Giant Magnetoimpedance Curves Research Articles

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.

Preparation and magnetic properties of composite wire with double magnetic layers

Abstract In this study, C o 64 P 36 / N i 27 C o 59 P 14 /Cu composite wires with double magnetic layers are prepared by electroless deposition, and examined by hysteresis loop and giant magnetoimpedance (GMI). Hysteresis loops of the sample with double magnetic layers show a relatively obvious abrupt magnetization jump when compared a single-layer composite wire. The profile of GMI curves consists of a four-peak feature which indicates that both the magnetic layers have circumferential domain structure. The shift of the knee point on magnetization loops and the peak position on GMI curves show that dipolar interactions play a significant role between the two layers. The value of dipole field H d i decreases with the increase of frequency and thickness of the outer layer in this multi-layer sample by fitting the experimental data. All the results indicate an effective way to study the dipolar interactions among sophisticated composite magnetic wires.

Optimization of magnetoimpedance effect in Co-based ribbon by laser patterning for sensor arrays application

The giant magnetoimpedance (GMI) effect in Co-based ribbon with different patterning structures, named series structure (SS), parallel structure (PS) and cross structure (CS) with different angle, has been investigated. Absolute variation of impedance and GMI ratio (154% for sample SS, 220% for sample PS and 236% for sample CS at 5 MHz) in different patterning structures have been evaluated comprehensively. The double-peak GMI curves with a spindle-shape embossment are observed in sample PS and CS, which could be attributed to coupling effect between the strips and the especial geometry shape of samples. The enhancement of GMI effect in different patterning structures is attributed to different complex magnetic interaction. The results are beneficial for sensor arrays for measurement of weak magnetic fields.

The Disturbing Effect of the Stray Magnetic Fields on Magnetoimpedance Sensors.

The disturbing effect of the stray magnetic fields of Fe-based amorphous ribbons on the giant magnetoimpedance (GMI) sensor has been investigated systematically in this paper. Two simple methods were used for examining the disturbing effect of the stray magnetic fields of ribbons on the GMI sensor. In order to study the influence of the stray magnetic fields on the GMI effect, the square-shaped amorphous ribbons were tested in front, at the back, on the left and on the top of a meander-line GMI sensor made up of soft ferromagnetic films, respectively. Experimental results show that the presence of ribbons in front or at the back of GMI sensor shifts the GMI curve to a lower external magnetic field. On the contrary, the presence of ribbons on the left or on the top of the GMI sensor shifts the GMI curve to a higher external magnetic field, which is related to the coupling effect of the external magnetic field and the stray magnetic fields. The influence of the area and angle of ribbons on GMI was also studied in this work. The GMI sensor exhibits high linearity for detection of the stray magnetic fields, which has made it feasible to construct a sensitive magnetometer for detecting the typical stray magnetic fields of general soft ferromagnetic materials.

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.

Detection of the magnetite by giant magnetoimpedance sensor

Meander-line NiFe/Cu/NiFe films-based giant magnetoimpedance (GMI) sensor was employed to detect raw magnetite aiming to develop a sensitive magnetometer for the exploration of magnetite. The GMI effect was greatly decreased after placing the magnetite on the GMI sensing elements, which was probably related to the transverse magnetization process becoming strongly inhibited by the stray magnetic field. In addition, we observed an interesting phenomenon: the GMI curve on frequency dependency has shifted to a higher frequency when the magnetite was magnetized at the edge of the sensing elements. Significant changes in impedance can also be found when the magnetite was placed at the edge of GMI sensor without using the external magnetic field, demonstrating the possibility of using the GMI sensor for preliminary exploration of magnetic minerals.

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.

Enhanced Giant Magnetoimpedance Effect in Rapid Heat-Treated Fe-Based Amorphous Ribbons

An enhanced giant magnetoimpedance (GMI) effect of Fe-based amorphous ribbons is obtained by rapid heat treatment. The structural investigations on the ribbon reveal the presence of two phases, i.e. a fine grained Fe3Si phase and a residual amorphous phase on rapid heat treatment. The soft magnetic property is improved by rapid heat treatment; the crystal size and grain size of Fe3Si decrease. The maximum magnetoimpedance ratio obtained in the present study is 81% at 10 MHz, and the optimized heat-treated rate is 200°C/min. Separated GMI curves are observed after the simultaneous rapid heat treatment and magnetic field annealing. This suggests that tailoring of the nanocrystalline microstructures induced by optimum rapid heat treatment conditions can result in an excellent GMI effect.

Giant magnetoimpedance effect in stress-joule-heated Co-based amorphous ribbons

Co-based Co63Fe4B22.4Si5.6Nb5 amorphous ribbons with a width of 150 μm and a thickness of 50 μm were prepared by sin-gle-roller melt-spinning process. The giant magneto-impedance (GMI) effect of the stress-joule-heated ribbons under applied tensile stress ranging from 37 to 148 MPa was investigated. Experimental results show that the spectra of GMI ratio vs. exter-nal direct current (dc) field (Hex ) of the samples changes dramatically with annealing tension (？) and driving frequency. The single-peak (SP) GMI curve with maximum GMI ratio of 260% and magnetic field sensitivity of 52%/Oe was obtained in the sample applied tensile stress of 74 MPa at frequency of 3.6 MHz. A three-peak behaviour appeared in the samples under σof 111 and 148 MPa. The uncommon three-peak behaviour was attributedto several factors, which effectively originated from the balance between domain-wall movement and magnetization rotation.

Improvement in Giant Magnetoimpedance by High Ion Dose

The effects of annealing and ion-irradiation on the magnetic properties of amorphous Co66Fe4B15Si15 alloys have been investigated by means of the changes of the giant magnetoimpedance (GMI). In general, there are differences in magnitude and shape of the GMI curves between as-quenched amorphous and ion-irradiated samples. The results indicate that the effects of ion irradiation on the magnetic properties of the as-quenched sample are quite large and show the dependence for ion dose. But a drastic decrease and ion-dose dependence, caused by ion-irradiation, is observed in the magnitude of the GMI of the sample annealed at 380°C, which has a maximum value of the GMI due to the presence of ultra-soft magnetic materials.

Effects of Gamma Irradiation and Thermal Annealing on the Co-Based Amorphous Ribbon

The effects of annealing and gamma irradiation on the magnetic properties of amorphous Co66Fe4B15Si15 alloys have been investigated by means of the changes in the giant magneto-impedance (GMI). The results show that there are no differences in the shape of the GMI curves for the samples which are as-quenched, annealed, gamma irradiated, and gamma irradiated after annealing. The GMI ratio showed drastic change according to the sample histories, the GMI ratio drastically increased in the annealed sample compared to as-quenched state, and this increase was recovered considerably by gamma irradiation, but no changes were observed in the as-quenched samples by gamma irradiation. These changes of GMI ratio with sample histories explained in terms of magnetic softness and the fluctuation of the circumferential/transverse anisotropy by gamma heating.

High sensitivity giant magnetoimpedance (GMI) magnetic transducer: magnitude versus phase sensing

This paper presents the results of investigations recently done by our research group that lead to a new and much better approach to the design of GMI (giant magnetoimpedance) magnetic transducers, which considers the changes in the impedance phase characteristics of GMI sensors due to varying low-intensity magnetic fields, instead of the usual impedance magnitude characteristics considered in the GMI literature. The development process of this new class of magnetic field transducers is discussed, beginning with the definition of the ideal conditioning of the GMI sensor elements (the dc level and frequency of the excitation current and the sample length), proceeding to compare the differences observed between the impedance magnitude and phase of GMI sensors and closing with the electronic circuits that condition ribbon-shaped GMI sensors and read their phase or magnitude variation as a function of the longitudinal magnetic field. Simulation studies, including the full electronic circuit and based on the experimental data obtained from measured GMI curves, have shown that an improvement in the sensitivity of GMI magnetometers larger than ten times can be expected when phase-based transducers are used instead of magnitude-based transducers. Finally, it is also shown that phase-based transducers are highly adequate for miniaturization purposes.

Development of ultra‐thin glass‐coated amorphous microwires for HF magnetic sensor applications

AbstractIn this paper we report novel results on magnetic properties and giant magnetoimpedance (GMI) effect at frequencies between 10 MHz and 500 MHz in ultra‐thin Co–Fe‐rich amorphous glass‐coated microwires with near‐zero magnetostriction constant and with metallic nucleus diameter ranging between 5 μm and 22 μm. Co67.05Fe3.84Ni1.44Si14.47B11.51Mo1.69 glass‐coated amorphous microwires with metallic nucleus diameter ranging between 5 μm and 22 μm and total diameter between 10 μm and 23 μm with vanishing magnetostriction constant of the order of –(1–3) × 10–7 fabricated by the Taylor–Ulitovsky method were studied. Most of the samples studied exhibited excellent soft magnetic behaviour and a large GMI effect. Off‐diagonal components, real and imaginary parts of the GMI were analysed. Even in the thicker samples (metallic nucleus 22 μm) the penetration skin depth calculated from the GMI curves at 30 MHz was about 1 μm. Therefore the surface magnetization process and surface defects are of special importance to achieve good HF properties in these wires. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of Fe doping and FeNi-layer thickness on the magnetic properties and GMI effect of electrodeposited Ni100−xFex/Cu (x = 0–95) wires

A systematic study has been performed by the influence of Fe doping and FeNi-layer thickness on the giant magnetoimpedance (GMI) effect of electrodeposited Ni100−xFex/Cu (x = 0–95) composite wires. Results obtained show that there is a correlation between the structure, soft magnetic properties and the GMI effect. Among the compositions investigated, the largest MI ratio is achieved for Ni44Fe56/Cu as a result of it having the softest magnetic property (i.e. the lowest coercivity), which arises from the smallest nanograin size. As the NiFe-layer thickness (t) increases from 1 to 27.4 µm, the GMI ratio initially increases, reaches a maximum of 110% at t = 27.4 µm and then decreases for t > 27.4 µm. Interestingly, GMI curves show a single-peak feature for wires with t < 20 µm, but a double-peak one for wires with t ⩾ 20 µm. This indicates that there is a formation of a circular domain structure with a well-defined circumferential anisotropy in the NiFe magnetic layer of the wires with t ⩾ 20 µm. This in turn results in a great improvement in the GMI effect of these wires.

Giant magnetoimpedance of electrodeposited Co/Cu/Co on Ag wires

Giant magnetoimpedance (GMI) was studied in electrodeposited Co/Cu/Co-coated Ag wires with variations in the axial dc magnetic field (0–2 kOe), frequency of ac driving current (1 kHz–100 MHz), thickness of each layer (1.0–25.0 µm) and diameter of the Ag core (47.7 and 120.0 µm). With increasing thickness of coated layers and Ag cores, the maximum GMI ratio increased but the characteristic frequency decreased. Unlike Co-coated Ag wires, the frequency-dependent GMI curves of these multilayered wires were broadened and asymmetric. The GMI behaviours were explained in terms of the distribution of current density and current flow in the coated wires obtained from the finite element method simulation program.

Three-peak behavior in giant magnetoimpedance effect in Fe 73.5−xCr xNb 3Cu 1Si 13.5B 9 amorphous ribbons

A systematic study of the giant magnetoimpedance (GMI) effect in Fe 73.5− x Cr x Nb 3Cu 1Si 13.5B 9 amorphous ribbons with x=0, 2, 4, 6, 8 and 10 is presented. The complex impedance in these compounds was measured for applied fields from −80 to 80 Oe at room temperature, via the so-called four-probe technique. Depending on the frequency, the experimentally observed GMI curves usually exhibit two types of behavior, namely single-peak (SP), and two-peak (TP). In this work, we emphasize the presence of a “ three-peak behavior” in GMI curves. It occurs between SP and TP behaviors. The mechanisms leading to the three-peak behavior are discussed.

Giant magnetoimpedance effect in a glass-coated microwire LC-resonator for high-frequency sensitive magnetic sensor applications

This letter reports on the high-frequency giant magnetoimpedance (GMI) effect in a LC-resonator built on a glass-coated Co 83.2B 3.3Si 5.9Mn 7.6 microwire with two cylindrical electrodes at the ends of the microwire. In the investigated frequency range of 100–1000 MHz, the shape of GMI curves varies drastically as the frequency increases. It has been demonstrated that the resonance in a glass-coated microwire LC-resonator occurs at a specific intensity of the applied dc magnetic field. The sudden changes of the phase angle as large as 180° evidence the occurrence of the resonance. The GMI features in a LC-resonator originate from both the permeability changes of the microwire and the LC-resonance of the circuit. More interestingly, extremely large increases of GMI in the vicinity region of the resonant frequency (∼890 MHz) are also observed. The maximum GMI response up to 10,000% has been found at the frequency of 889.41 MHz. This result is very beneficial for developing a new family of high-frequency and ultra-sensitive GMI-based magnetic sensor applications.

Dipolar-biased giant magnetoimpedance

The effect of the dipolar field on the magnetoimpedance in Fe- and Co-based wires is presented. In the experiments a Co-based wire was used as a probe to measure the giant magnetoimpedance (GMI), while a Fe-based wire was employed to generate the dipolar field. The GMI curve showed a shift in the anisotropy field and a highly asymmetric profile. The dipole–dipole interaction can be employed to design novel linear GMI sensors and to properly tune their field operation.

Giant magnetoimpedance in FeAg granular alloys

We have observed giant magnetoimpedance (GMI) in an FeAg granular alloy. Impedance and transverse susceptibility (TS) measurements as a function of the external dc magnetic field were made at room temperature. The variation of the magnetoimpedance ratio with magnetic field has been related to a corresponding TS ratio change as a function of the magnetic field. The peaks in the GMI and TS curves are in the same position and have been associated in both cases to effective anisotropy fields.

Asymmetric giant magnetoimpedance curve due to antiferromagnetic coupling

The asymmetric giant magnetoimpedance curves have been measured under the rotation of magnetic field on the weak-field annealed Co-based amorphous ribbons to analyze the characteristics of bias field. The bias field from the hard magnetic phases is expected to be of an order of 100 Oe along the annealing field direction. The effective field of soft magnetic phase in the field region parallel to the bias field is less than that antiparallel to the bias field, indicating that an antiferromagnetic exchange coupling exists between the magnetization of the soft phase and the bias field of the hard magnetic phases.