Giant Magnetoimpedance Research Articles

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.

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.

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”.

Магнитный импеданс пленочных наноструктур для оценки полей рассеяния микрочастиц магнитных композитов

Longitudinal giant magnetoimpedance effect of [Fe21Ni79/Cu]5/Cu/[Fe21Ni79/Cu]5 film element was investigated depends on stray magnetic field of epoxy magnetic composite with 30 % weight concentration of iron oxide magnetic microparticles. Configuration of an experiment was a model of thrombus detection in a blood vessel. Stray magnetic field was varied by movement of a magnetic composite above the element perpendicular to the long side. Composite was either magnetized or not to the state of remanence. As the magnetic composite approaches the GMI element, MI ratio curves are smoothed and shifted along the field axis and maximum value of the MI ratio decreases. Magnetic properties of magnetic composite and film element were investigated as well.

Planar ensembles of multilayer film microelements based on Cu/FeNi components

Planar ensembles of multilayer periodic square microelements of the type [Cu(6 nm)/FeNi(100 nm)]5 were obtained by ion-plasma sputtering on glass substrates using mesh copper masks. The surface features of trace elements were analyzed using a stylus profilometer, optical and scanning electron microscopy. Static magnetic properties and features of the magnetic domain structure were studied using the magneto-optical Kerr effect. The resulting planar ensembles can be used as an integral part of the film elements of weak magnetic field detectors operating on the basis of magnetic impedance (MI) to increase the sensitivity of the MI response to an external magnetic field. Keywords: multilayer film structures, ensembles of trace elements, periodic structures, giant magnetoimpedance effect. Keywords: multilayer film structures, ensembles of trace elements, periodic structures, giant magnetoimpedance effect.

Regulation mechanism of giant magneto-impedance effect of multi-field coupling Fe-based alloy

Fe-based amorphous and nanocrystalline alloys are considered as the preferred dual-green energy-saving materials due to their unique magnetic properties, such as high permeability, low coercivity, and near-zero saturation magnetostriction. As such, they have received extensive attention in applications like magnetic core material for high-frequency transformers, common model chokes, ground fault interrupters, and rotors in motors, over the past decades. In this work, Fe<sub>64.8</sub>Co<sub>7.2</sub>Nb<sub>4</sub>Si<sub>4.8</sub>B<sub>19.2</sub> (in atom percent) amorphous alloy ribbons are prepared by using the single roller quenching method, then subsequently subjected to multi-field coupling heating treatment in the air which includes heating by Joule heating effect and tensile stress field. Furthermore, the longitudinally driven giant magneto-impedance effect and magnetic domain structures of ribbons are observed by using 4294A impedance analyzer and magnetic force microscopy, respectively. The magneto-crystalline anisotropy field and stress anisotropy field of ribbons are analyzed by using X-ray diffraction, random anisotropy model, and numerical fitting. Meanwhile, the concept of magnetic anisotropy competing factor (<i>k</i>) is proposed, from the viewpoint of magnetic anisotropy, a mechanism for regulating giant magneto-impedance effect of ribbons prepared with multi-field coupling is studied. It is found that the longitudinally driven giant magneto-impedance effect gradually transforms from the single peak to dome-like with tensile stress increasing. However, a spike and dome-like giant magneto-impedance effect appears during such transformation, which is composed of two parts: spike-like top and dome-like base. Based on the magnetic domain structure of ribbons, it is found that the typical stress-annealed transversal magnetic domain structure is observed in ribbons of <inline-formula><tex-math id="Z-20221115160531">\begin{document}$k \leqslant 0.147$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="23-20221376_Z-20221115160531.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="23-20221376_Z-20221115160531.png"/></alternatives></inline-formula>, while nucleation and splitting phenomenon of new domains are observed at the transversal magnetic domain wall in ribbons of <i>k</i> > 0.147. Both longitudinally driven giant magneto-impedance effect and domain structures provide evidence to support the competing inhibition effect of magnetic anisotropy which exists in Fe-based alloy ribbon. Therefore, it is suggested that Fe-based alloys exhibit excellent stress-sensitive properties that can be understood by the competing inhibition effects of magnetic anisotropy. It is further shown that the competing inhibition effect of magnetic anisotropy is the main reason for regulating the giant magneto-impedance effect of soft magnetic materials. This multi-field coupling Fe-based alloy has good application prospects in regulating magnetic properties of magnetic materials.

Magnetic impedance of film nanostructures for stray magnetic field evaluation of microparticles in magnetic composites

Longitudinal giant magnetoimpedance effect of [Fe21Ni79/Cu]5/Cu/[Fe21Ni79/Cu]5 film element was investigated depends on stray magnetic field of epoxy magnetic composite with 30% weight concentration of iron oxide magnetic microparticles. Configuration of an experiment was a model of thrombus detection in a blood vessel. Stray magnetic field was varied by movement of a magnetic composite above the element perpendicular to the long side. Composite was either magnetized or not to the state of remanence. As the magnetic composite approaches the GMI element, MI ratio curves are smoothed and shifted along the field axis and maximum value of the MI ratio decreases. Magnetic properties of magnetic composite and film element were investigated as well. Keywords: Magnetoimpedance effect, multilayered film nanostructures, composite materials, biodetection.

Soft Magnetic Properties and Giant Magneto-Impedance Effect of Co68.15fe4.35si12.5b15-Xcrx Amorphous Ribbons

Soft Magnetic Properties and Giant Magneto-Impedance Effect of Co68.15fe4.35si12.5b15-Xcrx Amorphous Ribbons

Distinguish exchange coupling and dipolar interaction in FINEMET/FePt/FePd composite ribbons

In magnetic materials, the exchange coupling and dipolar interaction can significantly influence the magnetization processes, which was addressed in this paper by studying the system of FePt/FePd film deposited on FINEMET ribbon. In FINEMET/FePt/FePd composite ribbons, Giant magnetoimpedance effect (GMI) increased due to the contribution of the exchange coupling and dipolar interaction to the bias field (Hb) and resulted in an asymmetric characteristic of the GMI curves. Magneto-optical Kerr effect (MOKE) microscopy revealed typical transverse and longitudinal magnetic domain structure in FINEMET ribbon and FePd film respectively. Consequently, the FePd coating layer generated a Hb to the FINEMET ribbon and induced the asymmetry of GMI curves. The results also revealed that the generation of the Hb is mainly due to the exchange coupling and dipolar interaction between FePt, FePd coating layer and FINEMET ribbon. These two interactions can be clearly distinguished by exchange coupling and dipolar interaction models, which provides a valuable tool to study of the impact of the Hb on magnetic materials and could also extend the promise applications of AGMI in MI-based sensor devices.

Improvement of high frequency giant magnetoimpedance effect in CoFeSiB amorphous ribbon with vanishing magnetostriction by electrodeposited Co coating surface layer

The influence of a ferromagnetic cover layer on giant magnetoimpedance (GMI) effect in nearly-zero magnetostrictive Co66.5Fe3.5Si12.0B18.0 amorphous ribbon after being surface coated by an electrodeposited Co layer of 10 μm in thickness, has been studied in the high frequency range between 10 MHz and 1.5 GHz. Longitudinal MOKE measurements performed on both kind of samples reveal the influence of exchange coupling interaction at the interface between the magnetic amorphous ribbon and electrodeposited Co coating layer, which is sensitive to the skin depth effect at high ac current frequency values. Comparison between GMI responses of the Co coated amorphous ribbon and the as-cast sample is provided. A more sharp and well defined double-peaks dependence of impedance on magnetic field, but with lower peaks intensity, is observed for the Co coated ribbon in the frequency range of 10–100 MHz, while the peaks intensity is higher than that observed in the as-cast ribbon at the high frequency value of 1 GHz due to the higher resistance of the Co electroplated layer than the core one. The influence of a dc bias drive current on the GMI response in both amorphous ribbons (as-cast and Co layered) is analyzed, which originates the removal of magnetic domain structure from both, the as-cast and Co-coated ribbons, giving rise more sensitive GMI effect. CoFeSiB amorphous ribbon with vanishing magnetostriction can achieve improved high frequency magnetic properties after being surface coated with electrodeposited ferromagnetic layers, as outstanding candidates for electromagnetic and magnetomechanical engineering applications.

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.

Improvement of Giant Magnetoimpedance and Sensitivity in Co68.5-xFe4WxSi16.5B11 (x = 0.8, 2) Ribbons Sandwiched in PVA/Fe3O4 Nanocomposite Films

Improvement of Giant Magnetoimpedance and Sensitivity in Co68.5-xFe4WxSi16.5B11 (x = 0.8, 2) Ribbons Sandwiched in PVA/Fe3O4 Nanocomposite Films

Enhanced asymmetric giant magneto-impedance effect and linearity in sandwich FePd/FINEMET/FePd composite ribbons

The FePd/FINEMET/FePd composite ribbons with sandwich structure were designed by magnetron sputtering. The morphology, magnetic properties and asymmetric giant magneto-impedance (AGMI) effect of FePd/FINEMET/FePd composite ribbons show that the sandwich structure can significantly improve the GMI effect of FINEMET ribbon with a homogeneous structure. Results have demonstrated that the magnetic dipole interaction between the FePd layer and the FINEMET ribbon makes the FePd/FINEMET/FePd composite ribbons obtain a larger GMI effect at low frequencies. The maximum GMI ratio of FePd/FINEMET/FePd composite ribbons reaches 51 %, which is 2.2 times that of bare FINEMET ribbon. The asymmetry degree of GMI curves is up to 85 %. It has the ability to significantly enhance the GMI effect, linearity and reduced the characteristic frequency of composite materials. The experimental results can be explained by the magnetic dipole interaction model. It is a profound significance in the development of a magnetic sensor that can increase the GMI ratio and the linearity.

Performance of giant magneto-impedance effect of CoFeSiB films on different substrates

Reports on the influence of the stress on giant magnetoimpedance (GMI) effect of CoFeSiB films are rarely seen. Therefore, the influence of stress on the GMI effect of CoFeSiB thin-film was studied in this investigation. Firstly, to select suitable substrates for applying stress, CoFeSiB films were fabricated on different flexible substrates with magnetron sputtering, and the hysteresis loops of the films were measured. The results show that the magnetic properties of the films on polyester (PET) substrates and silicate flexible glass are similar and better than polyimide (PI). So they are candidate materials for flexible substrates. And then, the GMI curves of the films under different stresses were measured. The results show that applying longitudinal tensile stress would reduce the longitudinal anisotropy and weaken the GMI effect of the CoFeSiB film. The research on the influence of stress on GMI thin-film would be helpful to fabricate flexible GMI sensors of stable performance.

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.

Noise analysis of a high sensitivity GMI sensor based on a Field-Programmable-Gate-Array

In this article, an analysis of noise sources and their impact on the overall noise performance in a digitally conditioned and high sensitivity Giant Magneto-Impedance (GMI) sensor is proposed. The digital conditioning is based on a Direct Digital Synthesizer (DDS) and a Digital-Down-Converter (DDC) fully implemented in real time using a Field-Programmable-Gate-Array (FPGA). The noise analysis considers the equivalent magnetic noise, which limits the detection resolution. An analytical model is developed to quantify the voltage noise spectral density of each noise source involved in the digital GMI sensor and its contribution to this total equivalent magnetic noise in the white noise region. The equivalent magnetic white noise level expected by this model fits the measurement. For a sensing element in off-diagonal configuration, made up of a 400 turns coil wound around a 2.5 cm Co-rich GMI wire, equivalent magnetic noise of 33 pT/Hz and 1.8 T/Hz were obtained at 1 Hz and in the white noise region, respectively. Some rules to improve these promising performances are discussed.

Effect of Joule heating on giant magnetoimpedance effect and magnetic properties of Co-rich microwires

The effect of Joule-heating on hysteresis loops and giant magnetoimpedance effect, GMI; of Co69.2Fe3.6Ni1B12.5Si11Mo1.5C1.2 glass-coated microwire is studied. Joule heating performed at suitable conditions prevents the magnetic hardening observed during conventional furnace annealing of the studied microwires. A remarkable GMI ratio improvement is observed as compared to as-prepared annealed and even stress-annealed microwires. Observed magnetic softening and GMI ratio improvement have been discussed considering magnetic anisotropy induced by Oersted magnetic field during Joule heating and internal stresses relaxation.

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.

Contactless magnetic nanoparticle detection platform based on non-linear GMI effect

A detection platform based on non-linear Giant Magnetoimpedance Effect was analyzed for the design of a contactless and low-cost detector of magnetic nanoparticles. The sensor consists of two soft magnetic amorphous wires (Co66Fe2Si13B15Cr4, 1.5 cm in length) placed in parallel and connected electrically in series. Initially, a simple voltage divider was employed to characterize the variations of the first, V1fand second harmonic, V2f, voltages. Their response was analyzed under the effect of the remnant magnetic field generated by different amounts of Fe3O4 nanoparticles (mean diameter 140 nm) as a function of an external magnetic field, H. Due to the larger relative variations showed by V2f, the second harmonic was chosen for the final prototype development. An electronic interface was designed for both current excitation and V2f detection. The designed detection platform, characterized by high detection sensitivity, low-cost, portable, and reusable features, can be employed to efficiently detect magnetic nanoparticles.