Co-based Amorphous Ribbons Research Articles

Surface magnetic properties and giant magnetoimpedance effect in Co-based amorphous ribbons

Correlationship between surface magnetic properties studied using the MOKE technique and giant magnetoimpedance effect (GMI) of nearly-zero magnetostrictive Co66.5Fe3.5Si12.0B18.0 amorphous ribbons in as-cast state has been investigated in the frequency range of 10 MHz–1.5 GHz. It was found that the surface anisotropy is different in the sides of the ribbon: it is transversal to the ribbon axis with multiple domain walls in one side and axial with a single domain wall in the other. The effect of permanent bias current on surface domain structure was investigated and it was found that the multidomain transversal is very sensitive to the bias current while the axial anisotropy is practically not affected by the applied bias current. This finding can be applied in design of highly sensitive material for magnetic sensors.

软磁非晶薄带磁滞回线偏移行为研究

本文通过观测钴基、铁基非晶薄带的非对称磁滞回线现象，摸清了产生该现象的基本条件，在深入研究了与此现象密切相关的各向异性、局域磁矩和磁畴的变化的基础上；阐明了这种非晶薄带的回线偏移行为的基本机制；最后还尝试研究了一种有效调控偏移场的技术方法。 In this dissertation, the formations of displaced loops behavior were obtained by studying series of Co-based and Fe-based amorphous ribbons. And the relevant factors including induced magnetic anisotropy, magnetic domain and torque were investigated. Further, the main origin of loop shift of ribbons was clearly explained. Finally, we also tried to find a way, by which the shift field can be modulated.

Reverse Optimization of an Integrated Solenoid Fluxgate Sensor Based on Co-based Amorphous Soft Magnetic Ribbon

In this paper, based on the sensitivity empirical formula, the microsolenoid fluxgate sensor is designed in reverse by making use of optimized parameters. The fabricated microsolenoid fluxgate sensor with a Co-based amorphous ribbon core presents a best sensitivity of 3587 V/T, a power consumption of 20.35 mW, and a linear range of 0–100 μT. The test results show that the sensitivity of the sensor is in good agreement with the theoretical expectation, with an error lower than 4%. The improvement of the core material makes a major contribution to the high sensitivity. The noise power density of the sensor is 0.14 nT/√Hz@1 Hz at the frequency of 100 kHz and the noise rms level is 2.2 nT in the frequency range of 0.1–10 Hz. Reverse design provides a simple and rapid way to optimize the performance of the existing fluxgate sensor for different applications.

GMI field sensitivity near a zero external field in Co-based amorphous alloy ribbons: experiments and model

The giant magnetoimpedance (GMI) effect in Co66Fe4Ni1Si15B14 amorphous ribbons was investigated, and the obvious blunt peaks of GMI curves were observed in a weak external magnetic field (0~3 Oe). The shape of the blunt peaks could be changed by different treatments, such as changing the aspect ratio of the ribbons, premagnetization before magnetoimpedance measurement, and rapid heat-treatment, and the GMI sensitivity is improved. Based on the experimental results, a model in view of magnetostrictive energy is proposed to analyze the bluntness of the peak of the GMI curve and the process of transverse permeability varying with the external field near zero-field in the Co-based amorphous ribbons, and all the experimental results have good agreement with our model.

Enhanced GMI effect in tortuous-shaped Co-based amorphous ribbons coated with graphene

Enhanced giant magnetoimpedance (GMI) effect has been observed in micro-patterned Co-based Metglas 2705M amorphous magnetic ribbons coated with single-layer graphene. The micro-patterned ribbon was designed for tortuous structure and fabricated by MEMS technology, and the graphene thin film was developed by spin coating and dispensing method onto the surface of ribbon. Relative to the plain ribbon, at a measured frequency of 6 MHz and a field of 20 Oe, a 13.1 % enhancement of the maximum GMI effect was observed in the ribbon by spin coating graphene. However, there was a small change of the GMI effect in ribbon coated graphene by dispensing method. AFM observation confirmed a smoother ribbon surface by spin coating graphene. The very large enhancement of the GMI effect is a consequence of reducing the ribbon surface roughness and the closed magnetic flux path under the graphene thin film layer. This result provides a potential thinking for designing high sensitivity, lightweight and flexible GMI sensor with graphene-based materials.

Temperature Characteristics of a Fluxgate Current Sensor With Fe–Ni–Co Ring Core

In order to reduce the variations of sensitivity against temperature in practical fluxgate current sensors, we fabricated a fluxgate current sensor comprising a 20 $\mu \text{m}$ -thick Fe15Ni46Co39 film, which had not only low coercivity but also high Curie temperature, electroplated on a Cu ring. It was confirmed that the sensitivity of the sensor with Fe15Ni46Co39 core was the same as that of the sensor with the Fe21Ni79 core by adjusting the exciting current. The Fe–Ni–Co-core-based sensor demonstrated small sensitivity variations of $\sim 5$ % in a temperature range from −10 °C to 125 °C, whereas typical commercial sensors with a Co-based amorphous ribbon and a Fe–Ni-based sheet showed the sensitivity variations above 10%. The small fluctuation of sensitivity was considered to be attributed to the increase in the Curie temperature of the core material. It was clarified that the above-mentioned sensor consisted of Fe–Ni–Co core has high sensitivity together with high robustness against temperature.

Improved Performance of Integrated Solenoid Fluxgate Sensor Chip Using a Bilayer Co-Based Ribbon Core

In this paper, based on the multiwire core design and microelectromechanical system technology, we report improved performance of a microsolenoid fluxgate sensor by integrating a bilayer core of co-based amorphous ribbon. By means of utilizing integrated multilayer core structure and high permeability amorphous ribbon core material, this paper shows how a high-performance microfluxgate chip with small dimensions can be realized. The fabricated sensors exhibit a best sensitivity of 3165 V/T, a power of 183.2 mW and a linear range of 150 $\mu \text{T}$ at 100 kHz. The noise power density is found to be 0.5 nT/Hz $^{1/2}~1$ Hz and the noise rms level is 2 nT in the frequency range of 25 mHz–10 Hz.

Improved performance of the micro planar double-axis fluxgate sensors with different magnetic core materials and structures

As a classic weak magnetic field sensor, the fluxgate sensors have great potential application in many fields. This paper presents four kinds of the micro planar double-axis fluxgate sensors based on the MEMS technologies, which have different core materials and core structures. The core materials include electroplated permalloy, Co-based amorphous ribbon and Fe-based amorphous ribbon, and the core structures include single-layer open magnetic loop structure and double-layer closed magnetic loop structure. The sensor with closed double-layer Fe-based ribbon core exhibits a best sensitivity of 238 V/T due to reducing the magnetic flux leakage. The results show that the magnetic core with closed magnetic loop, high permeability and high saturation induction density will help increase the sensitivity of the micro double-axis fluxgate sensor.

Modulation of unidirectional anisotropy for Co-based amorphous ribbons by longitudinal pulse field

Field-induced unidirectional anisotropy of Co-based amorphous ribbons was discussed by magnetization measurement. The shifted hysteresis loops of Co58Fe5Ni10Si11B16 amorphous ribbons were obtained by annealing the samples in longitudinal magnetic field. Here, the feasibility of employing the longitudinal pulse field to tailor the anisotropy characteristic is demonstrated. It is found that the shifted loops can be technically controlled by enhancing the pulse field to modulate the magnetic anisotropy from unidirectional to uniaxial, and even back to unidirectional. The surface domains scan gives strong evidence that the pulse field can be one of the skillful methods to navigate the unidirectional anisotropy in the amorphous ribbons for potential applications.

A GMI biochip platform based on Co-based amorphous ribbon for the detection of magnetic Dynabeads

A giant magnetoimpedance (GMI) biochip platform for the low concentration detection of streptavidin-coupled magnetic Dynabeads of different sizes was successfully fabricated.

Study on the giant magnetoimpedance effect in micro-patterned Co-based amorphous ribbons with single strip structure and tortuous shape

Field-annealed Co-based commercial amorphous ribbons (Metglas® 2714A) with single strip structure and tortuous shape are fabricated by MEMS technology. The influence of the size, magnetic field and frequency on the giant magnetoimpedance (GMI) ratio of the ribbons with single strip structure and tortuous shape is investigated. The results show that the GMI ratio of micro-patterned Co-based amorphous ribbons with single strip structure increases with increasing in length and decreases with the increasing in width. The ribbons (length = 10 mm, width = 250 μm) with single strip can get higher GMI ratio at lower frequency (<40 MHz). The GMI ratio of micro-patterned tortuous-shaped Co-based amorphous ribbon with six turns is biggest with 82 %, obtained at a frequency of 40 MHz and a field of 20 Oe, and the GMI ratio increases with the increasing in turn number from two turns to six turns. All mechanisms (line width and tortuous shape) that influence the inductance and resistance will result in changes in the impedance and the GMI effect. The anisotropy field HK (15---20 Oe) of tortuous shape ribbon that the peak GMI ratio is larger than that (5---10 Oe) of the ribbon with single strip structure. The effect of the frequency on the GMI ratio of the ribbons with tortuous shape is more complex. This can be explanation by complex inductance of tortuous shape ribbons.

Detection of Dynabeads in small bias magnetic field by a micro fluxgate-based sensing system

The micro fluxgate sensors have shown high sensitivity for the magnetic beads detection. For portable magnetic biological detection, Co-based amorphous ribbons with high permeability and low saturation magnetic induction are chosen as core materials to lower the operation requirements of the fluxgate-based magnetic beads detection. The micro fluxgate sensors with single-layer core and bi-layer core are fabricated by Micro-Electro-Mechanical System technologies, which exhibit a power consumption of 10.88 mW and 24.48 mW, a sensitivity of 1644 V/T and 1456 V/T, and a noise of 1.66 nT/Hz1/2@1 Hz and 2.32 nT/Hz1/2@1 Hz, respectively. The Dynabeads with concentrations of 300 μg/ml in 10 μl are detected by the micro fluxgate-based sensing system based on static response, and the results show signal change ratio of 12.2% and 9.2% under the max signal difference at 215 μT and 480 μT of the bias magnetic field for two kinds of the sensors, respectively, which is near the saturation point of the sensors. The fluxgate-based bead detection system with Co-based ribbon core presents low demands for the bias magnetic field and power consumption.

Structural Characterization and Magnetoimpedance Effect of Current Annealed Co-Based Amorphous Ribbons at Different Ambient

The effect of current annealing in the air and vacuum on structure and magnetoimpedance (MI) response of Co68.15 Fe4.35 Si12.5 B15 amorphous ribbons was investigated. After 15 min of annealing, we found optimized currents where maximum MI ratio reached to 125 % and 160 % for annealing in the air and vacuum, respectively. Sample structures and their magnetic properties were investigated to explain the MI response after the annealing. Variation of MI responses can be correlated to the difference in the thermal conductivity of air and vacuum, field-induced anisotropy, and surface changes.

Spin precession by pulsed inductive magnetometry in thin amorphous plates

Broadband magnetic loss and damping behavior of Co-based amorphous ribbons and thin films have been investigated. The permeability and loss response of the transverse anisotropy ribbon samples in the frequency range DC to 1 GHz is interpreted in terms of combined and distinguishable contributions to the magnetization process by domain wall displacements and magnetization rotations. The latter alone are shown to survive at the highest frequencies, where the losses are calculated via coupled Maxwell and Landau–Lifshitz–Gilbert (LLG) equations. Remarkably high values of the LLG damping coefficient α = 0.1–0.2 are invoked in this theoretical prediction. Direct measurements of α by pulsed inductive microwave magnetometry are thus performed, both in these laminae and in amorphous films of identical composition, obtaining about one order of magnitude increase of the α value upon the 100 nm÷10 μm thickness range. This confirms that dissipation by eddy currents enters the LLG equation via large increase of the damping coefficient.

Simulation of Giant Magnetic Impedance (GMI) Effect in Co-based Amorphous Ribbons with Demagnetizing Field

Considering the role of demagnetizing field, based on linear Maxwell’s equations and the Landau-Lifshitz equation, the expressions of permeability and impedance were obtained using the improved theoretical model in this article. A numerical simulation was conducted using Matlab, and the results of calculations were well matched with the experimental results, indicating the importance of the demagnetizing field and that it should not be ignored. Utilizing the equivalence relation between the shape of the samples and the demagnetization factor which determined the value of the demagnetizing field, the influence of the aspect ratio of the samples on giant magnetic impedance (GMI) effect was researched. The calculations showed that the most significant GMI effect was obtained when the aspect ratio of samples was about 44. In addition, the optimal frequency to obtain the most significant GMI effect of the given sample was calculated. These researches may provide theoretical guidance for the development and use of a GMI sensor.

Effect of magnetic field annealing and size on the giant magnetoimpedance in micro-patterned Co-based ribbon with a meander structure

Micro-patterned Co-based amorphous ribbons (Metglas® 2714A) with a meander structure are fabricated by MEMS technology and the giant magnetoimpedance (GMI) effects are measured at different magnetic fields and frequencies. The effect of magnetic field annealing and size (line width and line length) on the GMI effect is investigated. It is found that the GMI effect in the transverse magnetic field-annealed state is larger than that in longitudinal magnetic field-annealed state and nonfield-annealed state. The maximum GMI effect increases from 82 % for the sample with 5 mm length to 150 % for the sample with 10 mm length, and the maximum GMI effect decreases with the increase of the line width.

High frequency magnetoimpedance response of stress annealed Co66.3Fe3.7Si12.0B18.0 amorphous alloy ribbons

Magnetoimpedance (MI) response of near-zero magnetostriction Co-based amorphous ribbons exhibiting a macroscopic uniaxial magnetic anisotropy induced by stress-annealing (300 MPa at 340, 360, and 400 °C during 1 h) is investigated in a frequency range from 10 MHz up to 1000 MHz. Comparison among MI effect of these stress-annealed ribbons with that previously reported in ribbons with similar composition in as-cast state is discussed. It is remarkable that a more spectacular and defined MI effect is observed in the stress-annealed ribbons owing to the presence of a macroscopic uniaxial transverse magnetic anisotropy developed with the stress annealing which enhances the transverse component of the magnetic susceptibility. The influence of a preceding stress relief before the stress-annealing process on the MI effect is also analyzed.

Magneto-Impedance Biosensor With Enhanced Sensitivity for Highly Sensitive Detection of Nanomag-D Beads

A magnetoimpedance (MI) biosensor based on Co-based amorphous ribbon was designed and tested to detect functionalized Nanomag-D magnetic beads. While previous studies were focused mainly on exploring the MI change for biosensing, we show that the sensitivity of the biosensor can be enhanced when the change in ac magnetoresistance (MR) or magnetoreactance (MX) is used. The frequency at which the sensitivity of the sensor is optimized can be tuned. This is of potential interest in developing functional biosensors with improved sensitivity and tunable frequency.

Computational modeling of GMI effect in Co-based amorphous ribbons

This paper presents a prediction of a giant magneto-impedance (GMI) effect on Co-based amorphous ribbons using an artificial neural network (ANN) approach based on a self-organizing feature map (SOFM). The input parameters included the compositions of Fe and Co, ribbon width and magnetizing frequency. The output parameter was the GMI effect. The results show that the proposed model can be used for estimation of the GMI effect in the amorphous ribbons.

Enhanced giant magneto-impedance effect in soft ferromagnetic amorphous ribbons with pulsed laser deposition of cobalt ferrite

We have grown a 50 nm thick magnetic layer of cobalt ferrite (CFO) on two Co-based amorphous ribbons of compositions Co65Fe4Ni2Si15B14 (type I) and Co69Fe4Ni1Mo2B12Si12 (type II) by a pulsed laser deposition technique. A comparative study of the influence of this CFO layer on the giant magneto-impedance (GMI) effect and field sensitivity (η) of the ribbons is presented. Our results reveal that the presence of the CFO layer enhanced both the GMI ratio and the field sensitivity of the ribbons. Relative to the plain ribbons, the GMI ratio and field sensitivity of the CFO-coated ribbons increased by 97% and 42% for type I and by 34% and 50% for type II, respectively. The enhanced effects are attributed to the modifications on the ribbon surface and closure of magnetic flux paths due to the CFO layer.