Giant Magnetoimpedance Response Research Articles

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.

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.

Low Frequency Giant Magneto-Impedance Effect of Co-Rich Ribbons Induced by Joule Annealing Treatment

The giant magneto-impedance (GMI) effect of Co83.2Fe5.2Si8.8B2.8 ribbons at frequencies of <1 MHz was analyzed. To improve the GMI response, a Joule annealing treatment was conducted with a direct current, and the domain structure of the ribbon surface was investigated via magneto-optical Kerr effect microscopy. The annealed ribbons show larger impedance changes under external magnetic fields, and higher field sensitivity is obtained by certain current annealing treatments. The field sensitivity of 418 and 782%/(kA/m) at 0.2 MHz and 0.8 MHz are achieved after annealing at 0.8 A for 20 min. The annealing treatment under direct electric current induces stress relaxation, and domain rearrangement, and the crystallization process gradually increases with the increasing current density, which gives rise to anisotropic reformation. The release of stresses due to Joule heating below the crystallization temperature causes the homogenous distribution of stress induced by rapid solidification and influences the elastic anisotropy, causing the domain structures to become much more regular. The crystallization, along with the precipitation of hard magnetic phases, increases the crystal anisotropy and induces the intense magnetic coupling action. Consequently, the magnetic domains in the annealed ribbons are rearranged with reformed anisotropy by Joule annealing heat and by the transverse magnetic field induced by the current. The irregular domains, with complex anisotropy in the as-cast ribbons corresponding to the weak GMI response, are transformed into regular and strip-like domains, with transverse easy magnetization after annealing at 0.4 A. After annealing at 0.8 A, the domains are further transformed into fine axial fingerprint-like domains, which are much more sensitive to the change in the axial external magnetic field, allowing for the best GMI response. These results indicate that the Joule annealing treatment is an optional method to optimize the soft magnetic properties and the GMI effect of these Co-rich ribbons at low frequencies.

Large Linear Giant Magneto-Impedance Response of Microwire Annealed under Liquid Medium for Potential Sensor Applications

Herein, we have presented the giant magneto-impedance (GMI) effect, microstructure and surface domain structure of the Co-Fe-based amorphous microwires after liquid medium—anhydrous ethanol Joule annealing (AJA). The AJA technique can effectively release the radial stress and induce large a circumferential magnetic field by changing the Joule heat transfer and the circumferential domain, to further tune the GMI performance of microwire. The linear response fields (0~3.5 Oe), the high sensitivity of 124.1%/Oe and the high GMI ratio make the microwire as promising materials for the miniaturized GMI sensors. The GMI ratios of [ΔZ/Z0]max(%) and [ΔZ/Zmax]max(%) increase the near-linearly to 201.9% and 200.5%, respectively, for the 250 mA anhydrous ethanol Joule annealed wires. Moreover, a linear response to Hex (ranging from 3.5 to 25 Oe, or more) is observed, which bears the potential in fabricating bi-sensors.

Improvement of high frequency giant magnetoimpedance effect in CoFeSiB amorphous ribbon with vanishing magnetostriction by electrodeposited Co coating surface layer

The influence of a ferromagnetic cover layer on giant magnetoimpedance (GMI) effect in nearly-zero magnetostrictive Co66.5Fe3.5Si12.0B18.0 amorphous ribbon after being surface coated by an electrodeposited Co layer of 10 μm in thickness, has been studied in the high frequency range between 10 MHz and 1.5 GHz. Longitudinal MOKE measurements performed on both kind of samples reveal the influence of exchange coupling interaction at the interface between the magnetic amorphous ribbon and electrodeposited Co coating layer, which is sensitive to the skin depth effect at high ac current frequency values. Comparison between GMI responses of the Co coated amorphous ribbon and the as-cast sample is provided. A more sharp and well defined double-peaks dependence of impedance on magnetic field, but with lower peaks intensity, is observed for the Co coated ribbon in the frequency range of 10–100 MHz, while the peaks intensity is higher than that observed in the as-cast ribbon at the high frequency value of 1 GHz due to the higher resistance of the Co electroplated layer than the core one. The influence of a dc bias drive current on the GMI response in both amorphous ribbons (as-cast and Co layered) is analyzed, which originates the removal of magnetic domain structure from both, the as-cast and Co-coated ribbons, giving rise more sensitive GMI effect. CoFeSiB amorphous ribbon with vanishing magnetostriction can achieve improved high frequency magnetic properties after being surface coated with electrodeposited ferromagnetic layers, as outstanding candidates for electromagnetic and magnetomechanical engineering applications.

Optimization of the high-frequency magnetoimpedance response in melt-extracted Co-rich microwires through novel multiple-step Joule heating

The optimization of the high frequency giant magnetoimpedance (GMI) effect and its magnetic field sensitivity in melt-extracted Co 69.25 Fe 4.25 Si 13 B 12.5 Nb 1 amorphous microwires was systematically studied through a multi-step Joule annealing (MSA) technique. The surface morphology, microstructure, surface magnetic property, and radio frequency GMI response of the Co-rich microwires were explored using techniques like microscopy, magneto-optical Kerr effect (MOKE) magnetometry, and the magnetic field dependence of the wire's radio frequency impedance (GMI). The multi-step Joule annealing protocol begins with an initial dc current amplitude ( i dc ) of 20 mA that was stepped up by 20 mA every 10 min to a maximum amplitude of 300 mA. Radio frequency GMI measurements at 20 MHz demonstrated a remarkable improvement of the GMI ratio and field sensitivity to 760% (1.75 times of that of the as-prepared wire) and 925%/Oe (more than 17.92 times of that of the as-prepared wire), respectively, after the MSA protocol with a maximum current amplitude of 100 mA. Microscopy and MOKE suggest that the MSA technique can enhance the microstructure and surface magnetic domain structure of the Co-rich magnetic microwire, which would give rise to an improved GMI ratio. The high GMI sensitivity at small magnetic fields renders these MSA-treated Co-rich microwires highly promising materials for biomedical devices that sense and monitor small, biological magnetic fields.

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.

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.

ZnO thin layer/Fe-based ribbon/ZnO thin layer sandwich structure: Introduction of a new GMI optimization method

Giant magneto-impedance (GMI) investigations comprising ZnO thin layers have received considerable attention for sensitive sensor applications. Herein, a ZnO thin layer with different thicknesses (92–503 nm) was deposited on surface of Fe-based amorphous ribbon (FeCoSiB) using RF magnetron sputtering. The GMI response and magnetic field sensitivity were investigated. While GMI% increased continuously up to the thickness of 223 nm, further increasing the ZnO thin layer thickness decreased GMI response. The GMI response and magnetic field sensitivity increased from 156% and 1.21%/Oe to 237% and 2.91%/Oe for bare Fe-based ribbon and ZnO thin layer/Fe-based ribbon/ZnO thin layer sandwich structure (223 nm in thickness), respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize ZnO-enhanced structural parameters. A vibrating sample magnetometer (VSM) was used to indicate the role of the ZnO thin layer in the GMI response. Similar increasing and decreasing trends of GMI% as a function of thickness were observed in transverse permeability of samples as determined by VSM. Our results provide a simple approach to achieve high GMI response and magnetic field sensitivity by using a dielectric sandwich structure.

Fabrication of FM/NM/FM Hetero-Structure Multilayers and Investigation on Structural and Magnetic Properties: Application in GMI Magnetic Sensors

Magnetic thin films of Fe/Cu/Fe and Fe/Cu/Ni multilayers on glass substrates were deposited by thermal evaporation route. The structure and morphology of multilayers were studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). Amorphous formation of the Fe and Ni in multilayer structures and the maximum surface roughness of about 6.11 nm for the Fe/Cu/Fe and 4.8 nm for the Fe/Cu/Ni thin films were observed. Also, magnetization behaviors in perpendicular and parallel fields to the surface were investigated. The behavior of the magnetization indicates a low 5-mT coercive field, the easy in-plane magnetization, and the formation of soft ferromagnetic structure. The giant magneto-impedance response (GMI) to the applied longitudinal magnetic field at 5-MHz frequency was obtained 70% for three-layer Fe/Cu/Fe. Also, the measurements for the Fe/Cu/Ni film show a peak in the external field of about Hext = 14 Oe and the GMI response of about 95% at 5-MHz frequency. This work provides a preliminary investigation into the high performance of multilayer-based GMI devices for sensor applications.

High frequency giant magnetoimpedance effect of a stress-annealed Fe-rich glass-coated microwire

Processing by stress-annealing (450 MPa, 300 °C, 1 h) the glass-coated microwire of Fe75B9Si12C4 composition a macroscopic magnetic anisotropy with a circular component is developed. This anisotropy very significantly improves the giant magnetoimpedance (GMI) effect with respect to the observed in the as-prepared microwire. The analysis of the GMI response as a function of the frequency (10–1000 MHz) opens new lights to understand the distribution of the magnetic anisotropy inside the glass-coated microwire.We have investigated the GMI response of the stress-annealed Fe75B9Si12C4 glass-coated microwire. From the frequency dependence of the GMI we have analyzed the distribution of the magnetic anisotropy inside the metallic nucleus obtaining good agreement with the average value of the anisotropy field deduced from the hysteresis loop of the bulk.From measured magnetic field dependences of GMI ratio we evaluated the frequency and magnetic field dependences of the penetration depth. We found that the minimum penetration depth of Fe75B9Si12C4 microwire decreases from about 1.5 μm down to 0.8 μm after stress annealing.Obtained dependences demonstrate that the minimum penetration depth value as well as the frequency and magnetic field dependences are considerably affected by the stress-annealing.

Dipolar interaction in multiple FINEMET ribbons

Abstract The dipolar interaction between FINEMET ribbons was investigated using giant magneto-impedance (GMI) measurement. It can be clearly revealed via the GMI response of a probe ribbon surrounding by nanocrystalline ribbons, which exhibited a plateau in the lower field region and double-peak in higher region. The plateau was gradually broadened with increasing the number of the surrounding ribbons or decreasing its length and the peak position shifted to higher field at the meantime. The frequency also affects the shift of the GMI peak field of the probe ribbon at high driving frequency, but has slight influence on the plateau in the measurement frequency range. Furthermore, the dipolar field between one surrounding ribbon and the probe ribbon and the geometric factor of ribbons are calculated using dipolar magnetization model to explicate the variation of dipolar interaction with number and length of ribbons. Thus, the GMI response of a probe ribbon can be employed as a novel tool to investigate the dipolar interaction in FINEMET ribbons.

Enhancement of Giant Magneto-Impedance in Series Co-Rich Microwires for Low-Field Sensing Applications

Two soft ferromagnetic Co68.25Fe4.25Si12.25B15.25 microwires with the same diameter of 50 ± 1 μm but different fabrication processes were placed in series and in parallel circuit configurations to investigate their giant magneto-impedance (GMI) responses in a frequency range of 1–100 MHz for low-field sensing applications. We show that, while the low-field GMI response is significantly reduced in the parallel configuration, it is greatly enhanced in the series connection. These results suggest that a highly sensitive GMI sensor can be designed by arranging multi-wires in a saw-shaped fashion to optimize the sensing area, and soldered together in series connection to maintain the excellent magnetic field sensitivity.

Magnetoimpedance effect in FINEMET/Ni80Fe20 composite ribbons

Giant magnetoimpedance (GMI) always attracts much attention owing to its importance in promising applications of industrial devices. Although GMI effect of ribbons have been studied for years, the composite ribbons coated with various films are still attractive due to its high sensitivity with respect to the applied magnetic field. Mostly, the magnetic properties were commonly inspected by hysteresis loops, which may not sensitive enough for Fe-based composite ribbons. Herein, by using both hysteresis loops and the GMI measurement, the magnetic properties of the FINEMT ribbons coated with different thickness of Ni80Fe20 film on free side, wheel side and twin sides have been thoroughly analyzed. It is revealed that the shift of anisotropy direction from preferable transverse to partially longitudinal as the film thickness increased, which affected the interaction between ribbon and Ni80Fe20 coating. Moreover, the asymmetric GMI response could be obtained on the ribbon coated with Ni80Fe20 film on single side, whereas the symmetric GMI response was observed for twin-side coating, which indicated the dipole interaction in the composite ribbons. We found that the ribbon with 260 nm Ni80Fe20 film showed the optimized transverse anisotropy, leading to the smallest Hc and the optimal soft magnetic properties. Hence, GMI measurement can be a sensitive alternative tool to investigate dipole interaction, which can be employed to manufacture novel linear GMI sensors and to properly regulate the operation field.

In-plane omnidirectional magnetic field sensor based on Giant Magneto Impedance (GMI)

In this work the design and characterization of an omnidirectional in-plane magnetic field sensor are presented. The sensor is based on the Giant Magneto Impedance (GMI) effect in glass-coated amorphous microwires of composition (Fe6Co94)72.5Si12.5B15. For the first time, a circular loop made with a microwire is used for giving omnidirectional response. In order to estimate the GMI response of the circular loop we have used a theoretical model of GMI, determining the GMI response as the sum of longitudinal sections with different angles of incidence. As a consequence of the circular loop, the GMI ratio of the sensor is reduced to 15% instead of 100% for the axial GMI response of a microwire. The sensor response has been experimentally verified and the GMI response of the circular loop has been studied as function of the magnetic field, driven current, and frequency. First, we have measured the GMI response of a longitudinal microwire for different angles of incidence, covering the full range between the tangential and perpendicular directions to the microwire axis. Then, using these results, we have experimentally verified the decomposition of a microwire with circular shape as longitudinal segments with different angles of incidence. Finally, we have designed a signal conditioning circuit for the omnidirectional magnetic field sensor. The response of the sensor has been studied as a function of the amplitude of the incident magnetic field.

Influence of Aspect Ratio on Giant Magnetoimpedance Effect for Fe67Co18Si11B4 Amorphous Ribbons

The effect of sample geometry aspect ratio (l/w) on the giant magnetoimpedance (GMI) in Fe67Co18Si11B4 amorphous ribbons was investigated systematically. The GMI profiles were measured as a function of the external magnetic field at different frequencies up to 110 MHz. The results show that there exists a critical aspect ratio ((l/w)0 = 5.4) below which the maximum GMI effect and sensitivity η decrease with decreasing l/w and above which the maximum GMI effect keeps almost constant and η decreases with increasing l/w. The observed dependence on aspect ratio as (l/w) < (l/w)0 is correlated with the magnetization process: Complex domain structures emerged near the ribbon ends to decrease the magnetostatic energy, modify the transverse permeability and consequently GMI response. Contributions from transverse permeability and resistance may dominantly determine the change of GMI effect as (l/w) > (l/w)0.

Nanostructured materials for magnetic biosensing.

Abstract Background Magnetic nanoparticles (MNPs) are at the leading edge of the field of biomedical applications and magnetic biosensing. Methods MNPs were fabricated by electrophysical methods of the laser target evaporation (LTE) and spark discharge with electrodynamic acceleration of plasma jumpers (SD). Synthesis of polyacrylamide hydrogel was done in the presence of Fe2O3 MNPs in different concentrations obtained by LTE. [FeNi/Ti]3/Cu/[Ti/FeNi]3/Ti multilayers for giant magnetoimpedance (GMI) based sensitive elements were prepared by rf-sputtering for testing a biosensor prototype. Results Iron oxide MNPs, ferrofluids, ferrofluids contacting with biological systems, synthetic ferrogels mimicking natural tissues – are the steps of the discussed in this work development of bionanomaterials. Thorough the structural and magnetic studies of a multilayered sensitive element, MNPs and ferrogels insure the complete characterization of biosensor prototype. The GMI responses were carefully evaluated in initial state and in the presence of ferrogel with known concentration of MNPs. SD MNPs had the smallest 5–8 nm size. This nanomaterial was characterized by large internal strains of the order of 25 × 10− 3, which can play an important role for the interaction with different biosystems. Conclusions Iron oxide MNPs were fabricated by LTE and SD methods. SD MNPs had the smallest 5–8 nm size and large internal strains of the order of 25 × 10− 3. Designed GMI biosensor prototype allowed precise evaluation of the stray field of the MNPs present in the ferrogel by evaluating the systematic changes of the GMI in a 20–400 MHz frequency range. General significance This work summarizes recent developments in the field of nanomaterials potentially applicable in magnetic biosensing.

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.

Magnetoimpedance effect of FINEMET ribbons coated with Fe20Ni80 permalloy film

To study the electromagnetic interaction mechanism between different soft magnetic materials, a series of specimen with different thickness Ni80Fe20 film were deposited onto nanocrystalline Fe73.5Cu1Nb3Si13.5B9 ribbons by magnetron sputtering. X-ray diffraction revealed a slightly structural variation of the ribbons as thickness of the Ni80Fe20 film ranging from 0 to 520 nm. The surface roughness of Ni80Fe20 layer was investigated by Atomic Force Microscopy, showing no significant variation with different thickness of Ni80Fe20 layer. The hysteresis loops and the coercivity value indicated the shift of anisotropy direction from parallel to normal to the surface as the Ni80Fe20 thickness increased, thus influencing the magnetic exchange interaction. Compared to the bare Fe73.5Cu1Nb3Si13.5B9 ribbons, coating of Ni80Fe20 films significantly enhanced the giant magnetoimpedance response of the ribbons. The 24% improved GMI ratio was achieved in the ribbon with 260 nm thick Ni80Fe20 film.

The Influence of Series and Parallel Current Flowing Through Two Paralleled Co-based Amorphous Wires on Giant Magneto Impedance Effect

Background: Giant Magneto Impedance (GMI) is effectively enhanced by the mutual magnetic interaction between two wires arranged in parallel setup. The direction of current flowing through two wires (series or parallel current mode) has a key role in this change. Methods: The aim of this research is to study the GMI properties of series and parallel current flowing through two amorphous Co-based wires in parallel setup and compare it to a single wire. Therefore, the wires with stoichiometric formula Co 68.15 Fe 4.35 Si 12.5 B 15 were prepared by in-rotating water spinning method with diameter about 125 μm. Findings: The best GMI response measured in series current mode and 8 mm distance between two wires. The GMI ratio increases from 300% of single wire to 480% of two wires in series current mode. However when the current flowing through two wires is in parallel mode, the GMI ratio decreases to 180% which is due to reduction of effective magnetic field. For two-wire system in series current mode, the magnetic interaction is stronger than parallel current configuration. Application: These results demonstrate that the GMI response could be effectively improved in two-wire series current system, which is useful for the application of low dimension and high sensitive GMI sensors.