI results.     

Transverse anisotropy field and lattice plane anisotropy of stress annealed Fe–Cu–Nb–Si–B ribbons

The transverse magnetic anisotropy and lattice plane anisotropy of stress-annealed Fe–Cu–Nb–Si–B amorphous ribbons have been studied. The GMI effect or impedance ratio decreased gradually with increasing applied tensile stress. The transverse anisotropy field (H_k) corresponded to the full width at half maximum (FWHM) of the GMI curves. A linear response was found between the applied tensile stress (σ) and the transverse anisotropy field (H_k), and it was seen from the linear expression that annealing without stress resulted in a very small H_k of ～200 A/m. We also calculated the strains from the elongations obtained during the stress annealing process, the results showed that the strain and applied stress were linearly related and for a zero-tensile stress, the elastic strain was negative (?0.0219) showing that contraction dominates during annealing without tensile stresses. The lattice plane anisotropy (Δd) calculated from XRD peaks was also linearly related to the applied tensile stress. The lattice spacing in the direction parallel to the tensile stress was elongated while the lattice spacing in the direction perpendicular to the tensile stress was compressed.     

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.     

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.     

电流退火铁基薄带巨磁阻抗效应的影响

研究了电流退火工艺对铁基非晶合金Fe₈₄Zr₈Nb_3.5B_3.5Cu_{1〈/sub>薄带巨磁阻抗效应的影响.实验结果表明,该铁基合金的巨磁阻抗ΔZ/Z随退火电流的增加而增强,当电流为820mA时,ΔZ/Z达到最大值62％,阻抗变化灵敏度可达约0.23％（A/m)^-1.结合此合金在电流退火燧后电性能和软磁性能的演变,讨论了材料的巨磁阻抗效应借助趋肤效应与交流频率和外加纵向磁场的关系. 关键词：}     

Large GMI effect in Co-rich amorphous wire by tensile stress

Quality Co₆₈Fe_4.5Si₁₅B_12.5 amorphous wires are fabricated and their giant magneto impedance (GMI) effect are investigated at frequencies ranging from 0.1 to 20 MHz with or without tensile stress applied. Experimental results indicate that the GMI effect of these wires can be effectively improved by applying a small axial tensile stress. There is a pronounced increase from 1.3% to 47.3% in impedance ratio at 0.6 MHz when a stress of 103 MPa is applied. The GMI response is further increased to 261% by doing so at 15 MHz. The field sensitivity of these wires is optimized and it increases from 0.55 to 2.73%/(A/m) at 0.6 MHz and it is proved that the most sensitive field response is obtained by applying a tensile stress of 84.5 MPa below 1 MHz. With reference to the stress evolution of sensitivity at varying frequencies, the maximum field sensitivity shifts to a lower stress with increasing frequency. Quantitatively, a stress as small as 18.4 MPa is enough to yield a field sensitivity as high as 6.7%/(A/m) at 15 MHz. This demonstrates the possibility of achieving small stress (<100 MPa) induced large enhancement of GMI effect and field sensitivity at frequencies of several tens of MHz that are of much technical interest in sensor applications.     

Influence of glass coating thickness and metallic core diameter on GMI effect of glass-coated Co68Fe4.5Si13.5B14 amorphous microwires

Influences of the size factors (glass coating thickness and metallic core diameter) of microwires on GMI effects of the glass-coated Co₆₈Fe_4.5Si_13.5B₁₄ amorphous microwires were investigated. The results indicated that the GMI effect of the microwires with the same glass coating thickness or the same metallic core diameter was initially increased to a peak and then decreased with an increase in the diameter or the thickness. The glass coating thickness and the metallic core diameter corresponding to the maximum GMI varied with metallic core diameter and glass thickness, respectively. The GMI effect of the microwires with the same geometric size varied remarkably under different cooling rates. Such effect was ascribed to the microstructural changes of the metallic core wire under different cooling rates. The influence of the glass coating thickness on the GMI effect of the microwire was attributed to the synthetical actions of crystallization enthalpy (degree of disorder) and the internal stress.     

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.     

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     

Percolation phenomenon in barium samarium titanate-silver composite

Ba₄Sm_9.33Ti₁₈O₅₄-Ag (BST-Ag) composites were prepared by a solid-state ceramic route and its dielectric properties were investigated in the vicinity of percolation threshold. The structure and microstructure of the composites were analyzed by X-ray diffraction along with optical and scanning electron microscopy observations. The effects of silver content and frequency on the dielectric properties of BST-Ag composites were studied using a LCR meter. The relative permittivity (ε_r) of the composite increases with silver content below the percolation limit and is in agreement with power law. A 0.14 volume fraction of silver loading increases the relative permittivity of the composite from 50 to 450 at 10 kHz. Addition of 0.15 volume fraction of silver increases the relative permittivity of the composite in the order of 10⁵. It is found that the giant relative permittivity is almost constant for frequencies from 1 kHz to 1 MHz. This high ε_r composite offers the perspectives for application in electromechanical devices.     

非晶CoFeNiNbSiB合金的巨磁阻抗效应

研究了非晶Co₇₀Fe_4.5Ni₄Nb₁Si_12.5B₈合金薄带的巨磁阻抗效应.实验表明,在一定频率范围内提高测试频率,磁阻抗效应有明显提高;适当温度的退火也有助于磁阻抗效应的提高.制备态非晶合金样品在频率为5MHz下达120%左右,经过退火处理的非晶样品5MHz下的效应可达400%左右. 关键词：     

TbDyFe薄膜对三明治膜巨磁阻抗效应的影响

将600℃退火后的超磁致伸缩材料(Tb0.27Dy_0.73)_0.3Fe_0.7薄膜作为Ni_80.2Fe_14.1Si_0.2Mn_0.4Mo_5.1三明治膜的基底，制备出四层膜.结果表明：附加的磁致伸缩并没有减小材料的巨磁阻抗(GMI)效应，而由于磁场下磁致伸缩材料的应力效应影响了三明治膜中的各向异性场，使三明治膜的GMI效应增大了4倍.再将制备态的四层膜在280℃下真空退火，退火态四层膜也增大了三明治膜的GMI效应，但可能由于磁致伸缩向磁性层中的扩散，其GMI效应相对于制备态四层膜则有所降低. 关键词： 巨磁阻抗(GMI)效应 三明治膜 TbDyFe薄膜 各向异性场     

Effect of Surface Structure of Nano-CaCO3 Particles on Mechanical and Rheological Properties of PVC Composites

To study the effect of different surface structures on resultant mechanical and rheological properties, nano-CaCO₃ particles were treated with isopropyl tri-stearyl titanate (H928), isopropyl tri-(dodecylbenz-enesulfonyl) titanate (JN198), and isopropyl tri-(dioctylpyrophosphato) titanate (JN114). Scanning electron microscopy (SEM) and dynamic mechanic analysis (DMA), carried out to characterize the effective interfacial interaction between the nano-CaCO₃ particles and a poly(vinyl chloride) (PVC) matrix, indicated that JN114 treated nano-CaCO₃ particles had the strongest interfacial interaction with a PVC matrix, while H928 treated nano-CaCO₃ had the weakest. The rheological and mechanical properties of PVC/nano-CaCO₃ composites were investigated as a function of surface structure and filler volume fraction. The tensile yield stress and elongation at break decreased with the increasing of calcium carbonate content while tensile modulus increased. PVC filled with JN114 treated nano-CaCO₃ had the highest tensile modulus and tensile yield stress, while those filled with H928 treated nano-CaCO₃ had the highest elongation at break at the same filler content. The impact strength of PVC/nano-CaCO₃ composites increased with the increasing of CaCO₃ content, and PVC composites filled with JN198 treated nano-CaCO₃ particle had a higher impact strength than those with JN114 or H928 treated, with the value reaching 23.9 ± 0.7 kJ/m² at 11 vol% CaCO₃, four times as high as that of pure PVC. Rheological properties indicated that a suitable interfacial interaction and a good dispersion of inorganic filler in a PVC matrix could reduce the viscosity of PVC/nano-CaCO₃ composites. The interfacial interaction was quantitatively characterized by semiempirical parameters calculated from the tensile strength of PVC/nano-CaCO₃ composites to confirm the results from the SEM and DMA experiments.     

Giant magneto-impedance effect in CoMnSiB amorphous microwires

The giant magneto-impedance (GMI) ratio, ΔZ/Z=[(Z(H)−Z(H_max)]/Z(H_max), in a nearly zero magnetostrictive Co_68.5Mn_6.5Si₁₀B₁₅ amorphous microwire has been investigated for the frequency range 0.5–10 MHz, driving current amplitude of 0.5–2.5 mA, bias DC magnetic field up to 2400 A/m and under applied tensile stress up to 132 MPa. A maximum relative change in the GMI ratio up to around 130% is observed at a frequency of 10 MHz, magnetic DC field of about 180 A/m, driving current amplitude of 1 mA and under tension of 60 MPa. The tensile stress dependence of the magnetic field, H_m, corresponding to the maximum ΔZ/Z ratio allows to estimate the magnetostriction constant (λ_s≈−2×10⁻⁷) to be in good agreement with λ_s values estimated by different methods and in amorphous alloys with similar compositions.     

Interface effect in the silicone rubber/mineral powder composites

Silicone rubber/mineral powder composites have been prepared by surface modification and ultrafinecrashing of mineral powder, mixing and vulcanizing with silicone rubber resin. The surface and interface energy for mineral filler and silicone rubber matrix were investigated. It was found that there is a correlation between W _a/σ_SL (interfacial adhesive work/interfacial tension) and the tensile strength of the corresponding composite, especially for unmodified ultrafine mineral filler. On the other hand, the chemical modification of the surface changes the surface group on the mineral filler and results in improvement of the interfacial interaction between silicone rubber matrix and mineral filler, consequently, altering the reinforcing effect of the mineral filler.     

Evolution of magnetic permeability and magneto-impedance effect in composite wires with insulator layer

CuBe/Insulator/NiCoP composite wire was prepared by electroless deposition on an insulated CuBe core with a diameter of 90 μm. The conversion relationship between the magneto-impedance and effective magnetic permeability of the composite wire was derived from an energy conversion model. The evolution of the magnetic permeability and the giant magneto-impedance (GMI) effect were investigated. The results show that a distinct GMI effect can be obtained at relatively low frequency. The largest GMI ratio is 240% at 600 kHz, and the maximal field sensitivity is 34%/Oe.     

Low-density core-shell composite hollow microspheres with tunable magnetic properties

Low-density (about 0.9 g/cm³) composite core-shell hollow microspheres with tunable magnetic properties were fabricated by Ni-Fe-P deposition on hollow glass microspheres (HGM) with modified electroless plating process. The effects of mole ratio of Fe²⁺/Ni²⁺, concentration of the reducer and pH value of the solution on the magnetic properties of the products were investigated. In conclusion, the increase in the mole ratio of Fe²⁺/Ni²⁺ and pH value of the solution could improve the soft magnetic properties of composite microspheres remarkably, while the increase in the concentration of NaH₂PO₂ had the opposite effect. The as-obtained metallic shells were amorphous and the crystallization got better with increased annealing temperature after plating. In addition, the saturation intensity of the composite microspheres was enhanced monotonically by increasing the annealing temperature. This work provided a facile and effective strategy to fabricate core-shell composite hollow microspheres with tailored magnetic properties.     

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.     

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.     

Influence of Ge on magnetic and structural properties of Joule-heated Co-based ribbons: Giant magnetoimpedance response

Studies of magnetic and structural properties of Fe_3.5Co_66.5Si_12−xGe_xB₁₈ (x=0, 3, and 6) soft magnetic ribbons obtained by melt-spinning were performed. The samples were submitted to Joule-heating treatments with different maximum current values (0.01, 0.05, 0.1, 0.2, and 0.8 A, respectively) with steps of 0.01 A and times by step of 1, 2, and 10 s). X-ray diffraction, temperature dependence of magnetization (for the as-quenched samples), coercivity and giant magnetoimpedance (GMI), measured at different frequencies (100, 500, and 900 kHz, respectively) were performed. All the samples crystallized at annealing currents higher than 0.4 A, which was consistent with the magnetic hardening of the material. Coercivities less than 1 A/m were obtained for the three samples between 0.1 and 0.2 A. Maximum value of GMI response was observed for the sample without Ge in the as-quenched state.