Giant Magnetoimpedance Ratio Research Articles

GMI-based biosensor for the detection and quantification of doxorubicin anticancer drugs labeled to Fe3O4 superparamagnetic nanoparticles

We present the results of research on a Co-based giant magnetoimpedance (GMI) biosensor for Fe3O4-labelled doxorubicin (DOX) anticancer drugs. Co62Fe5Ni4Si15B14 ribbons were used as biosensing material for test solutions containing different concentrations of DOX. The plain ribbon, ribbon+Fe3O4 and ribbon+DOX2 samples exhibited low coercivity (Hc), high saturation magnetization (Ms) and low anisotropy (Hk). The GMI ratio (ΔZ/Z) increased from 33% to 38% with the increase of doxorubicin content in the ribbon. It was found that the ΔZ/Z ratio first increased rapidly up to a frequency of ∼2 MHz, and then decreased slowly as the frequency increased. While the magnetic field dependent ΔZ/Z has a single peak at 1 MHz, it has a double peak at 5 MHz. It was found that the peak height of ΔZ/Z in the ribbons with test solution of 20 ng/ml and 50 ng/ml increased by ∼3% and ∼6%, respectively, compared to the ribbon without test solution. Then the ΔZ/Z ratio decreased very rapidly with the increase of the applied external magnetic fields. The frequency-dependent GMI sensitivity (η) increased with increasing frequency and reached a maximum value at a critical frequency (∼1.6 MHz), after which it decreased. The detection sensitivity of the GMI biosensor (ξ) increased rapidly with increasing doxorubicin concentration up to ∼80 ng/ml and then remained almost unchanged. The results show that doxorubicin (DOX+Fe3O4), used as an anticancer drug, can be effectively detected even at low concentrations using the GMI based sensors fabricated in this study.

Line spacing effect on the giant magnetoimpedance behavior on microribbon with meander type: a comparison of theory and experiment

Purpose Microribbon with meander type based on giant magnetoimpedance (GMI) effect has become a research hot spot due to their higher sensitivity and spatial resolution. The purpose of this paper is to further optimize the line spacing to improve the performance of meanders for sensor application. Design/methodology/approach The model of GMI effect of microribbon with meander type is established. The effect of line spacing (Ls) on GMI behavior in meanders is analyzed systematically. Findings Comparison of theory and experiment indicates that decreasing the line spacing increases the negative mutual inductance and a consequent increase in the GMI effect. The maximum value of the GMI ratio increases from 69% to 91.8% (simulation results) and 16.9% to 51.4% (experimental results) when the line spacing is reduced from 400 to 50 µm. The contribution of line spacing versus line width to the GMI ratio of microribbon with meander type was contrasted. This behavior of the GMI ratio is dominated by the overall negative contribution of the mutual inductance. Originality/value This paper explores the effect of line spacing on the GMI ratio of meander type by comparing the simulation results with the experimental results. The superior line spacing is found in the identical sensing area. The findings will contribute to the design of high-performance micropatterned ribbon with meander-type GMI sensors and the establishment of a ribbon-based magnetic-sensitive biosensing system.

Optimization of Giant Magnetoimpedance Effect of Amorphous Microwires by Postprocessing

Magnetic microwires with amorphous structures can present a unique combination of excellent magnetic softness and giant magnetoimpedance (GMI) effects together with reduced dimensions and good mechanical properties. Such unique properties make them suitable for various technological applications. The high GMI effect, observed in as-prepared Co-rich microwires, can be further optimized by postprocessing. However, unexpected magnetic hardening and a transformation of the linear hysteresis loop into a rectangular loop with a coercivity on the order of 90 A/m were observed in several Co-rich microwires upon conventional annealing. Several routes to improve magnetic softness and GMI effect in Fe- and Co-rich magnetic microwires are provided. We observed that stress annealing could remarkably improve the magnetic softness and GMI ratio of Co-rich microwires. Thus, almost unhysteretic loops with a coercivity of 2 A/m and a magnetic anisotropy field of about 70 A/m are achieved in Co-rich microwires stress annealed at appropriate conditions. The observed change in hysteresis loops and the GMI effect is explained by stress-annealing-induced anisotropy, which is affected by the stresses applied during annealing and by the annealing temperature. While as-prepared Fe-rich amorphous microwires present a low GMI effect, appropriate postprocessing (annealing and stress annealing) allows for a remarkable GMI ratio improvement (an order of magnitude). The evaluated dependence of the maximum GMI ratio on frequency allows the identification of the optimal frequency band for the studied samples. The origin of stress-annealing-induced anisotropy and related changes in hysteresis loops and the GMI effect are discussed in terms of the relaxation of internal stresses, “back-stresses”, as well as structural anisotropy.

Impact of stress and magnetic field in annealing process on GMI and GSI effect of CoFeSiB amorphous material

This study focuses on investigating the impact of various annealing methods on the giant magneto-impedance (GMI) and giant stress induced GMI (GSI) effects of Co68Fe4.5Si12.5B15 ribbons. The GMI and GSI effect of the ribbons were characterized by impedance ratio under different annealing methods. The results indicate that the ribbon annealed with appropriate current density and additive 100 MPa tensile stress in Joule annealing exhibits the significant GMI ratio enhancing by 19.43 %. The study also demonstrates the significant influence of magnetic field in annealing, with magnetic field annealing showing great potential to improve both the GMI and GSI effects, increasing them to 75.76 % and 25.8 %, respectively. These findings provide insights into the development of materials with high sensitivity and thermal stability for modern sophisticated sensors.

Optimization of temperature stability and sensitivity of the giant magnetoimpedance effect in meander shaped Co-based amorphous ribbon using DC-biased current for sensor application

The influence of DC-biased current (I DC) on the longitudinal giant magnetoimpedance (GMI) effect in Co-based amorphous ribbon with a meander structure, taken from room temperature to 120 °C, has been investigated. The results show that I DC increases the temperature stability of the impedance of amorphous ribbon at 20 MHz. By deriving the expression of the transverse permeability according to a magnetization rotation model, we attributed the improved temperature stability to the combined effect of temperature and bias field H DC generated by I DC on the transverse permeability. It is also shown that I DC not only effectively inhibits the weakening of the GMI ratio at high temperature, but also significantly improves the GMI sensitivity. This will help to achieve sensitive low magnetic field measurement under large temperature fluctuation.

Optimizing the magnetic and giant magneto-impedance (GMI) properties of glass-coated amorphous Co-based wires via single- and two-step direct current annealing

The effects of both single- and two-step direct current (DC) annealing procedures on the magnetic properties (including the giant magneto-impedance (GMI)) of glass-coated Co66Fe6Si13B15 amorphous wires were evaluated. For both methods, the GMI ratio initially increased with the current intensity and reached a peak value before declining at higher current intensities. A maximum improvement of the GMI ratio of about five times was obtained for the two-step DC-annealed sample, while that for single-step DC-annealed samples was only 2.44 times. A higher GMI sensitivity was also observed for the two-step DC-annealed wires. The better GMI performance of the two-step DC annealed samples was attributed to the more homogeneously distributed precipitation in the matrix and the ordered circumferential magnetic domains on the surface. The results obtained further imply that DC annealing at a higher current intensity but over a shorter treatment time is a more efficient and energy-saving method for enhancing the GMI performance of Co-based amorphous wires for potential industrial applications.

Tuning rotational magnetization for high frequency magnetoimpedance in micro-patterned triangle spiral magnetic systems

Achieving high sensitivity, resolution, and accuracy is desirable and in high demand for magnetic sensor applications. The giant magnetoimpedance (GMI) effect has drawn intensive attention owing to its ultrasensitive response to the magnetic field. Further enhancement of the GMI effect in soft magnetic conductors (wires, ribbons, or films) is essential but represents a big challenge since the experimentally reported highest GMI ratio is still much smaller than its theoretically predicted value. Inspired by the kirigami structures, we propose a new approach for improving the GMI effect by designing triangle spiral magnetic systems. We demonstrate that the GMI ratio can be easily tuned by varying the edge width of the triangle spiral magnetic ribbon. The GMI ratio is enhanced up to 250% and 100% for the Fe 92.5 C 3.5 Si 3.9 ribbon with a 60 μm wide edge when a magnetic field of 100 Oe is aligned along the altitude and edge directions, respectively. Magnetometry indicates that upon reduction of the edge width, the improvement of magnetic susceptibility at low applied fields is correlated with the strengthened shape anisotropy. Micromagnetic simulations suggest that various closure magnetic domain configurations such as stripe and zig-zag domain structures can be formed, depending on the applied magnetic field directions, as a result of the competition of anisotropy and Zeeman energies followed in the Stoner-Wohlfarth model. The simulated results fully support the experimentally observed GMI enhancement and attribute it to the formation of transverse magnetic domains at the critical dimension of the micro-patterned magnetic ribbon system. These superior properties make the triangle-spiral GMI sensor a promising candidate for advanced sensor applications. • Various branch-width triangle spiral magnetic systems have been developed and characterized, at which optimized 60 μm width showing the best GMI effect owing to the strengthened shape anisotropy. • The GMI effect is augmented up to 250% and 100% under an applied magnetic field of 100 Oe aligned along with the altitude and edge directions, respectively. • The GMI enhancement is supported by transverse domain formations approved by OOMMF micromagnetic simulation. • Wide range of magnetic domain configurations can be formed depending on the applied magnetic field directions, originating from the competition of anisotropy and Zeeman energies followed in the Stoner-Wohlfarth model.

Large Linear Giant Magneto-Impedance Response of Microwire Annealed under Liquid Medium for Potential Sensor Applications

Herein, we have presented the giant magneto-impedance (GMI) effect, microstructure and surface domain structure of the Co-Fe-based amorphous microwires after liquid medium—anhydrous ethanol Joule annealing (AJA). The AJA technique can effectively release the radial stress and induce large a circumferential magnetic field by changing the Joule heat transfer and the circumferential domain, to further tune the GMI performance of microwire. The linear response fields (0~3.5 Oe), the high sensitivity of 124.1%/Oe and the high GMI ratio make the microwire as promising materials for the miniaturized GMI sensors. The GMI ratios of [ΔZ/Z0]max(%) and [ΔZ/Zmax]max(%) increase the near-linearly to 201.9% and 200.5%, respectively, for the 250 mA anhydrous ethanol Joule annealed wires. Moreover, a linear response to Hex (ranging from 3.5 to 25 Oe, or more) is observed, which bears the potential in fabricating bi-sensors.

Influences of Anisotropic Equivalent Field and Magnetic Damping Coefficient on Giant Magnetoimpedance Effect of Cylindrical Alloy Fibers: Theoretical Magnetoimpedance Calculations

In this paper, the giant magneto-impedance (GMI) model of a cylindrical alloy fiber was established by the Maxwell equation and Landau–Lifshitz equation to simulate the influence of physical parameters of cylindrical alloy fiber on GMI under different control parameters. MATLAB was employed to calculate the magneto-impedance of cylindrical fibers and draw its curves. We found that when the anisotropic equivalent field of the fiber changes from 10Oe to 50Oe, the peak position of the GMI ratio also moves from about 10Oe to 50Oe, and the peak value gradually increases from 100% to 300%. The GMI ratio increased rapidly with the decrease in the magnetization damping coefficient. Our findings could further guide the design of supersensitive micro GMI sensors by optimally regulating the magnetic damping coefficient, the angle between the external magnetic field and easy axis and the anisotropic equivalent field of cylindrical alloy fibers.

Giant magneto-impedance effect adjusted by electrolytic polishing and thinning of Co-based amorphous ribbons

The giant magneto-impedance (GMI) effect of Co-based ribbons treated by using electrochemical polishing method has been investigated. The initial susceptibility (χi ) and the longitudinal GMI ratio (L-GMI) as a function of the polishing time (t poli) were measured and discussed. The L-GMI firstly increases and then decreases with the increasing of t poli. At t poli = 30 s, the maximum GMI of ∼270% is obtained. This L-GMI trend as a function of t poli is mainly attributed to the variation of effective magnetic anisotropy (H k,eff). The variation of H k,eff comes from the optimization of surface qualities as well as the thinning of the thickness. The thinning of the Co-based ribbons results in the changing of demagnetization effect and, more importantly, the variation in the residual stress distributions. The latter effect will strongly affect the magnetization conditions for the samples with longer t poli: stress variation here is dominant over the influence of surface qualities in the final GMI effect. Furthermore, another factor that may influence GMI is the current density variation related to thickness decrease. At the same time, reducing of stray fields, closely related to surface qualities, is the dominant factor affecting GMI for the samples with shorter t poli.

Stress-induced giant magneto-impedance effect of amorphous CoFeNiSiPB ribbon with magnetic field annealing

The development of high-performance magnetic field-sensitive materials is in urgent need for magnetic sensors. In this paper, the effect of magnetic field annealing on the soft magnetic properties, thermal stability and stress-induced giant magneto-impedance (GMI) effect of Co69Fe5.5Ni1Si14.5-xPxB10 (x = 0, 0.5, 1, 1.5, 2) amorphous alloys were investigated in detail. Thermal analysis shows that replacing Si with a small amount of P can increase the thermal stability of the amorphous alloys. The permeability of the samples with magnetic field annealing is about 150% higher than that of the samples with stress-relieve annealing. The stress-induced GMI (GSI) results show that when the applied tensile stress is 0 MPa, 100 MPa, and 300 MPa, the maximum GMI ratio of the 1 at. % P-doping alloy with magnetic field annealing first increases from 76.6% to 102.8% and then decreases to 82%. Under the optimized measurement conditions, the magnetic field response sensitivity ξ of the Co69Fe5.5Ni1Si13.5P1B10 ribbon reached to 35.3%/Oe, the GSI ratio reached 34.3%, which has significant improvement compared to that of the stress-relieve annealing samples. Therefore, the magnetic field annealing technique greatly improved the GSI effect of the Co-based amorphous alloys, and the results obtained show a new way to develop high-performance GSI sensor materials and can be used in the construction of stress sensors.

Tuning of Magnetoimpedance Effect and Magnetic Properties of Fe-Rich Glass-Coated Microwires by Joule Heating.

The influence of Joule heating on magnetic properties, giant magnetoimpedance (GMI) effect and domain wall (DW) dynamics of Fe75B9Si12C4 glass-coated microwires was studied. A remarkable (up to an order of magnitude) increase in GMI ratio is observed in Joule heated samples in the frequency range from 10 MHz to 1 GHz. In particular, an increase in GMI ratio, from 10% up to 140% at 200 MHz is observed in Joule heated samples. Hysteresis loops of annealed samples maintain a rectangular shape, while a slight decrease in coercivity from 93 A/m to 77 A/m, after treatment, is observed. On the other hand, a modification of MOKE hysteresis loops is observed upon Joule heating. Additionally, an improvement in DW dynamics after Joule heating is documented, achieving DW propagation velocities of up to 700 m/s. GMI ratio improvement along with the change in MOKE loops and DW dynamics improvement have been discussed considering magnetic anisotropy induced by Oersted magnetic fields in the surface layer during Joule heating and internal stress relaxation. A substantial GMI ratio improvement observed in Fe-rich Joule-heated microwires with a rectangular hysteresis loop and fast DW propagation, together with the fact that Fe is a more common and less expensive metal than Co, make them suitable for use in magnetic sensors.

Ultra-large giant magnetoimpedance effect by a 2D square spiral amorphous microwire

Giant magnetoimpedance (GMI) effect is suitable for application in magnetic field sensing technology due to its high sensitivity to magnetic field. Improving GMI effect through the optimization of some intrinsic properties such as component and domain structure of magnetic materials encounters great challenges. Inspired by the material-structure integrated design philosophy and metamaterial design paradigm, a joule-annealed Co68.7Fe4Si11B13Ni1Mo2.3 magnetic microwire with square spiral macrostructure is proposed here to tremendously enhance GMI ratio (∼43,000%) and magnetic field sensitivity (∼6300%/Oe), which smashes the restriction brought from the material itself on GMI effect intensity. The coupling effect of ferromagnetic resonance arising from intrinsic properties of the magnetic material itself and LC resonance induced by the inductance of the square spiral structure and the parasitic capacitance of the microstrip line proves to be responsible for the obtained ultra-large GMI effect. Moreover, considerable GMI performance can still be obtained above the ferromagnetic resonance frequency, broadening the operating frequency range and breaking the restriction caused by the single ferromagnetic resonance. These make the square spiral microwire an excellent candidate for sensing application. This work provides a new and comprehensive approach of material-structure integrated design with the superiority of symphony of material itself and macro-configuration to realize ultra-large GMI effect.

Development of Magnetically Soft Amorphous Microwires for Technological Applications

Amorphous magnetic microwires can be suitable for a variety of technological applications due to their excellent magnetic softness and giant magnetoimpedance (GMI) effect. Several approaches for optimization of soft magnetic properties and GMI effect of magnetic microwires covered with an insulating, flexible, and biocompatible glass coating with tunable magnetic properties are overviewed. The high GMI effect and soft magnetic properties, achieved even in as-prepared Co-rich microwires with a vanishing magnetostriction coefficient, can be further improved by appropriate heat treatment (including stress-annealing and Joule heating). Although as-prepared Fe-rich amorphous microwires exhibit low GMI ratio and rectangular hysteresis loops, stress-annealing, Joule heating, and combined stress-annealed followed by conventional furnace annealing can substantially improve the GMI effect (by more than an order of magnitude).

Vol4 num4-16 Magnetic properties and applications of glass-coated ferromagnetic microwires

The impact of post-processing on soft magnetic properties and the giant magnetoimpedance (GMI) effect of Fe- and Co-based glass-coated microwires is evaluated. A remarkable improvement of magnetic softness and GMI effect is observed in Fe-rich glass-coated microwires subjected to stress annealing. Frequency dependence of GMI ratio of stress-annealed Fe-rich microwires has been discussed considering frequency dependence of the skin penetration depth, δ, as well as magnetic anisotropy distribution within the metallic nucleus. Annealed and stress-annealed Co-rich microwires present rectangular hysteresis loop and single and fast domain wall propagation. However, Co-based stress-annealed microwires present high magnetoimpedance ratio. Observed stress-induced anisotropy and related changes of magnetic properties are discussed considering internal stresses relaxation and “back-stresses”.

Magnetic properties and giant magneto-impedance effect of FINEMET/IGZO composite ribbons

In order to study the magnetic properties and giant magnetoimpedance (GMI) effect of FINEMET/IGZO composite ribbons. A series of ZnGaInO4 film (IGZO) with different thickness (t) were deposited by RF magnetron sputtering from targets of nominally identical compositions onto Fe-based nanocrystalline ribbon. The results of hysteresis loops show that the FINEMET/IGZO composite ribbons has good soft magnetic properties, and the GMI ratio of the composite ribbons are enhanced. The GMI ratio of FINEMET/IGZO composite ribbons increases at first and then decreases with the increase of IGZO layer thickness (0 ∼ 200 nm). This result was attributed to the relative contribution of electromagnetic interaction and stress interaction between IGZO coating layer and FINEMET ribbon. These results provide a method for improving the GMI effect in composite ribbons, optimizing the GMI effect of semiconductor materials and exploring new GMI magnetic sensors compatible with semiconductor electronics.

Tunable Linear Dependence of Giant Magnetoimpedance Response of Microwires Annealed under Fluid Oil for Sensor Applications

Herein, fluid oil joule annealing modulation (FOJA) for improving the giant magnetoimpedance (GMI) property of CoFe‐based microwires with the microstructure is adopted, and magnetic domain structure is systematically investigated. Compared with general joule annealing (JA) method, a much larger DC current can be used. The maximum GMI value is 440.8% in the 250 mA FOJA‐treated sample and the maximum monotonically increasing magnetic field is 12 Oe in 400 mA FOJA‐treated sample. In the 100–400 mA FOJA‐treated samples, there is a nearly linear increase and decrease relationship between GMI and the magnetic field. In addition, the FOJA method can control the radial stress release and helical magnetic domains of the microwire by changing the Joule heat transfer and the circumferential magnetic field and then tune the GMI performance of the microwires. The remarkable features, including a continuous and clear linear‐sensitive response field Hex of 0–95 Oe, quick response sensitivity, large GMI ratio, and excellent tunability, make the FOJA‐tailored microwires promising candidate material for miniaturized GMI sensors.

Effect of Meander Structure on Magnetoimpedance Characteristics in FeNi/Cu/FeNi Films

The three-dimensional physical models for FeNi/Cu/FeNi films with two different types of structures which are linear and meander are developed. The relationship between the impedance of the films and the applied magnetic field or excitation frequency is obtained and the influence of geometric parameters and structures of the films on the giant magnetoimpedance (GMI) effect is analyzed. The result shows that the GMI effect in the film with a horizontal meander structure appears to be much stronger compared with that in a linear structure. The negative mutual inductance of the meander FeNi/Cu/FeNi films reduces the total inductance and decreases frequency response. Meanwhile, the GMI effect and the negative mutual inductance are enhanced by increasing the number of turns or decreasing the space width between each segment. Based on these effects, the FeNi/Cu/FeNi film with a vertical meander structure is proposed and simulated, which reflects the design of the meander structure in the thickness direction. The distance between each segment is reduced to 500 nm. The GMI effect and the negative mutual inductance are greatly enhanced (the maximum value of the GMI ratio increases from 207% to 1247% when the excitation frequency changes from 50MHz to 300MHz). Furthermore, the spatial resolution of the film is further improved. The results obtained could be useful both for a better understanding of the GMI effect of the FeNi/Cu/FeNi film with a meander structure and for providing a choice for the device preparation of highly sensitive magnetic sensors.

Tailoring of Magnetic Softness and Magnetoimpedance of Co‐Rich Microwires by Stress Annealing

Herein, detailed studies on the influence of stress annealing on the magnetic softness and giant magnetoimpedance (GMI) ratio of Co69.2Fe3.6Ni1B12.5Si11Mo1.5C1.2 glass‐coated microwires are provided. As‐prepared microwire presents linear hysteresis loops, moderate GMI ratio with double‐peak magnetic field dependence and low coercivity (4 A m−1), typically observed for wires with transverse magnetic anisotropy. However, after conventional annealing magnetic hardening and transformation of linear hysteresis loop into rectangular with coercivity about 90 A m−1 is surprisingly observed. It is shown that stress annealing allows preventing magnetic hardening and remarkably improving GMI ratio. Properly stress‐annealed samples present better magnetic softness: almost unhysteretic loops with coercivity about 2 A m−1 and magnetic anisotropy field about 35 A m−1. Observed stress‐annealing‐induced anisotropy is affected by the tensile stresses, applied during annealing and by the annealing temperature. From the frequency dependence of the maximum GMI ratio, the optimum frequency ranges for as‐prepared and stress‐annealed samples are determined. The observed stress‐annealing‐induced magnetic anisotropy and associated changes in magnetic properties and GMI effect are discussed in terms of internal stresses relaxation and related modification of the magnetostriction coefficient, “back stresses,” structural anisotropy, redistribution of internal stresses, and change of spatial distribution of magnetic anisotropy.

Optimization of the high-frequency magnetoimpedance response in melt-extracted Co-rich microwires through novel multiple-step Joule heating

The optimization of the high frequency giant magnetoimpedance (GMI) effect and its magnetic field sensitivity in melt-extracted Co 69.25 Fe 4.25 Si 13 B 12.5 Nb 1 amorphous microwires was systematically studied through a multi-step Joule annealing (MSA) technique. The surface morphology, microstructure, surface magnetic property, and radio frequency GMI response of the Co-rich microwires were explored using techniques like microscopy, magneto-optical Kerr effect (MOKE) magnetometry, and the magnetic field dependence of the wire's radio frequency impedance (GMI). The multi-step Joule annealing protocol begins with an initial dc current amplitude ( i dc ) of 20 mA that was stepped up by 20 mA every 10 min to a maximum amplitude of 300 mA. Radio frequency GMI measurements at 20 MHz demonstrated a remarkable improvement of the GMI ratio and field sensitivity to 760% (1.75 times of that of the as-prepared wire) and 925%/Oe (more than 17.92 times of that of the as-prepared wire), respectively, after the MSA protocol with a maximum current amplitude of 100 mA. Microscopy and MOKE suggest that the MSA technique can enhance the microstructure and surface magnetic domain structure of the Co-rich magnetic microwire, which would give rise to an improved GMI ratio. The high GMI sensitivity at small magnetic fields renders these MSA-treated Co-rich microwires highly promising materials for biomedical devices that sense and monitor small, biological magnetic fields.