Maximum Giant Magnetoimpedance Ratio Research Articles

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.

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.

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.

Investigation of the giant magneto-impedance effect of single crystalline YIG based on the ferromagnetic resonance effect

We investigated the giant magneto-impedance (GMI) effect on ferrimagnetic insulator yttrium iron garnet (YIG) films and spheres, and the ferromagnetic resonance effect played a vital role. The GMI results were derived from the high-frequency measurements of a microwave transmission line loaded with YIG films and spheres. Our findings showed that there were obvious distinctions in the impedance of the transmission line loaded with single crystalline YIG samples depending on the external magnetic field, which indicates the significant GMI effect. The maximum GMI ratio as high as 256% was achieved, corresponding to a magnetic response of 8.8%/Oe. This study reveals that single crystalline YIG films are promising candidates for using as probe element in chip-scale magnetic sensors.

Enhanced giant magneto-impedance effects in sandwich FINEMET/rGO/FeCo composite ribbons

This paper designed and regulated a unique sandwich FINEMET/rGO/FeCo composite ribbons (/F/GFC) with giant magneto-impedance (GMI) effect. The reduced graphene oxide (rGO) was synthesized on the FINEMET ribbons by one-step electroless plating, and FeCo layer was obtained by magnetron sputtering method. The study on morphology, structure, GMI effect and magnetic properties of /F/GFC illustrated that the currents passed through the highly conductive layer of rGO at high frequency, which greatly reducing the skin effect. In addition, the FeCo layer increased the permeability and provided a closed magnetic circuit, which can finally gain a large GMI effect at low frequency. The /F/GFC owned enhanced GMI effect, with the maximum GMI ratio reaching 70.32%, which was 2.1 times of the bare FINEMET ribbon, 1.4 times of the FINEMET/rGO composite ribbon and 1.2 times of the FINEMET/FeCo composite ribbon, respectively. The result can be explained by the regulating effect of magnetic dipole interaction on the magnetic properties of soft magnetic materials.

Investigation the influence of structure parameters on giant-magnetoimpedance effect measured by non-contact method

Purpose This paper aims to investigate the influence of structure parameters on giant-magnetoimpedance (GMI) effect measured by non-contact method. Design/methodology/approach The GMI sensor contains a Co-based internal magnetic core fabricated by laser cutting and an external solenoid. The influences of magnetic permeability of magnetic core and structure parameters on GMI effect were calculated in theoretical model. The output impedance, resistance, reactance and GMI ratio were measured by non-contact method using impedance analyzer. Findings Enhancing external magnetic field intensity can decrease the magnetic permeability of core, which has vital influences on the magnetic property and the output response of GMI sensor. In addition, increasing the width of magnetic core and the number of solenoid turns can increase the maximum GMI ratio. The maximum GMI ratio is 3,230% with core width of 6 mm and solenoid turns of 200. Originality/value Comparing with traditional contact-measured GMI sensor, the maximum GMI ratio and the magnetic field sensitivity are improved and the power consumption is decreased in non-contact measured GMI sensor. GMI sensor measured by non-contact method has a wide range of potential applications in ultra-sensitive magnetic field detection.

Giant magnetoimpedance and magneto-optical Kerr effects in (Co63Ni37)75Si15B10 amorphous ribbon

The Giant magneto-impedance (GMI) effect in the frequency range 10–1000 MHz and surface magnetic characterization using the magneto-optical Kerr effect (MOKE) in (Co63Ni37)75Si15B10 amorphous ribbon were studied. The GMI ratio increases with a frequency up to around 500 MHz followed by a slow decrease. Observed dependence of GMI ratio is discussed by considering the frequency dependencies of the skin depth penetration and magnetic permeability. MOKE in the transverse and longitudinal applied magnetic field to the ribbon direction configurations provides images of magnetic domain structure and hysteresis loops of the two surface sides of the ribbon. An inclined magnetic structure with respect to the longitudinal direction of the ribbon was observed. This inclined magnetic structure is related to a significant transverse component of the magnetic susceptibility tensor, which is a prerequisite to observe GMI effect. The magnetic anisotropy field evaluated from the hysteresis loop with the transverse applied magnetic field configuration is in agreement with the longitudinal magnetic field necessary to obtain the maximum GMI ratio. The MOKE characteristic of two sides ribbon is quite vertical associated to large Barkhausen jumps because the anisotropy axis is, in this configuration, parallel to the applied magnetic field.

Route of magnetoimpedance and domain walls dynamics optimization in Co-based microwires

The influence of post-processing (annealing and stress-annealing) on the magnetic softness, Giant magnetoimpedance (GMI) effect and domain wall dynamics of Fe3.6Co69.2Ni1B12.5Si11Mo1.5C1.2 glass-coated microwires is studied.As-prepared Co-rich glass-coated microwire presents linear hysteresis loops and rather higher magnetoimpedance ratio with double-peak magnetic field dependence, typical for materials with transverse magnetic anisotropy.Considerable magnetic hardening and transformation of linear hysteresis loop with low coercivity (Hc ≈ 4 A/m) into rectangular with Hc ≈ 90 A/m upon annealing without stress is observed. However, we observed remarkable MI effect improvement at certain annealing conditions.Stress-annealing of studied microwire allows considerable magnetoimpedance ratio and domain wall velocity increasing. Additionally, remanent magnetization growth and coercivity decrease are generally observed upon stress annealing. Frequency dependence of maximum GMI ratio for as-prepared and annealed samples is evaluated. The obtained frequency dependence of the maximum GMI ratio allows determination of the optimal GMI measurement conditions for each sample. The observed stress-induced anisotropy and related changes in magnetic properties are discussed considering the internal stresses relaxation and “back-stresses”.

Magnetic properties and giant magneto-impedance effect in electroless-deposited CoP/Cu composite wires

The influence of deposition parameters on the structure and magnetic properties of CoP/Cu composite wires had been studied systematically in this paper. These parameters hold a significant effect on the surface topography, coating composition, deposition rate, magnetic properties and giant magnetoimpedance (GMI) effect of the composite wires. The CoP/Cu composite wire is layered clearly, the coating is uniform and the soft magnetic properties is excellent, the largest value of field sensitivity (ξ) is 195%/Oe and the maximum GMI ratio is 902%, which is the highest GMI value of the CoP composites materials so far. This result will be great significance for further study of the application of magnetic sensors.

Soft ferromagnetic amorphous microwires for GMI sensing cores

Abstract The recent work is focused on the development of suitable amorphous ferromagnetic microwires (CoFe-based) for use in giant magneto-impedance (GMI) magnetic sensing cores. Rapid solidification route is used for the preparation of microwires via in-rotating water quenching technique. The potential of the CoFeSiBCr soft magnetic microwires for GMI based sensing core is investigated by using the driving frequency of MHz range. The GMI characteristics of the developed materials are carried out via impedance-mode. The performance of the magnetic sensor is studied based on its maximum GMI ratio, magnetic field sensitivity and noise spectrum. The experimental results reveal that the maximum GMI ratio, GMImax of about 650% and field sensitivity of around 802 V/T is achieved at ac driving frequency of 5 MHz with 3 mA driving current when annealed at 750 K for 5 min. The noise level of the optimized microwire can be obtained under 10 nT/√Hz@1 Hz while driven at 5 MHz. By means of its high operating frequency regime, high sensitivity, low noise level and simple methodology for sensing, the GMI microwires working in impedance-mode can be a potential candidate for commercial sensing applications such as microfluxgate sensors.

Optimized giant magneto-impedance effect in electroless-deposited NiFeP/Cu composite wires

In this work, NiFeP/Cu composite wires were fabricated by electroless deposition. The preparation parameters have been comprehensively investigated, including metallic salt ratio of FeSO4 to (FeSO4+NiSO4), concentration of NaH2PO2, pH value and deposition temperature. These parameters showed significant influence on the surface morphology, magnetic properties and giant magnetoimpedance (GMI) effect. As a consequence, the optimal bath composition and deposition conditions were obtained, resulting in the maximum GMI ratio (ΔZ/Z)max of 1103% at 1MHz. The optimized composite wires have showed practical potential in the application of magnetic sensors.

Engineering of magnetic softness and giant magnetoimpedance effect in Fe-rich microwires by stress-annealing

Magnetic softness and giant magnetoimpedance (GMI) effect of Fe-rich microwires has been considerably improved by stress-annealing: we obtained maximum GMI ratio about one order higher than in as-prepared Fe-rich microwire and of the same order as in as-prepared Co-rich microwire. High enough bias current allows drastic increasing of GMI ratio of Fe-rich microwires up to 120% and off-diagonal GMI effect but also produces irreversible changes of GMI effect related to Joule heating of the samples. For interpretation of observed dependences we considered internal stresses relaxation after annealing interplay of compressive “back-stresses” arising after stress annealing and axial internal stresses.

Magnetic properties and magnetoimpedance of FeCoNi/CuBe electroplated tubes with different features of field-annealing induced magnetic anisotropy

The effect of field annealing (in direct (DC) or alternating current (AC) field) on the structure, magnetic properties and giant magnetoimpedance (GMI) of CuBe/ Fe19Co17Ni64 electroplated tubes was studied. The field and frequency dependences of total impedance and its real part were comparatively analyzed together with magnetization processes features. The GMI sensitivity with respect to an applied field was the subject of special attention in view of possible applications of these materials in small magnetic field sensors. The maximum GMI ratio depends strongly on the heat treatments. The DC field annealing leads to the highest total impedance GMI ratio (ΔZ/Z=250%) and real part of the total impedance GMI ratio (ΔR/R=640%), compared to as-cast and AC field annealed samples. The external field response of DC annealed samples presented a single peak GMI response as a consequence of a strong contribution of the longitudinal effective anisotropy. At the same time, the maximum obtained sensitivity of 13.5%/Oe for DC case is much lower compared to the highest sensitivity values obtained for as-prepared (28.6%/Oe) and DC field annealed (22.0%/Oe) tubes for the low frequency of 2.5MHz. The weak dependence of ΔZ/Z ratio in the case of AC field annealed samples in the high frequency range is an important advantage for particular sensor applications.

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.

Domain Transformation and MI of Melt-extracted Co68.15Fe4.35Si12.25B13.25Nb1Cu1 Microwires by Cryogenic Joule Annealing

Giant magneto-impedance (GMI) effect and domain transformation for melt-extracted Co68.15Fe4.35Si12.25B13.25Nb1Cu1 amorphous wires have been induced by a cryogenic Joule annealing (CJA) treatment with different DC current amplitude (0~350 mA) for 240s. Experimental results indicate that the maximum GMI ratio ([ΔΖ∕Ζ0]max) achieves to 188.1% with exciting field increasing to 1.8 Oe monotonically for 300 mA annealing treated wires, which can attribute to the surface complex domain structure change formed by CJA treatment. The liquid nitrogen can protect the wire from crystallization when applied large DC currents. Moreover, the CJA treatment can improve the response sensitivities effectively. These remarkable characteristics make the melt-extracted microwires by CJA tailoring as the promising candidate material for small-sized magnetic sensors.

Soft magnetic properties and giant magnetoimpedance effect in thermally annealed amorphous Co68Fe4Cr3Si15B10 alloy ribbons

Giant magnetoimpedance (GMI) effect in amorphous soft magnetic materials has been intensively investigated owing to its promising technological applications. The GMI effect can be improved when an amorphous ferromagnetic material is subjected to proper heat treatments. In present work, in order to further improve the GMI effect in amorphous Co68Fe4Cr3Si15B10 ribbons, thermal annealing is employed to optimize the GMI effect of amorphous Co68Fe4Cr3Si15B10 ribbons. Magnetic measurements show that the soft magnetic properties of ribbons were affected significantly by thermal annealing. The saturation flux density of ribbons increases with increasing annealing temperature. Optimized annealing temperature of about 400°C gives lowest coercivity, highest permeability and electric conductivity. The frequency dependence of GMI effect in annealed Co68Fe4Cr3Si15B10 ribbons is discussed in details. The maximum GMI value of about 220% and sensitivity of about 106%/Oe were achieved at the driven frequency of 3MHz in the ribbon annealed at 400°C. It is clear that the enhanced maximum GMI ratio and sensitivity for the sample annealed is caused by its increased saturated flux density, permeability, electrical conductivity and reduced coercivity.

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.

Giant magnetoimpedance effect enhanced by thermoplastic drawing

We performed thermoplastic forming (TPF) on FeCoNbB metallic glass ribbons with a supercooled liquid region exceeding 100 K, and found the sample after TPF is still completely amorphous. More importantly, the giant magnetoimpedance (GMI) effect was improved after the forming process: the maximum GMI ratio and sensitivity increased from 41% to 12.3%/Oe in the case of as-cast sample to 280% and 358.2%/Oe in the case of resulting sample after TPF, respectively. The hysteresis loops and domain patterns were subsequently studied, which revealed that the primary factor leading to the improvement of the GMI effect was the enhanced longitudinal magnetic anisotropy induced by the TPF process. We therefore assume that TPF is an effective way that improves the GMI effect, which differs from conventional annealing methods.

Cryogenic Joule annealing induced large magnetic field response of Co-based microwires for giant magneto-impedance sensor applications

We have presented herein the results of microstructure, surface magnetic domains (SMDs), and giant magneto-impedance (GMI) effect of melt-extracted Co68.15Fe4.35Si12.25B11.25Nb2Cu2 amorphous wires for the first time employed by using a cryogenic Joule annealing (CJA) technique with large DC current amplitude. Compared with the conventional JA method, experimental results indicate that the maximum GMI ratio [ΔZ/Z0]max achieves up to 425% at 8.1 MHz with monotonic increase of the axial magnetic field Hex up to 6.5 Oe for 300 mA (equal to around 1.06 × 106 A/dm−2) CJA-ed wire, which is about 75% larger than the [ΔZ/Z0]max for the 100 mA (nearly 3.53 × 105 A/dm−2) JA-ed microwires. The remarkable features of large and linearly sensitive response field (2.5 ∼ 6.5 Oe) and the sensitivity of 99.4%/Oe with higher GMI ratio simultaneously make the CJA tailored melt-extracted microwires promising candidate materials for miniaturized GMI sensors. Another interesting result of GMI profiles of 200 mA (appropriately equal to 7.07 × 105 A/dm−2) CJA-ed wire show a linear response to Hex (ranging from 10 to 80 Oe or more), this behavior of GMI curves can be explored to fabricate bi-sensor. Large response field proves to originate from the intensive coupling between the radial stress field and the circumferential magnetic field during CJA process. The effect of outer-shell microstructure and complex SMD for 300 mA CJA-ed microwire is attributed to the fact that liquid nitrogen hinders the evolution of circumferential domain structure to some extent and protects the amorphous structure in the shell region.

Magneto-Impedance Effect of Composite Wires Prepared by Chemical Plating under DC Current

Abstract CuBe composite wires of 100 μm in diameter coated with a layer of NiCoP were prepared by a chemical plating method under DC current (CPUDC). The influences of DC current on coating morphology, deposition rate, composition, giant magneto-impedance (GMI) effect and magnetic properties were investigated. It was shown that the circumferential domain structure of coating layer was induced by the DC current going through the wires. A maximum GMI ratio of 870% was obtained in the composite wire prepared under 150 mA and tested at 180 kHz. It is 30 times higher than that of the composite wire plated in the same condition by conventional chemical plating method, indicating that CPUDC is an easy and effective approach to obtain composite wires and its applications will be further extended on magnetic sensors.