Giant Magnetoimpedance Properties Research Articles

Enhanced Giant Magnetoimpedance Properties of Fe-Based Amorphous Ribbons by Coating Soft Magnetic Film

Enhanced Giant Magnetoimpedance Properties of Fe-Based Amorphous Ribbons by Coating Soft Magnetic Film

Surface microstructural design to improve mechanical and giant magneto-impedance properties of melt-extracted CoFe-based amorphous wires

The influence of surface microstructural regulation mechanisms on the mechanical and giant magneto-impedance (GMI) properties of as-cast melt-extracted CoFe-based wires has been systematically researched based on morphology, phase distribution and domain structure parameters. A series of statistical models were applied to analyze the mechanical properties and followed by mapping the curve of cumulative failure rate for wire application. It was found that the average and highest fracture strengths, average tensile strain increased with Cu substitution and reached peaks of ~3725 MPa, ~4250 MPa and ~2.7%, respectively. Verified structure-simulation experiments revealed that surface Rayleigh waves effectively split the main crack and the diffusely distributed nanocrystalline in surface area acted as a pinning point to impede the crack growth, enhancing the mechanical properties. The GMI ratio displayed similar variations and attained a maximum value of 700 ± 5% as well as the resistance and reactance ratios improved to ~687% and ~2206%, respectively. The enhanced relative dielectric permeability μs resulting from the increased domain wall energy density and the decreased surface domain width. The unique synchronous enhancement of CoFe-based wires satisfies the demand for emerging magnetoelectric sensor applications, e.g. flexible and wearable sensors, equipment self-monitoring sensors, and array robotic skin sensors under harsh working environments.

Oil-medium current annealing enhanced giant magneto-impedance properties of Co-based metallic microfibers for magnetic sensor applications

Herein, the effect of oil-medium current annealing on GMI characteristics of rotated-dipping Co-based metallic microfibers was investigated systematically. Based on thermophysical parameters of the metallic microfibers (containing glass transition temperature Tg and initial crystallization temperature Tx1), we constructed a steady-state heat conduction model by ANSYS to simulate the temperature field distribution during its oil-medium current annealing process, and further to determine the annealing current intensity range: 50 mA˜300 mA, according to the crystallization degree of cores of microfibers. The experimental results indicated that, in comparison to as-cast Co-based microfibers, the maximum GMI ratio [ΔZ/Zmax]max and the maximum magnetic field response sensitivity ξmax of oil-medium current annealed microfibers were both significantly improved. Among which, [ΔZ/Zmax]max and ξmax of the microfibers annealed at 225 mA can reach 303.1% and 50.6%/Oe, respectively, at the excitation current frequency f =5 MHz, and the maximum response field Hp increased from 1 Oe to 3 Oe. Meanwhile, the magnetic domain arrangement of oil-medium current annealed microfibers became denser, the width of which got smaller, and the transition regions of domain changed into clearer. This improvement of GMI characteristics is closely related to magnetic domain distribution regulated by high-intensity toroidal magnetic field, which was generated during the medium current annealing process. That is, the atomic magnetic moment tends to be closely and orderly adjusted by the combined action of both the magnetic field energy and thermal activation energy.

Cycle rapid cooling treatment effect on the magnetic properties and giant magnetoimpedance properties of Co-based amorphous alloy ribbons

The influence of cycle rapid cooling treatment on the giant magnetoimpedance (GMI) properties in Co-based amorphous alloys was investigated. Hysteresis loops show that the saturation magnetization of ribbons has been improved by cycle treatment. It can be found that the GMI ratio was increased from 89% to 130% at 1MHz by the thermal cycle (TC) treatment. Moreover, GMI ratio of TC treatment sample increased up to 321% at 5MHz. It is considered that internal thermoelastic stress leads to surface roughness, magnetic domain structures and saturation magnetization changes of the ribbons during different cycle processes. It was also found that the asymmetric GMI (AGMI) phenomenon occurred in the Co-based alloys with TC treatment after annealing, which can be regarded as a new method to get GMI-valve to improve GMI sensitivity.

Investigating magnetic properties of Co68Fe4B15Si13 amorphous alloy by molecular dynamics and DFT calculations

Cobalt-based amorphous alloys, in particular CoFeBSi, have been widely used to study the response of ac-impedance to the external dc magnetic field, i.e., the so-called Giant Magneto Impedance (GMI) effect. The utility of CoFeBSi in different applications such as field-sensitive sensors is known and practiced. Despite the wealth of experimental studies on GMI properties of CoFeBSi alloys, no computational approach has yet been addressed on electronic and magnetic properties of these systems at nanoscales. In this study, we have computed electronic and magnetic properties of amorphous CoFeBSi alloys using a combined Molecular Dynamics (MD) and Density Functional Theory (DFT) approach. MD is used to provide a physically realistic sampling of different atomic configurations while the properties such as dipole moments and magnetic susceptibilities are computed using DFT. Our study shows a wide spectrum of electronic as well as magnetic properties for nanoclusters of different sizes having implications for rational design of Co-based ferromagnetic alloys.

Magnetoimpedance Effect in CoFeMoSiB As-Quenched and Surface Modified Amorphous Ribbons in the Presence of Igon Oxide Nanoparticles of Water-Based Ferrofluid

Giant magnetoimpedance (GMI) has been proposed as a powerful technique for biosensing. In GMI biosensors based on the magnetic label detection the change of the impedance of sensitive element under the application of an external magnetic field was analyzed in the presence of magnetic nanoparticles in a test solution. Amorphous ribbon-based GMI biodetectors have an advantage of low operation frequency and low cost. In this work, magnetic and GMI properties of amorphous Co68.6Fe3.9Mo3.0Si12.0B12.5 ribbons were studied in as-quenched and surface modified states both without and in the presence of maghemite ferrofluid. After the surface modification the coercivity was slightly increased and saturation magnetization decreased in good agreement with increase of the surface roughness, a decrease of magnetic elements concentrations in the surface layer, and formation of a surface protective oxide layer. The GMI difference for as-quenched ribbons in absence and in the presence of ferrofluid was measurable for the frequency range of 2 to 10 MHz and the current intensities of 1 to 20 mA. Although the proposed surface modification by the ultrasound treatment did not improve the sensitivity limit for ferrofluid detection, it did not decrease it either.

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

In this work, the impedance properties of Co68.15Fe4.35Si12.5B15 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.

Multiplex magnetic field annealing evoked remarkable GMI improvement in co-based amorphous wires

We have proposed a series of novel tailoring techniques for integrating conventional vacuum annealing (CVA) and the specific (e.g. transverse- and rotated-) magnetic field annealing (as denoted by TMFA and RMFA respectively), and systematically investigated the impacts of them on the giant magnetoimpedance (GMI) properties and domain microstructure of Co-based amorphous wires. Experimental results indicated that a multiplex MFA treatment i.e, two-step CVA annealing under a rotated magnetic field of 4000Oe, can realize remarkable enhancement of GMI in comparison with the as-prepared, CVA-treated and MFA-treated wires. The GMI ratio increased firstly and then tended to be stable with increasing frequency, moreover, both permeability and GMI ratio decreased with the increase of DC magnetic field. At 13 MHz, the maximum GMI ratio [ΔZ/Zmax]max and field response sensitivity ξmax of RMFA-ed wires increased to 398.39% and 21.84%/Oe, respectively, which is 2.41 times and 3.17 times than those of 165.18% and 6.88%/Oe for the as-prepared wires. Essentially, the physical process of RMFA action is mainly described as the multi-angle induced magnetic anisotropy and atomic reordering dynamic process due to the co-action of rotatory variation magnetic field energy and thermal activation. Meanwhile, the GMI behavior of TMFA evolving from single peak (SP) to double peaks (DPs) is attributed to the increase of magnetic domain driving force (namely domain wall movement increment) and uni-directional inducing magnetic anisotropy at relatively high frequency, which modified the GMI ratio and field sensitivity to 334.61% and 33.51%/Oe, respectively. Therefore, it can be concluded that both RMFA & TMFA would be used to explore microwires with enhanced GMI property for high-performance sensor applications.

The Influence of Series and Parallel Current Flowing Through Two Paralleled Co-based Amorphous Wires on Giant Magneto Impedance Effect

Background: Giant Magneto Impedance (GMI) is effectively enhanced by the mutual magnetic interaction between two wires arranged in parallel setup. The direction of current flowing through two wires (series or parallel current mode) has a key role in this change. Methods: The aim of this research is to study the GMI properties of series and parallel current flowing through two amorphous Co-based wires in parallel setup and compare it to a single wire. Therefore, the wires with stoichiometric formula Co 68.15 Fe 4.35 Si 12.5 B 15 were prepared by in-rotating water spinning method with diameter about 125 μm. Findings: The best GMI response measured in series current mode and 8 mm distance between two wires. The GMI ratio increases from 300% of single wire to 480% of two wires in series current mode. However when the current flowing through two wires is in parallel mode, the GMI ratio decreases to 180% which is due to reduction of effective magnetic field. For two-wire system in series current mode, the magnetic interaction is stronger than parallel current configuration. Application: These results demonstrate that the GMI response could be effectively improved in two-wire series current system, which is useful for the application of low dimension and high sensitive GMI sensors.

Anisotropic Mechanical and Giant Magneto-Impedance Properties of Cobalt-Rich Amorphous Ribbons

A comparative study was performed on the mechanical and giant magneto-impedance (GMI) properties in the longitudinal and transverse directions of Co69Fe4Ni1Mo2B12Si12 amorphous ribbons. Both mechanical and GMI properties were found to be anisotropic. Kerr microscopy shows the presence of a stripe-type domain structure with the magnetic easy axis parallel to the longitudinal direction. The fracture strength, elastic modulus, and fracture toughness in the transverse direction was higher than those in the longitudinal direction. A larger GMI response was achieved in the transverse direction at a frequency range where both the domain wall motion and spin rotation dominantly contributed to the effective permeability and hence the magneto-impedance. The current study paves the way for designing Co-rich amorphous ribbons as desirable components in electronics such as magnetic sensors.

The effect of current frequency and magnetic field direction in alternative current-field annealing on the GMI and magnetic properties of Co-based wires

The effects of applied current annealing frequency, amplitude and magnetic field direction during alternative current-field annealing on giant magnetoimpedance (GMI) and magnetic properties of Co68.15Fe4.35B12.5Si15 wire have been investigated. This annealing process leads to a complex domain structure because of the existence of the variable internal circumferential field and external static magnetic field. We have demonstrated that the applied current annealing with different frequencies, amplitudes and magnetic field directions can improve the magnetic properties and the GMI response. In the as-quenched wire, GMImax and saturation magnetization (Ms) are equal to 220% and 78.5 emu/g respectively. They grow up to 400% and 87.2 emu/g, respectively, while the amplitude of the 50 Hz annealing current is 400 mA and the applied magnetic field, perpendicular to the wire, cancels out the earth's magnetic field. In contrast, the samples annealed by 50 Hz (500 mA) and 100 kHz (400 mA) alternative currents show GMImax = 50% and 140%, and also Ms = 41.8 and 40.7 emu/g, respectively. Altogether, our results show that alternative current-field annealing at appropriate conditions improves the GMI response and makes the samples more suitable for magnetic sensing.

Giant magnetoimpedance effect and domain wall dynamics in Co-rich amorphous microwires

The giant magnetoimpedance (GMI) effect, as well as the magnetic and magneto-optical properties, of Co69.2Fe4.1B11.8Si13.8C1.1 and Fe73.8Cu1Nb3.1B9.1Si13 amorphous microwires is studied. It is observed that the magnetic properties and the GMI effect of the Co-rich microwire can be tuned by heat treatment. A high GMI effect has been observed in as-prepared Co-rich microwires. After appropriate annealing of the Co-rich microwires, fast domain wall propagation and a GMI effect can be simultaneously observed in the same sample, and annealing is seen to affect both the diagonal and off-diagonal GMI components. Using complementary studies of the bulk and surface magnetic properties, an attempt is made to explain the great difference observed in the GMI properties of Co- and Fe-based microwires exhibiting very similar bulk hysteresis loops.

Parametric controls on giant magnetoimpedance (GMI) behaviour of CoFeSiBCr amorphous wires for prospective sensor applications

Investigation is focused on the effect of different parametric controls like driving frequency, amplitude of the alternating current (ac), direct current (dc) bias field and anisotropy field (Hk) on the Giant Magneto-Impedance (GMI) properties of rapidly quenched soft magnetic Co66Fe2Si13B15Cr4 amorphous wires developed by in-water quenching technique. Optimal controls of these parameters like driving frequency and amplitude of the ac were found to display a sensitive change in GMI properties at optimal frequency of 5MHz and 5mA driving current. The influence of these controls on the output factors like maximum GMI ratio (GMImax), transition from single peak (SP) to double peak (DP), field sensitivity of GMI (η) and anisotropy field (Hk) throw light on the application of the developed wires for sensors. In addition to high Hk, driving frequency of 5MHz also delivered a combination of desirable sensor properties like high level of sensitivity and its enhanced span of stability. Joule heating further improved the GMI response of the material through current annealing at a current density of 5A/mm2.

Optimization of mechanical and giant magneto‐impedance (GMI) properties of melt‐extracted Co‐rich amorphous microwires

In this work, we report a comprehensive investigation on mechanical and giant magneto‐impedance (GMI) properties of melt‐extracted Co‐rich amorphous microwires with the nominal composition of Co69.25Fe4.25Si13B13.5−xNbx (x = 0, 1, 2, 3, 4). Results show that the tensile strength and GMI properties gradually increase with the substitution of B by Nb at first, and then decrease with a further Nb substitution. The melt‐extracted microwires with the substitution of B by 3% Nb exhibit a maximum tensile strength σm of 4000 ± 50 MPa owing to the formation of nanosized crystals in the amorphous matrix. In addition, the substitution of B by 1% Nb assures an excellent GMI property. At 5 MHz, the maximum GMI ratio [ΔZ/Zmax]max for the melt‐extracted microwires reaches as high as 450 ± 10% versus 380 ± 10% for traditional CoFeSiB microwires and the field‐response sensitivity increases from 350 ± 10% Oe−1 to 700 ± 10% Oe−1 for 1% Nb substitution. It is thus concluded that both mechanical and GMI properties of the melt‐extracted Co‐based amorphous microwires can be greatly improved by properly adding Nb, and this is promising for many engineering applications, including high‐resolution magnetic, stress and biomedical sensors.

Optimization of GMI properties by AC Joule annealing in melt‐extracted Co‐rich amorphous wires for sensor applications

We report here on a comprehensive study of an alternating‐current Joule annealing (ACJA) method for optimizing the giant magnetoimpedance (GMI) effect of Co‐rich amorphous wires for sensor applications. Experimental results indicated that the proper ACJA treatment can drastically improve the GMI property of as‐cast wire. At 10 MHz, the maximum GMI ratio [ΔZ/Z0]max of ACJA‐ed wire increase to 205.38%, which is nearly 3.3 times that of 62.84% for as‐cast wire, and the maxima field response sensitivity ξmax of ACJA‐ed wire increases to 345.90%/Oe by more than twice that of 170.92%/Oe for as‐cast wire. With an increase of AC amplitude, a remarkable dependence of GMI performance appears on the microstructural evolution such as the structural relaxation, the degree of local order, as well as circular magnetic domains. Importantly, the atomic order orientation incorporating HRTEM observation and circumferential permeability were effectively increased by the co‐action of thermal activation energy and magnetic field energy during ACJA, further to enhance the magnetic properties to some extent. Based on both the numerical calculation of transient temperature rise and GMI behavior, we propose ACJA as an efficient annealing technique to achieve simultaneous best performance of [ΔZ/Z0]max and ξmax for potentially magnetic sensor applications in detecting weak magnetic fields.

Giant magneto-impedance effect of two paralleled amorphous microwires

Giant magneto-impedance (GMI) is effectively enhanced by the mutual magnetic interaction between two amorphous microwires. A comparative study on GMI properties of a single wire and two wires arranged in parallel mode was reported in this work. Two-peak (TP) of impedance characteristic is presented when the dc external field changed from 0 to 320 A·m−1 in two-wire system, which is attributed to successive magnetization process in two wires induced by their magnetic interaction. And the evolution of single peak to TP phenomenon, when the distance between two wires is upto 8 mm, evidences a distance dependence of transformation from successive magnetization to simultaneous via a corresponding distance dependence of magnetostatic interactions. It is proposed that the recombination of magnetic interaction and the shielding effect results in a distance dependency of GMI response. When the distance is 8 mm, the magnetization process is close to synchronous between two wires, which give rises to higher circular permeability and better GMI response. The impedance ratio ΔZ/Z increases from 74.5 % of single wire to 172.4 % at 10 MHz. However, when the distance is upto 12 mm, the magnetic interaction is weak and magnetization process is completely independent, and GMI response decreases, relatively. This indicates that the GMI response could be effectively improved in a two-wire connection with an optical distance, which is promising and useful for the application of high-performance GMI sensors.

Optimization of process parameters for developing FeCoSiB amorphous microwires through in-rotating-water quenching technique

The effects of process parameters for the in-rotating-water quenching technique have been investigated with respect to structural, magnetic and giant magneto-impedance (GMI) properties of FeCoSiB alloy microwires. Continuous and ductile amorphous wires have been found with the optimization of process parameters. The structural, magnetic and GMI behaviors have been evaluated as a function of wire diameter. The crystallinity of the wires increases with wire diameter, affecting soft magnetic and GMI properties. Consequently, it is found that the wire of 110 μm diameter shows superior soft magnetic and GMI properties.

Relating residual stress and microstructure to mechanical and giant magneto-impedance properties in cold-drawn Co-based amorphous microwires

The effect of cold-drawing on the tensile property and giant magneto-impedance (GMI) effect of melt-extracted Co-based amorphous microwires was evaluated through detailed analyses of the distribution of residual stress and microstructural evolution. The tensile ductility and tensile strength increased gradually with cross-sectional area reduction ratio (R) until 51%, and decreased with further deformation. The microwire with R=51% exhibits the highest tensile ductility of 1.09% and tensile strength of 4320MPa. Structural and thermodynamic analyses reveal that it is the mechanical deformation rather than thermal activation that induces the precipitation of nanocrystals and arrests the quick extension of shear bands leading to the enhanced ductility. Interestingly, the GMI effect also attains the maximum value of 160% at 10MHz when R=51% (30% larger than that of the as-cast wires), before decreasing with further cold-drawing. Such an identical evolution trend of both tensile and GMI properties can be ascribed to two underlying mechanisms: the generation of longitudinal and circumferential residual stresses and the growth of deformation-induced nanocrystals during cold-drawing. The role of residual stress is established herein not only as a trigger to accelerate the amorphous-to-nanocrystalline phase transformation but also as a decisive contributor to the mechanical and GMI performance. The unique simultaneous improvement of both mechanical and GMI properties of cold-drawn Co-based microwires opens up new possibilities for a variety of engineering applications, such as high-performance magnetic, stress and biological sensors.

Effect of Nb and Cr incorporation on the structural and magnetic properties of rapidly quenched FeCoSiB microwires

Rapidly quenched microwires with a nominal composition of Fe39Co39Si8B14 (#AO), Fe37Co37Nb4Si8B14 (#AN) and Fe36Co36Nb4Cr2Si8B14 (#ANC) have been investigated. Devitrification of as-quenched microwires showed that crystallization temperatures increased with simultaneous incorporation of Nb and Cr as in #ANC alloy. Addition of these elements also contributed to an increase in activation energy in #AN and #ANC alloys. Nb addition reduced the particle size, which became much finer in the case of the Cr-containing alloy. Although Nb addition did not have much effect on lowering the Curie temperature TC of the amorphous phase, Cr substitution lowered TC to 698K from high values of 785K and 787K observed in the #AO and #ANC alloys, respectively. However, the Cr addition revealed a better Giant magneto-impedance (GMI) response compared to the other alloys. Such improved GMI properties in the Cr-containing alloy are attributed to lower values of the coercivity and magnetostriction in the alloy containing both Nb and Cr.

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 (Co0.5Fe0.5)78−xCrxSi8B14 (x=0–12) amorphous microwires of 110μm diameter prepared by in-water quenching technique. The rise in crystallization onset TX1 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 Tca with its rise in concentration. The presence of low Cr content upto Cr-4at.% 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.