Giant Magnetoimpedance Effect Research Articles

Giant magneto-impedance effect in amorphous CoP@Cu microstrip based device in a wide frequency range

The giant magneto-impedance effect (GMI) consists in a large variation in the electrical impedance that occurs in some magnetic materials when subjected to a variable external magnetic field. Here we present an experimental study of the GMI in a wide frequency range observed in a structure of the metallic amorphous magnetic alloy CoP electrodeposited on copper microwires by using a microstrip configuration. In the low frequency range, the magnetic field dependence of the impedance is due to the behavior of the circumferential ac susceptibility in the magnetic coating. In the microwave range the behavior of the GMI is dominated by the main dynamical magnetic phenomenon at high frequencies, namely ferromagnetic resonance (FMR). The experimental data are well fit by Kittel equation for the FMR frequency for a ferromagnetic layer with a saturation magnetization similar to the ones reported in previous works. The structural stability of the CoP alloy against aging effects was also investigated. The overall results indicate that the CoP alloy is a good candidate for applications in sensors and in microwave devices.

Line spacing effect on the giant magnetoimpedance behavior on microribbon with meander type: a comparison of theory and experiment

Purpose Microribbon with meander type based on giant magnetoimpedance (GMI) effect has become a research hot spot due to their higher sensitivity and spatial resolution. The purpose of this paper is to further optimize the line spacing to improve the performance of meanders for sensor application. Design/methodology/approach The model of GMI effect of microribbon with meander type is established. The effect of line spacing (Ls) on GMI behavior in meanders is analyzed systematically. Findings Comparison of theory and experiment indicates that decreasing the line spacing increases the negative mutual inductance and a consequent increase in the GMI effect. The maximum value of the GMI ratio increases from 69% to 91.8% (simulation results) and 16.9% to 51.4% (experimental results) when the line spacing is reduced from 400 to 50 µm. The contribution of line spacing versus line width to the GMI ratio of microribbon with meander type was contrasted. This behavior of the GMI ratio is dominated by the overall negative contribution of the mutual inductance. Originality/value This paper explores the effect of line spacing on the GMI ratio of meander type by comparing the simulation results with the experimental results. The superior line spacing is found in the identical sensing area. The findings will contribute to the design of high-performance micropatterned ribbon with meander-type GMI sensors and the establishment of a ribbon-based magnetic-sensitive biosensing system.

Giant magnetoimpedance effect and spin accumulation in conjugated polymeric networks with inhomogeneity

The magnetoimpedance effect allows us to estimate the extent of spin dependent scattering in disordered solids. The change in impedance with respect to applied magnetic field manifests through local change in permeability on the surface and it amplifies at defect sites. The local electrical inhomogeneities are expected to aid this effect through spin dependent scattering. The organic conjugated electrical networks provide scope for producing such inhomogeneities formed by path defects and protonic charge accumulation leading to spin dependent scattering. This hypothesis is investigated in the present work taking polyaniline as a prototype network. The electrical inhomogeneities in the network were controlled by selective oxidation and aging in polyaniline. The Giant Magnetoimpedance (GMI) was observed in the electrically inhomogeneous network with the change in electrical impedance of the order of 50%–60% for lower frequencies with prominent capacitive coupling and a change of the order of 200% at higher frequencies with prominent inductive coupling with the application of magnetic field. However, no spin accumulation was observed in the insulating networks formed by a modified oxidative process. This study is expected to serve as a tool to develop frequency selective spin accumulation based magnetic field sensors and oscillator networks.

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.

Non-Contact Current Sensing System Based on the Giant Magnetoimpedance Effect of CoFeNiSiB Amorphous Ribbon Meanders.

A sensitive non-contact sensing system based on the CoFeNiSiB amorphous ribbon giant magnetoimpedance (GMI) effect is proposed for current testing. The sensing system consists of a GMI probe, a sinusoidal current generator, a voltage follower, a preamplifier, a low-pass filter, and a peak detector. Four different GMI probes derived from amorphous ribbon meanders are designed and fabricated through MEMS processes. GMI probes were driven by a 10 MHz, 5 mA AC current. A permanent magnet was used to provide a bias magnetic field for the probe. The effect of the bias magnetic field on the output DC voltage was investigated. This non-contact current sensing system exhibits good sensitivity and linearity at a bias magnetic field Hbias = 15 Oe. The sensitivity can reach up to 24.2 mV/A in the ±1.5 A range.

Rotation angle detection based on low-frequency giant magnetoimpedance effect

Rotation angle detection based on low-frequency giant magnetoimpedance effect

Wearable Magnetic Field Sensor with Low Detection Limit and Wide Operation Range for Electronic Skin Applications.

Flexible electronic devices extended abilities of humans to perceive their environment conveniently and comfortably. Among them, flexible magnetic field sensors are crucial to detect changes in the external magnetic field. State-of-the-art flexible magnetoelectronics do not exhibit low detection limit and large working range simultaneously, which limits their application potential. Herein, a flexible magnetic field sensor possessing a low detection limit of 22 nT and wide sensing range from 22 nT up to 400 mT is reported. With the detection range of seven orders of magnitude in magnetic field sensor constitutes at least one order of magnitude improvement over current flexible magnetic field sensor technologies. The sensor is designed as a cantilever beam structure accommodating a flexible permanent magnetic composite and an amorphous magnetic wire enabling sensitivity to low magnetic fields. To detect high fields, the anisotropy of the giant magnetoimpedance effect of amorphous magnetic wires to the magnetic field direction is explored. Benefiting from mechanical flexibility of sensor and its broad detection range, its application potential for smart wearables targeting geomagnetic navigation, touchless interactivity, rehabilitation appliances, and safety interfaces providing warnings of exposure to high magnetic fields are explored.

Effects of drawing and tension stress annealing on the structure and magnetic properties of Co-based amorphous wire

Cold drawing significantly improves the size uniformity of the amorphous wire, but leads to wire curling. Tensile stress annealing (TSA) is the key to regulating the straightness and magnetic properties of Co-based amorphous wires, but their intrinsic correlation is still unclear. Herein, the effects of TSA on the morphology, microstructure, soft magnetic properties and longitudinal driven giant magneto-impedance (LD-GMI) effect of cold drawn Co-based amorphous wires have been studied in detail. It was found that increasing tensile stress can effectively straighten the drawn amorphous wire, yet at the cost of decreasing fracture strength, increasing coercivity and deteriorating GMI effect. Furthermore, appropriate annealing can restore the magnetic properties of the TSA amorphous wire. The variation of magnetic properties is relative to the change of circular anisotropic field and magnetic domain structure.

Magnetic Properties and Applications of Glass-coated Ferromagnetic Microwires

A remarkable magnetic softness and giant magnetoimpedance (GMI) effect at GHz frequency range havebeen observed in glass-coated microwires subjected to appropriate postprocessing. Co-based microwires present higher GMI effect. Insulating and flexible glass-coating allows use of magnetically soft amorphous glass-coated microwires for stresses or temperature monitoring insmartcomposites using free space facility. Such composites with magnetic microwire inclusions can present tunable magnetic permittivity. We report on in-situ the evolution of the transmission and reflection parameters of the polymer containing magnetic microwire inclusions during the polymerization process. A remarkable change of the reflection and transmission in the range of 4-7 GHz upon the matrix polymerization is observed. Observed dependencies are discussed in terms of the effect of the temperature and stresses variation on magnetic properties of glass-coated microwires during the thermoset matrix polymerization. Obtained results are considered as a base for novel sensing technique allowing non-destructive and non-contact monitoring of the composites utilizing ferromagnetic glass-coated microwire inclusions with magnetic properties sensitive to tensile stress and temperature.

Impact of stress and magnetic field in annealing process on GMI and GSI effect of CoFeSiB amorphous material

This study focuses on investigating the impact of various annealing methods on the giant magneto-impedance (GMI) and giant stress induced GMI (GSI) effects of Co68Fe4.5Si12.5B15 ribbons. The GMI and GSI effect of the ribbons were characterized by impedance ratio under different annealing methods. The results indicate that the ribbon annealed with appropriate current density and additive 100 MPa tensile stress in Joule annealing exhibits the significant GMI ratio enhancing by 19.43 %. The study also demonstrates the significant influence of magnetic field in annealing, with magnetic field annealing showing great potential to improve both the GMI and GSI effects, increasing them to 75.76 % and 25.8 %, respectively. These findings provide insights into the development of materials with high sensitivity and thermal stability for modern sophisticated sensors.

Monitoring structural transformations in metamagnetic shape memory alloys by non-contact GMI technology

Different applications based on metamagnetic shape memory alloy (MSMA) require monitoring the evolution of the martensitic transformation (MT) to optimize the actuation mechanism. To avoid interaction with the active material, a non-contact technique would be ideal. Nevertheless, non-contact detection involves complex methods like diffraction, optical analysis, or electromagnetic technology. The present work demonstrates that the MT can be monitored without interaction with the active material using a low-cost technology based on the Giant Magnetoimpedance (GMI) effect. The GMI sensor is based on a (CoFe)SiB soft magnetic wire submitted to an alternating current and whose second harmonic voltage variation allows to detect changes in the strength of the stray magnetic fields linked to the metamagnetic phase transition. The sensor has been tested using the MT of a NiMnInCo MSMA. A specific application for environmental temperature control using the non-contact GMI sensor is proposed.

Optimization of Magnetoimpedance Effect and Magnetic Properties of Fe-Rich Glass-Coated Microwires by Annealing.

As-prepared Fe-rich microwires with perfectly rectangular hysteresis loops present magnetization reversal through fast domain wall propagation, while the giant magnetoimpedance (GMI) effect in Fe-rich microwires is rather low. However, the lower cost of Fe-rich microwires makes them attractive for magnetic sensors applications. We studied the effect of conventional (furnace) annealing and Joule heating on magnetic-propertied domain wall (DW) dynamics and the GMI effect in two Fe microwires with different geometries. We observed that magnetic softness, GMI effect and domain wall (DW) dynamics can be substantially improved by appropriate annealing. Observed experimental results are discussed considering the counterbalance between the internal stresses relaxation and induced magnetic anisotropy associated with the presence of an Oersted magnetic field during Joule heating.

Non-linear GMI decoding in 3D printed magnetic encoded systems

The nonlinear giant magnetoimpedance (GMI) effect was explored as a highly sensitive sensing technology in 3D-printed magnetic encoded systems. Magnetic nanoparticles with low (magnetite, Fe3O4) and high (Co ferrite, Co0.7Fe2.3O4) magnetic remanence were embedded (10 wt.%) in a polymeric matrix of Polylactic Acid (PLA) and Poly-ε-caprolactone (PCL) and extruded in magnetic filaments to be 3D printed by the Fused Deposition Modelling technique (FDM). Two different geometries were constructed namely, individual magnetic strips and fixed barcoded pieces. The stray magnetic fields generated by the magnetic nanoparticles were detected through the non-linear (second harmonic) GMI voltage using a soft magnetic CoFeSiB wire as the nucleus sensor. The decoding response was analyzed as a function of the magnetization remanence of the nanoparticles, the distance between the individual magnetic strips, and the position (height) of the GMI decoding sensor. It has been shown that modification of the net magnetization direction of each individual fixed strip within the barcode geometry is possible through the application of local external magnetic fields. This possibility improves the versatility of the 3D binary encoding system by adding an additional state (0 without nanoparticles, 1 or -1 depending on the relative orientation of the net magnetization along the strips) during the codifying procedure.

Tuning the giant magnetoimpedance response of a glass-coated microwire reinforced polymer by in-situ laser annealing

The ability to modify the giant magnetoimpedance (GMI) effect in amorphous glass-coated ferromagnetic Co-based microwire reinforced polymer via laser irradiation is presented. Through in-situ laser annealing of microwires embedded into a polymer matrix, a 25 % improvement in the GMI response is demonstrated after only 4.9 min of annealing. This improvement is compared to a conventional oven anneal technique, requiring an hour of oven annealing, subsequent sample cooling and polymer casting. This unique in-situ technique offers a novel and expedient path toward tailorable multi-functional composites in the areas of tunable electromagnetic shielding, structurally integrated antennas and magnetic sensors.

Optimization of temperature stability and sensitivity of the giant magnetoimpedance effect in meander shaped Co-based amorphous ribbon using DC-biased current for sensor application

The influence of DC-biased current (I DC) on the longitudinal giant magnetoimpedance (GMI) effect in Co-based amorphous ribbon with a meander structure, taken from room temperature to 120 °C, has been investigated. The results show that I DC increases the temperature stability of the impedance of amorphous ribbon at 20 MHz. By deriving the expression of the transverse permeability according to a magnetization rotation model, we attributed the improved temperature stability to the combined effect of temperature and bias field H DC generated by I DC on the transverse permeability. It is also shown that I DC not only effectively inhibits the weakening of the GMI ratio at high temperature, but also significantly improves the GMI sensitivity. This will help to achieve sensitive low magnetic field measurement under large temperature fluctuation.

Giant Magnetoimpedance Effect of Multilayered Thin Film Meanders Formed on Flexible Substrates.

The giant magnetoimpedance effect of multilayered thin films under stress has great application prospects in magnetic sensing, but related studies are rarely reported. Therefore, the giant magnetoimpedance effects in multilayered thin film meanders under different stresses were thoroughly investigated. Firstly, multilayered FeNi/Cu/FeNi thin film meanders with the same thickness were manufactured on polyimide (PI) and polyester (PET) substrates by DC magnetron sputtering and MEMS technology. The characterization of meanders was analyzed by SEM, AFM, XRD, and VSM. The results show that multilayered thin film meanders on flexible substrates also have the advantages of good density, high crystallinity, and excellent soft magnetic properties. Then, we observed the giant magnetoimpedance effect under tensile and compressive stresses. The results show that the application of longitudinal compressive stress increases the transverse anisotropy and enhances the GMI effect of multilayered thin film meanders, while the application of longitudinal tensile stress yields the opposite result. The results provide novel solutions for the fabrication of more stable and flexible giant magnetoimpedance sensors, as well as for the development of stress sensors.

Giant Magneto-Impedance Effect Microcurrent Sensor Based on MEMS Technology

The performances of common magnetic sensors in the field of microcurrent detection are presented. The giant magneto-impedance (GMI) effect is summarized, and the possibility of picoampere microcurrent measurement using the GMI effect sensor is proved. The classical design scheme of the GMI effect current sensor is improved, and a GMI sensor chip model that can realize picoampere microcurrent measurement is preliminarily established, which lays a theoretical foundation for further development of GMI microcurrent sensor with high performance, small volume, and low cost.

Giant magnetoimpedance effect and dipolar interactions of FINEMET/IGZO/CoFeSiB composite ribbons

ABSTRACT The dipolar interactions were investigated through the giant magnetoimpedance effect in FINEMET/IGZO/CoFeSiB composite ribbons. The interface between the CoFeSiB film and FINEMET ribbon was separated by IGZO layer in FINEMET/IGZO/CoFeSiB composite ribbons, which effectively induced dipolar interactions. The dipolar interactions were analyzed by the peak position field (H p ) of giant magnetoimpedance effect and magnetic properties. The results show that the H p decreased with the increase of the IGZO layer thickness. These results suggest that the GMI ratio (58%) and characteristic frequency (800 kHz) were optimized. The composite ribbons have high GMI ratio and low frequency, which can be applied in magnetic field sensors.

Off-Diagonal Magnetoimpedance in Annealed Amorphous Microwires with Positive Magnetostriction: Effect of External Stresses

It was observed recently that the giant magnetoimpedance (GMI) effect in Fe-rich glass-coated amorphous microwires with positive magnetostriction can be improved significantly by means of post-annealing. The increase in the GMI is attributed to the induced helical magnetic anisotropy in the surface layer of the microwire, which appears after the annealing. The application of external stresses to the microwire may result in changes in its magnetic structure and affect the GMI response. In this work, we study theoretically the influence of the tensile and torsional stresses on the off-diagonal magnetoimpedance in annealed amorphous microwires with positive magnetostriction. The static magnetization distribution is analyzed in terms of the core–shell magnetic structure. The surface impedance tensor is obtained taking into account the magnetoelastic anisotropy induced by the external stresses. It is shown that the off-diagonal magnetoimpedance response exhibits strong sensitivity to the magnitude of the applied stress. The obtained results may be useful for sensor applications of amorphous microwires.

Functional Properties of Cobalt-Based Amorphous Ribbons with Different Demagnetizing Factor

Co-based rapidly quenched amorphous ribbons are soft ferromagnets with well-adjustable functional properties. Their effective magnetic anisotropy and magnetization processes depend on the preparation conditions and geometrical parameters. It was found that giant magnetoimpedance effect (MI) for the FeCoCrSiB ribbons without heat treatments after relaxation annealing and after stress annealing at 350∘C shows critical dependence on the value of the demagnetizing factor. The range of FeCoCrSiB ribbons lengths with a significant change in properties is considered in a comparative analysis of the experimental results and model calculations. Quantitative analysis of the contribution of the demagnetizing fields and surface magnetic charges are discussed as the main mechanism for reducing the GMI properties of amorphous ribbons. These data are important for the development of the ribbon-based devices for practical applications of microelectronics.