Giant Magnetoimpedance Research Articles

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.

Engineering of magnetic properties and magnetoimpedance effect in Fe-rich microwires by reversible and irreversible stress-annealing anisotropy

Herein, by using both hysteresis loops and the Giant magnetoimpedance, GMI, measurements, the magnetic properties of amorphous FeSiBC microwires have been thoroughly analyzed paying attention on the influence of annealing (under stress or without stress) on the GMI effect and magnetic properties of Fe–Si–B–C microwires. We observed that stress annealing allows the induction of transverse magnetic anisotropy and the GMI effect improvement. This stress-annealing induced anisotropy depends on the stress-annealing conditions: annealing time and stress applied during the annealing and can be partially annealed out by subsequent furnace annealing. However, the reversibility of the stress-annealing induced anisotropy depends on the stress-annealing conditions. Particularly, most of the transverse induced magnetic anisotropy obtained by stress-annealing at high stresses values is irreversible. Stress-annealing followed by annealing without stress allows further improvement of the GMI effect in Fe–Si–B–C microwires in a wide frequency range.Coercivity, remanent magnetization, and magnetoimpedance ratio of FeSiBC microwires can be tuned by annealing conditions: annealing time and stress.All studied microwires present GMI hysteresis. The sample with the highest GMI ratio presents the lowest GMI hysteresis.Observed experimental results are discussed considering relaxation of internal stresses, compressive “back-stresses” arising after stress annealing and topological short range ordering.

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.

Giant magnetoreactance in magnetic nanowires

We outline the idea of magnetic-field sensing with a nanometer spatial resolution using the effect of giant magnetoreactance (GMX) and we discuss results of our micromagnetic studies of domain-wall-assisted (or double-vortex-assisted) GMX in nanomagnets. By analogy to low-frequency giant magnetoimpedance (GMI), we consider systems of domains magnetized perpendicular to the direction of the AC current that creates an alternating Oersted field, thus, it drives the DW oscillations. Because of small cross-sections, the nanomagnets are not capable to induce large changes of the magnetic flux, therefore, the impedance of magnet-containing nanocircuits is dominated by the static resistivity (in accessible frequency regimes), while, GMX is an alternative effect to be utilized for sensing. We analyze in detail the effect in single-crystalline nanowire of cobalt with the easy axis transverse to the nanowire axis. In that system, small coherent shifts of the domain walls (DWs) induce relatively high changes of the magnetic flux through the largest cross-section of the nanowire due to large density of periodically packed DWs. Driven by the alternating transverse field of the Oersted origin, the system allows for perpendicular (the field directed perpendicular to the long axis of the nanowire and to the domain magnetization) GMX of improved characteristics (the GMX ratio and the field sensitivity of GMX) at a high stability of the magnetic structure in a wide region of the external field. Moreover, due to a non-zero overall magnetization (created by DWs), the perpendicular GMX is strongly asymmetric with respect to the field reversal (in a low-field regime). Also, we study the transverse GMX (the field parallel to the domain magnetization).

Design, implementation and experimental characterisation of a high sensitivity GMI gradiometer with an interference compensation system

The giant magneto-impedance (GMI) effect has been, since its discovery, one of the most promising technologies in the development of magnetic sensors. Features such as high sensitivity, stability and low cost are the main reasons for the development of this type of magnetometers. This study reports the design, implementation and experimental characterisation of a high sensitivity GMI gradiometer, aimed at measuring low-intensity magnetic fields. A first-order gradiometer was designed, based on the impedance phase characteristics of two Co 70 Fe 5 Si 15 B 10 amorphous ribbon-shaped sensors connected to an electronic circuit that converts the magnetic field into an output voltage. The developed prototype can operate not only as gradiometer but also as two separate magnetometers, which allows it to incorporate a compensation system against deviations in the biasing field of the GMI sensors. The experimental results for the gradiometer showed a sensitivity of 99 mV/μT, a measuring range of ±30 μT, a magnetic noise of 5 nT Hz -1/2 at 5 Hz and a resolution of 40 nT within a 500 Hz bandwidth. The compensation system has shown a settling time of 1.6 s for perturbations in the range ±10 μT with a steady-state error <;0.02%. All experiments were performed in an unshielded environment.

Giant magneto impedance effect of Co-rich amorphous fibers under magnetic interaction

The quasi-metallic fibers were selected from 1 to 40 pieces and connected in parallel in this study. The giant magneto impedance (GMI) effect of Co-based melt extract fibers in the bundle mode was investigated, and the distribution of the surface circumferential magnetic field on the fibers was also analyzed. Such distribution was induced by the driving current, which gave rise to the circular magnetization process and the GMI effect. The improved GMI effect with much higher field sensitivity was observed in these fiber bundles. Results show that the field sensitivities of the four-fiber and six-fiber bundles reach 19.5 V·m·kA−1 (at 1 MHz) and 30.8 V·m·kA−1 (at 5 MHz). The circumferential magnetic field distributed throughout the fiber’s circumferential surface is rearranged and becomes uneven due to the magnetic interaction among fibers. There are both strengthened and weakened magnetic field parts around these fibers’ surfaces. The strengthened magnetic field improves the circumferential domain magnetization of the surface, resulting in larger GMI effects. However, the weakened parts inhibit the circumferential magnetization process and, therefore, the GMI effect. This also induces greater magnetization damp because of the increased domain interactions under the strong skin effect. The co-effect between the magnetic domains and the circumferential magnetization induces the optimization of the GMI effect in the four-fiber bundles. The observed GMI effect proves that fibers in bundle form can modify the sensitivity of the GMI effect. Moreover, different fiber bundles could be tuned according to the working conditions in order to manipulate the GMI response.

Enhanced dc Magnetic Field Sensitivity for Coupled ac Magnetic Field and Stress Driven Soft Magnetic Laminate Heterostructure

To improve the dc magnetic field sensitivity of conventional inductor-type (i.e., longitudinally driven giant magnetoimpedance) sensor at the low excitation frequency, a transformer-type laminated magnetic sensor consisting of soft magnetostrictive alloy FeBSiC/piezoelectric ceramics Pb(Zr,Ti)O3/FeBSiC heterostructure wrapped with both the exciting and sensing coils (i.e., FPFCexCse) is proposed. Compared to the inductor-type dc magnetic sensor (i.e., Hac driven FeBSiC ribbons with only exciting coils), on one hand the ac magnetic field (Hac) produced by the exciting coil and the stress produced by electrically driven PZT are synchronously coupled to enhance the magnetic induction variation of FeBSiC and the induced voltage sensitivity of sensing coils. On the other hand the mutual inductance induced voltage eliminates the weak skin effect at the low excitation frequency. When the exciting coil and PZT of FPFCexCse laminate are synchronously excited with 5 mA ac current and 5 V voltage at the mechanical resonance frequency, the maximum magnetic field sensitivity of 21200 V/T is achieved. This is about 4.08 times and 2.98 times as high as that of FeBSiC ribbon with only exciting coils (5190 V/T) and FeBSiC ribbons with both exciting and sensing coils (7120 V/T), respectively. Furthermore the equivalent magnetic noise of $114~{\mathrm {pT}}/\sqrt {{\mathrm {Hz}}} $ (at 1Hz) is achieved by the FPFC exCse laminate, which is obviously lower than that of Hac driven FeBSiC ribbons.

The development of a micro-coil-on-ASIC type GSR sensor driven by GHz pulse current

Through applying GHz (Gigahertz) pulse current on the amorphous micro wire, we observed an increase in the coil voltage around the wire, and a sine function relationship between the coil voltage and the surrounding magnetic field. We assumed that the new performance of the coil voltage must be caused by the rotation of electron spins on the wire surface with GHz angular velocity, induced by the magnetic field force in the same direction, and proposed to name the observed new phenomena as GSR (Gigahertz Spin Rotation) effect. The developed GSR sensor presents excellent features with enhanced sensitivity and low hysteresis better than that of the GMI (Giant Magnetoimpedance) sensor.We developed the production technology to produce micro coils and developed a Micro-coil-on-ASIC (Application Specified Integrated Circuit) type GSR sensor, where the micro coils are directly formed on the ASIC surface, making small size GSR sensor possible.

Reversible and Non-Reversible Transformation of Magnetic Structure in Amorphous Microwires

We provide an overview of the tools directed to reversible and irreversible transformations of the magnetic structure of glass-covered microwires. The irreversible tools are the selection of the chemical composition, geometric ratio, and the stress-annealing. For reversible tuning we use the combination of magnetic fields and mechanical stresses. The studies were focused on the giant magnetoimpedance effect and the velocity of the domain walls propagation important for the technological applications. The essential increase of the giant magnetoimpedance effect and the control of the domain wall velocity were achieved as a result of the use of two types of control tools. The performed simulations reflect the real transformation of the helical domain structures experimentally found.

Magnetic Sensor Based on Giant Magneto-Impedance in Commercial Inductors

Magnetic sensors have various applications in navigation, power distribution, robotics, factory automation, and medical diagnosis. The development of highly sensitive magnetic sensors usually requires complicated and costly fabrication process. Herein, we report giant magneto-impedance of 41036% in the commercially available ferrite core inductors. A magnetic field detection limit of 10 nT at 1 Hz has been obtained by directly measuring the impedance of the as-obtained inductor without any optimization. With a 100 pF capacitor in series connection with the inductor where lower impedance facilitates the measurement process, a limit of detection of 625 pT at 1 Hz has been obtained in the series <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> resonator. These results can be understood in terms of the magnetic field-dependent self-resonance in the inductors which act as lumped <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> resonators. Compared with the traditional electromagnetic induction sensing mode, the magneto-impedance sensing mode shows 5000 folds improvement in the magnetic field detection capability.

Magnetic properties and giant magnetoimpedance effect of FINEMET/Fe50Pt50 composite ribbons

In order to study the magnetic properties and giant magnetoimpedance (GMI) effect of FINEMET/Fe50Pt50 composite ribbons. A series of Fe50Pt50 films with different thickness (t) were deposited onto FINEMET ribbons by magnetron sputtering. The results showed that all FINEMET/Fe50Pt50 composite samples maintain good soft magnetic properties. The anisotropy field decreases firstly and then increases with the increasing of Fe50Pt50 layer thickness (0 ~ 117 nm). When the coating thickness is 98 nm, FINEMET/Fe50Pt50 composite samples obtain the smallest coercivity field (0.04 Oe). Its GMI ratio is 122%, which is three times higher than the FINEMET ribbon itself. This clearly indicates that addition of the Fe50Pt50 layer can impact magnetic properties and significantly enhance the GMI ratio, which is analyzed in terms of exchange coupling and dipole interaction between the FINEMET ribbon and coating film. We believe that these results provide a good guidance for GMI effect of soft magnetic amorphous composite materials with high sensitivity magnetic sensors.

Effect of Coating and Annealing on Giant Magneto Impedance in Co and Fe-Based Amorphous Wires

Effect of coating with different chemical complexes on giant magneto impedance effect (GMI) was experimentally investigated in Fe and Co-based amorphous wires. The successive ionic layer adsorption and reaction (SILAR) technique was used for coating of the samples at room temperature. The SILAR method mainly based on adsorption and reaction on the ions from the solution and rinsing. Co and Fe-based amorphous wires were coated with CoO, asphaltene and ZnO chemical complexes. The coating thickness was determined to be about 1 μm thick. Maximum GMI ratio for Co and Fe-based samples were measured at 4 MHz and 5 MHz frequency, respectively. Influence of annealing at different temperatures on GMI effect was also experimentally investigated in the same samples. The coated samples were annealed at 300 C, 400 C, 500 C and 600 C temperatures in order to stress relief for 30 minutes. It is observed that the GMI ratio on Co- and Fe-based ZnO coated samples was highest at 500 ºC, while it was maximum on CoO coated Co-based samples at 400 ºC and on CoO coated Fe-based samples at 500 ºC. The highest GMI ratio among the measured samples was detected as 216 on the Fe-based, ZnO coated and annealed sample at 500 ºC at 5 MHz, while the smallest GMI ratio, was found to be as 88 on Co-based as-cast sample at 4 MHz. The measurements show that the GMI ratio is a combined effect of coating, annealing and frequency of ac current in a static magnetic field. Keywords Amorphous magnetic materials, SILAR technique, giant magneto impedance. Special Issue of Educational Sciences DOI: 10.7176/JSTR/6-06-03

Stress-induced magnetic anisotropy enabling engineering of magnetic softness of Fe-rich amorphous microwires

Stress-annealing allows considerably modify magnetic properties of Fe-rich glass-coated microwires. Varying the stress-annealing conditions (temperature, time and stress applied during the annealing) we can observe either remarkable improvement of magnetic softness and giant magnetoimpedance (GMI) effect. Observed changes have been attributed to the transverse magnetic anisotropy. An improvement of the circumferential permeability in the surface layer of metallic nucleus is evidenced from observed magnetic softening and remarkable GMI effect rising. We assumed that stress-annealing leads to an increase in the outer domain sheath with transverse magnetic anisotropy rise in expense of inner axially magnetized core typically existing in as-prepared Fe-rich microwires. Consequently, stress annealing enabled us to design the magnetic anisotropy distribution beneficial for optimization of the GMI effect and magnetic softness of Fe-rich magnetic microwires.

Ultrafast Magnetization Dynamics in Metallic Amorphous Ribbons with a Giant Magnetoimpedance Response

We report on the dynamics of laser-induced magnetization in magnetic ribbons using the time-resolved magneto-optical Kerr effect. Damped oscillations representing precessional motion of the magnetization vector are observed in a $\mathrm{Co}$-rich ribbon. The frequency and amplitude of these oscillations depend on the fluence of the pump laser pulse and the external magnetic field. With an anisotropy factor defined by the effective field of the magnetic anisotropy, we demonstrate that the frequency of the ferromagnetic mode activated by the laser pulses is close to the frequency of the giant magnetoimpedance response. These findings provide an opportunity to investigate the magnetoimpedance effect in the gigahertz frequency range using ultrashort laser pulses and are particularly interesting for the development of broadband sensor devices. Furthermore, our results link laser-induced magnetization dynamics with magnetoresistive sensing techniques, thus opening up the supergigahertz domain to magnetoimpedance studies.

Stress-Induced Magnetic Anisotropy Enabling Engineering of Magnetic Softness GMI Effect and Domain Wall Dynamics of Amorphous Microwires

Abstract—We showed that stress-annealing performed under proper conditions can improve magnetic softness, domain wall (DW) velocity and giant magneto-impedance (GMI) effect of Fe-based microwires. One order of magnitude improvement of GMI ratio and more than 100% increase of DW velocity have been achieved by stress-annealing. Observed dependencies have been related to the domain structure modification evidenced from the evolution of the hysteresis loops upon stress-annealing. We discussed observed results considering that the outer domain shell with transverse magnetic anisotropy affects the travelling DW in a similar way as the application of transverse bias magnetic field. GMI ratio improvement is attributed to beneficial magnetic anisotropy distribution achieved by stress-annealing.

A Combination of a Vibrational Electromagnetic Energy Harvester and a Giant Magnetoimpedance (GMI) Sensor.

An energy harvesting device combined with a giant magnetoimpedance (GMI) sensor is presented to analyze low frequency vibrating systems. An electromagnetic harvester based on magnetic levitation is proposed for the electric power generation. The device is composed of two fixed permanent magnets at both ends of a cylindrical frame, a levitating magnet acting as inertial mass and a pick-up coil to collect the induced electromotive force. At the resonance frequency (10 Hz) a maximum electrical power of 1.4 mW at 0.5 g is generated. Moreover, an amorphous wire was employed as sensor nucleus for the design of a linear accelerometer prototype. The sensor is based on the GMI effect where the impedance changes occur as a consequence of the variations of the effective magnetic field due to an oscillating magnetic element. As a result of the magnet’s periodic motion, an amplitude modulated signal (AM) was obtained, its amplitude being proportional to mechanical vibration amplitude (or acceleration). The sensor’s response was examined for a simple ferrite magnet under vibration and compared with that obtained for the vibrational energy harvester. As a result of the small amplitudes of vibration, a linear sensor response was obtained that could be employed in the design of low cost and simple accelerometers.

Impact of uniaxial stress on soft-magnetic and magneto-impedance properties of vitrified magnetostrictive microwires

Abstract The investigation addresses the impact of stress on soft magnetic and giant magneto-impedance (GMI) of rapidly quenched Fe77.5Si7.5B15, (Co94Fe6)72.5Si12.5B15 and (Co94Fe6)72.5Si12.5B12.5Nb0.5Cr2 microwires. Differential scanning calorimetry revealed interesting phase stability in the later alloys. The vitrified microwires contained dominant Co and a lean Fe content showed much superior soft magnetic properties and high magnetoimpedance. The alloy microwires incorporated with Nb and Cr manifested lowest coercivity value of 0.034 Oe with a high GMImax value of 425% in the as-quenched state. The uniaxial stress applied on the microwires modified the shape of the hysteresis loops and GMI plots. The hysteresis loops showed stress dependence of coercivity based on alloy chemistry, phase stability and consequent magnetostriction. The GMImax revealed sensitive change with respect to the applied stress in all the alloy microwires. In addition to GMImax interesting features were observed in the GMI profile pertaining influence of stress on the anisotropy field. The anisotropy field shifted systematically in one of the alloy microwires which displayed symmetric dual GMI peaks. The stress was also found to modify the asymmetric characteristics in a microwire.

Ultrasensitive Magnetic Field Sensors for Biomedical Applications.

The development of magnetic field sensors for biomedical applications primarily focuses on equivalent magnetic noise reduction or overall design improvement in order to make them smaller and cheaper while keeping the required values of a limit of detection. One of the cutting-edge topics today is the use of magnetic field sensors for applications such as magnetocardiography, magnetotomography, magnetomyography, magnetoneurography, or their application in point-of-care devices. This introductory review focuses on modern magnetic field sensors suitable for biomedicine applications from a physical point of view and provides an overview of recent studies in this field. Types of magnetic field sensors include direct current superconducting quantum interference devices, search coil, fluxgate, magnetoelectric, giant magneto-impedance, anisotropic/giant/tunneling magnetoresistance, optically pumped, cavity optomechanical, Hall effect, magnetoelastic, spin wave interferometry, and those based on the behavior of nitrogen-vacancy centers in the atomic lattice of diamond.

Optimization of magnetic properties and GMI effect of Thin Co-rich Microwires for GMI Microsensors.

Magnetic microwires can present excellent soft magnetic properties and a giant magnetoimpedance effect. In this paper, we present our last results on the effect of postprocessing allowing optimization of the magnetoimpedance effect in Co-rich microwires suitable for magnetic microsensor applications. Giant magnetoimpedance effect improvement was achieved either by annealing or stress-annealing. Annealed Co-rich presents rectangular hysteresis loops. However, an improvement in magnetoimpedance ratio is observed at fairly high annealing temperatures over a wide frequency range. Application of stress during annealing at moderate values of annealing temperatures and stress allows for a remarkable decrease in coercivity and increase in squareness ratio and further giant magnetoimpedance effect improvement. Stress-annealing, carried out at sufficiently high temperatures and/or stress allowed induction of transverse magnetic anisotropy, as well as magnetoimpedance effect improvement. Enhanced magnetoimpedance ratio values for annealed and stress-annealed samples and frequency dependence of the magnetoimpedance are discussed in terms of the radial distribution of the magnetic anisotropy. Accordingly, we demonstrated that the giant magnetoimpedance effect of Co-rich microwires can be tailored by controlling the magnetic anisotropy of Co-rich microwires, using appropriate thermal treatment.

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”.