Magnetoimpedance Curves Research Articles

Electromagnetic modeling and analysis based on multilayer domain structure for GMI behavior in high frequency

Existing theoretical models on the frequency dependence of the magnetoimpedance (MI) in ferromagnetic microwires primarily describe the MI phenomenon at the limiting cases of lower MHz (<several hundred MHz) or higher GHz (>several GHz) ranges. However, in the intermediate region between these two ranges, known as the transition region, MI curves undergo complex transformations. These transformations have been documented in the literature, but their underlying causes remain poorly understood. Unambiguous knowledge of the domain structure and its correlation with MI properties is essential for elucidating this behavior. In this study, we have, for the first time, observed the inner core magnetic structure of Co-based microwires and revealed its relationship with the high-frequency MI effect. A distinct magnetic structure comprising longitudinal domains in the inner core (IC), circular domains in the outer shell (OS), and a transition region (TR) has been identified. This structure originates from compositional gradients and residual stresses during microwire fabrication. The IC/TR/OS structure manifests in the complex transformations of the MI behavior, exhibiting a turning point at GHz frequencies before the characteristic double MI peak. We developed a multilayer planar model that considers this more realistic magnetic structure, including the TR layer. This model successfully reproduces the key features of the MI curves and provides deeper insights into the high-frequency MI phenomenon. Our findings pave the way for optimizing the sensing capabilities of Co-based ferromagnetic microwires and demonstrate the potential of using high-frequency MI measurements to map their magnetic microstructures.

The study on the magnetic interaction between the duel magnetic layers and the FINEMET ribbon

Due to the sensitive magnetic field response of the GMI effect, the peak field in magneto impedance curves obtained from the composite magnetic ribbons shows great dependence on the magnetic interaction, which has gained intensive attention in the study of the diversity and the mechanism of magnetic interaction. In this work, FINEMET/Fe20Ni80/SiO2/Fe20Ni80 composite ribbons with a fixed thickness of outer Fe20Ni80 layer (200 nm) and variable thickness ratio of the inner Fe20Ni80 and SiO2 layers, ranging from the 1:4 to 4:1 were prepared. Then the GMI response was utilized to investigate the influence of the exchange couple and the dipole interaction to magnetic properties of the base ribbon. The experimental results indicated that additional SiO2 layer can successfully induce slight magnetic differences of the two Fe20Ni80 layers, which results in the emergence of four-peak GMI profiles. Besides, the frequency-dependent nature of the peaks was explored, revealing that both dipole interaction and exchange couple influence the magnetic properties, contributing to the occurrence of four-peak GMI curves. Thus, the insights presented in this work are thought to be valuable for understanding the mechanisms of multilayer composite ribbons in future sensing applications.

Asymmetric magnetoimpedance in exchange-biased systems

Magnetic systems with competing anisotropies generally exhibit asymmetry between the maximum amplitudes of the right and left maxima in a magnetoimpedance curve. Small errors in positioning the samples at the experimental setup may also produce such asymmetry. In this work, we present a study on the sources of the asymmetry between magnetoimpedance peaks in systems that present the exchange bias phenomenon, by comparing a phenomenological model to experimental data. A set of samples with different repetitions of the NiFe/FeMn exchange-biased bilayer was used in this study. From the frequency evolution of the asymmetry, together with magnetization curves, we were able to identify the sources for the observed magnetoimpedance asymmetry found on our experimental data.

Amorphous ribbons for GMI detection of stray fields FeOx magnetic filler of epoxicomposites

Magnetoimpedance (MI) effect in stress-annealed Co-based amorphous ribbon was studied in the states without and in presence of the magnetic epoxy composite of cylindrical shape. Iron oxide FeOx magnetic microparticles of different concentrations (0–70 wt.%) were used as a magnetic filler. The condition of stress annealing (350 °C, 1 h and 250 MPa specific load) were selected in order to insure the high MI sensitivity with respect to external magnetic field in the field of a few Oersted. The MI responses were modified in the presence of the magnetic epoxy composites due to the contribution of the stray fields of embedded microparticles. It was experimentally found that degree of the MI curves modification depended on the microparticles concentration. The MI characteristics were also dependent on the length-to-width ratio of the MI element. The most sensitive MI element under study showed a linear dependence with a 1 %/weightpercent microparticle concentration slope. Mathematical modeling using finite elements (FEM) protocol for the properties of short MI elements confirmed the results and highlighted the non-monotonic contribution of high-concentration composites to the MI responses.

Magnetic, magnetodielectric, and magnetoimpedance correlations in co-substituted (Co, Ho) KBiFe2O5 at room temperature

The exotic physical properties of unique brownmillerite KBiFe2O5 (HC0) are enhanced by co-substituting rare-earth Holmium (Ho) and transition metal Cobalt (Co), ion and establishing their interaction. Dielectric, structural, magnetic, magnetodielectric (MD), and magnetoimpedance (MI) properties of co-substituted KBi1−xHoxFe2(1−y)CoyO5 [x = y = 0, 0.05, 0.1, & 0.15] are investigated. The solid-state reaction method is used to synthesize, and the Rietveld refined powder X-ray diffraction patterns confirm the monoclinic structure with the P2/c space group. The Raman shift decreases, but the lattice strain increases with increased co-doping and correlates with MD data. The room temperature (RT) remnant (MR) and saturation (MS) magnetization increase by ∼ 20 and ∼ 2 times, respectively, with co-doping. The magnetic anomaly near dielectric transition (∼ 500 °C for KBi0.95Ho0.05Fe1.9Co0.05O5) suggests the signature of MD coupling for the co-doped samples. The MD and magneto-loss (ML) strength of HC0 increase with co-doping from 0.35 % to 0.65 % and 0.65 % to 1.25 %, respectively. In addition, the MD coupling coefficient increases from 4 % to 11 %, with the increase in co-doping. The RT MI curve of KBi0.85Ho0.15Fe1.75Co0.15O5 (HC15) shows an enhanced symmetric hysteresis loop (butterfly-like) with a maximum strength of ∼ 0.6 %. The frequency-dependent MD of HC0 shows that the maximum MD% at a high frequency (> 50 kHz) is enhanced with the increase in co-doping, and the corresponding MD and ML strength of HC15 are − 1.2 % and − 0.4 %, respectively. The dielectric relaxation time for HC15 shows maximum non-linear variation with the magnetic field, suggesting an intrinsic contribution to MD coupling. The observed dielectric transition (TC) around 510 °C of HC0 decreases to 480 °C (for HC15) with the increase in the co-doping. Thus, enhanced MD coupling and magnetic field-controlled dielectric relaxation for co-doped HC0 make this material suitable for next-generation spintronic and storage device applications.

Magnetic Critical Behavior, Hall and Magneto-Impedance Effects in Fe–Co-Based Metallic Glasses

A comparative study of the magnetic critical behavior, magnetic anisotropy, Hall and magneto-impedance effects, and magnetic interactions is presented for Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> and Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> metallic glasses. The critical behavior is studied by determining the critical exponents for zero-field magnetization (β), critical isotherm (δ), and critical temperature TC, from magnetization measurements using the method by Berger-Campillo et al. The corresponding (β, δ, and TC) values for Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> and Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> are (0.341 ± 0.008, 4.00 ± 0.27, and 644.5 ± 25.5 K) and (0.399 ± 0.014, 4.25 ± 0.44, and 460 ± 32 K), respectively. These β values indicate that the universality class of Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> is consistent with the 3-D XY model, whereas Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> seems to be more close to the 3-D Heisenberg model. These TC values indicate that the exchange interaction is weaker in Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> than in Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> . The Hall effect experiments reveal an ordinary and extraordinary contribution to the Hall effect and a positive Hall constant. Furthermore, the extraordinary Hall contribution and magnetic anisotropy decrease more rapidly in Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> than in Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> . The magneto-impedance curves exhibit the single-peak (SP) and two-peak (TP) behaviors. The possible magnetic interactions, including the spin-orbit interaction, the exchange interaction, and the magnetic dipolar interaction, might be active in these materials, and their possible effects on the β value are analyzed.

Influence of Multilayer Number to Magneto-Impedance Ratio in Electrodeposited [NiFe/Cu]&lt;sub&gt;N&lt;/sub&gt; Multilayer

Magneto-impedance ratio of the multilayer [NiFe/Cu)]N study by the number of multilayer. The both sample films of NiFe and Cu are fabricated by electrodeposition methods on a Cu-patterned substrate. The characteristic of magneto-impedance (MI) is performed at room temperature. Magneto-impedance are modified by varying N times (2, 4, 6 and 8) and the measurements frequency. The result show that the typical symetry of the magneto-impedance curve. Then the magneto-impedance (MI) ratio increases with the increase of frequency and N number layers. The increase of the magnetic permeability should address the increase of the MI ratio. Finally, the highest magneto-impedance ratio of 13.79 is obtained for [NiFe (200)/Cu (25)]8 at frequency 100 kHz.

Magneto-impedance in Multilayered [Ni80Fe20/Cu]4 with modification of the line-length pattern on Cu printed circuit board

Magneto-impedance of multilayer [Ni80Fe20/Cu]4 on Cu PCB substrate has successfully studied. To enhance the magneto-impedance we modify the geometry the Cu PCB substrate. The multilayer is made by electro-deposition with Pt (Platinum) as elctrodes. Electro-deposition is made at room temperature. Magneto-impedance total is evaluated under the external magnetic field. The results shows that magneto-impedance curve is symmetry. The difference of line-length result in the difference of the magneto-impedance. The samples is with the longest line-length has the largest magneto-impedance ratio. The homogeneity of the samples is on account estimated the increase magneto-impedance ratio.

Thin-Film Magnetoimpedance Structures Onto Flexible Substrates as Deformation Sensors

The magnetic and magnetoimpedance (MI) properties of a Permalloy-based thin-film structure, deposited onto a polymeric flexible substrate, are investigated as a function of the applied stress. The selected structure, a sandwich of NiFe/Ti multilayers with a central Cu layer, has been previously shown to produce extraordinary MI performance when deposited onto rigid substrates. Here, grown onto a cyclo olefin polymer substrate, it is evaluated as a deformation sensor and its properties analyzed in terms of the preparation conditions. A specially designed sample holder allows measuring simultaneously the hysteresis loop of the sample using magneto-optical Kerr effect and its MI using a network analyzer, while applying a controlled stress to the sample. The magnetoelastic anisotropy developed in the sample is longitudinal, revealing that the magnetostriction coefficient is positive, and competes with the transverse magnetic anisotropy induced during the sputtering deposition of the multilayer structure. The combined, effective anisotropy determines the shape of the hysteresis loop and the MI curves. We show how the evolution of the maxima of the MI curves with the applied stress allows a precise determination of the magnetostriction coefficient of the sample. The stress impedance is determined as the impedance change, measured at $H =0$ Oe, as function of the applied stress. It displays a linear behavior with a corresponding gauge factor of 60, thirty times larger than the one of conventional metallic strain gauges.

Magnetoimpedance and magnetic properties of Co72Fe5Ni10Cr5Si7B3 amorphous ribbons in different states

CoFeNiCrSiB amorphous ribbons have been prepared by rapid quenching and subjected to the post preparation heat treatments in air. Structure, magnetic properties and giant magnetoimpedance (MI) characteristics were investigated. Short annealing of the sample at 380°С for 4min leads to a useful structural relaxation and the highest MI ratio ΔZ/Z =350% for the total impedance. In as prepared state “two-peak” MI field dependences were well correlating with effective magnetic anisotropy features. Post preparation treatment resulted in clear transformation into “one-peak” shaped MI curve typical for the ribbons with longitudinal effective anisotropy. Corresponding decrease of the field sensitivity by the order of magnitude as a result of short heat treatments in air shows their importance.

Invariance of the magnetic behavior and AMI in ferromagnetic biphase films with distinct non-magnetic metallic spacers

We investigate the quasi-static magnetic, magnetotransport, and dynamic magnetic properties in ferromagnetic biphase films with distinct non-magnetic metallic spacer layers. We observe that the nature of the non-magnetic metallic spacer material does not have significant influence on the overall biphase magnetic behavior, and, consequently, on the magnetotransport and dynamic magnetic responses. We focus on the magnetoimpedance effect and verify that the films present asymmetric magnetoimpedance effect. Moreover, we explore the possibility of tuning the linear region of the magnetoimpedance curves around zero magnetic field by varying the probe current frequency in order to achieve higher sensitivity values. The invariance of the magnetic behavior and the asymmetric magnetoimpedance effect in ferromagnetic biphase films with distinct non-magnetic metallic spacers place them as promising candidates for probe element and open possibilities to the development of lower-cost high sensitivity linear magnetic field sensor devices.

Temperature dependence of the off‐diagonal magnetoimpedance in sensor configuration utilizing Co‐rich amorphous wires

For sensor operation, the temperature stability is of primary importance. In this work, we have investigated the temperature dependence of the magnetoimpedance (MI) in glass‐coated Co‐based amorphous wires which are widely used as MI sensing elements. The magnetic alloy has high Curie and crystallization temperatures, yet, the MI change at moderate temperatures of 20–90 °C and low‐magnetic fields can be about 100%. This is explained by high‐temperature sensitivity of the residual stress due to fast solidification and the difference in thermal expansion coefficients of glass and metal. To reduce the temperature effect, annealing treatment was proposed and applied to the whole sensing element in off‐diagonal configuration comprising the MI wire and detection coil. Annealing treatment at a temperature of 160 °C during 2–3 min makes it possible to significantly improve both the magnetic field sensitivity and temperature stability. After annealing, the output voltage sensitivity in the linear region ( increases more than 2.5 times and shows little variations with temperature up to 90 °C. For higher magnetic fields, the MI profile still shows noticeable change with temperature: the maximum of the output voltage decreases at a rate of about 0.15%/°C as the temperature is increased. After optimum annealing, the MI curves become almost symmetrical suggesting that a well‐defined circumferential anisotropy is established.

Role of the Co-based microwires/polymer matrix interface on giant magneto impedance response

The interface of Co-based microwires-epoxy composites was modified by applying silane treatment on the surface of the wires and their magneto impedance (MI) response was evaluated. The aim of the surface treatment was to modify the residual stresses that coexist at the microwires/polymer matrix interface and hence the magnetic anisotropy. X-ray Photoelectron Spectroscopy confirmed the covalent attachment of silane molecule onto the wires surface by the presence of Si–O–Si and Fe–O–Si. The MI curve changed from single peak for untreated samples to double peak behavior for treated samples with a significant improvement of MI ratio. Additionally, the magnitude of the anisotropy field increased with the frequency, which may imply a strongly non-uniform stress distribution towards the surface. The MI variation was explained by the change of the surface magnetic anisotropy owing to the modification of the microwires/polymer matrix interface.

Magnetoimpedance hysteresis in amorphous microwires induced by core–shell interaction

We report on magneto-impedance (MI) hysteresis at MHz and GHz frequencies in amorphous microwires subject to a sufficiently high applied axial magnetic field HE. We show that this hysteresis originates from the magnetic hysteresis of the inner core which biases the outer shell causing a shift of the MI curve along the HE axis. Combined experiments (longitudinal and off-diagonal MI Z(HE), hysteresis loops M(HE) by vibrating sample magnetometer, and induction method) reveal the details of the magnetization reversal process in these microwires: Partial field dependencies Z(HE) and M(HE) are shown to be practically anhysteretic but shifted to the left or to the right about the origin by a residual magnetic field of the inner core HC. This shift can vary in the range from −35 to +35 A/m, depending on the magnetic history of the sample. We demonstrate that the hysteresis can be suppressed by application of a high enough axial magnetic field that saturates the magnetization of the inner core. A potential application of this hysteresis for memory devices is also proposed.

Tunable asymmetric magnetoimpedance effect in ferromagnetic NiFe/Cu/Co films

We investigate the magnetization dynamics through the magnetoimpedance effect in ferromagnetic NiFe/Cu/Co films. We observe that the magnetoimpedance response is dependent on the thickness of the non-magnetic Cu spacer material. We verify asymmetric magnetoimpedance in films with biphase magnetic behavior and explore the possibility of tuning the linear region of the magnetoimpedance curves around zero magnetic field by varying the thickness of the spacer and probe current frequency. We discuss the experimental results in terms of the different mechanisms governing the magnetization dynamics at distinct frequency ranges, quasi-static magnetic properties, thickness of the spacer, and the kind of the magnetic interaction between the ferromagnetic layers. The results place films with biphase magnetic behavior exhibiting asymmetric magnetoimpedance effect as very attractive candidates for application as probe element in the development of auto-biased linear magnetic field sensors.

Angular dependence of asymmetric magnetoimpedance in exchange biased NiFe/IrMn multilayers

We investigate the angular dependence of asymmetric magnetoimpedance of NiFe/IrMn multilayers and explore the possibility of tuning the linear region of the magnetoimpedance curves by modifying the angle between the applied external magnetic field and exchange bias field, and probe current frequency. We quantify the sensitivity by calculating the ratio |ΔZ|/|ΔH| at low magnetic fields as a function of the frequency for samples cut with different orientations and show that considerable values in the linear region around zero field can be reached. The results extend the possibilities for application of exchange biased magnetoimpedance multilayers as probe element for the development and improvement of auto-biased linear magnetic field sensors.

Enhanced giant magnetoimpedance effect in patterned FeNi/FeCo nanostructure

Enhanced giant magnetoimpedance effect has been observed in FeNi/FeCo nanostructure. 50 nm thick patterned FeCo micrometer pillar with in-plane uniaxial anisotropy was deposited on the surface of 100 nm isotropous FeNi magnetic film. The diameter of FeCo pillar is controllable. Before magnetoimpedance measurement, electrodes were fabricated by laser ablation. All samples show a typical giant magnetoimpedance curves at different frequencies. The optimized giant magnetoimpedance ratio is more than 80% at 30 MHz, when the FeCo micro-pillar's diameter is 50 μm. The phenomenon can be explained by the enhanced transverse permeability of FeNi film which was induced by anisotropy FeCo pillars due to exchange-coupling effect at the interface.

Magnetoimpedance Effects in Electrodeposited NiFe Nanowire Array

In this work, NiFe nanowires were grown in highly ordered porous anodic alumina oxide templates by dc electrodeposition at a pH value of 2.6. Scanning electron microscopy showed that wires have diameters of about 250 310 nm and length 25 30 μm. The energy dispersive X-ray analysis showed that the composition of the nanowires is Ni65Fe35. Electrical contacts were made on both sides of the nanowire array and their magnetoimpedance properties were investigated. All the magnetoimpedance curves showed single peak behavior due to the high shape anisotropy. The maximum magnetoimpedance change at the 79 MHz driving current frequency was ≈ 1.45%.

Expanding the longitudinal magnetoimpedance sensor range by direct bias current

We investigated the effects of induced helical anisotropy and application of dc bias current IB on longitudinal magnetoimpedance (MI) in amorphous microwires both separately and together. We demonstrated that when both parameters are present, i.e., a dc bias current IB is applied to the microwire with induced helical anisotropy, the longitudinal MI sensor range can be considerably extended up to the fields considerably higher than its anisotropy field as the slope of MI curve dZ/dHE remains rather high. A highly asymmetric longitudinal MI dependence with a rather high slope at the zero-field point was obtained. Reversing the bias current IB causes reversal of the bias field direction and results in a mirroring of the MI dependence. This gives a possibility to determine both the sign and the magnitude of the external magnetic field. The obtained results can be used in development of the longitudinal MI sensors with increased sensitivity and/or range.

Magnetoimpedance effects in a CoNiFe nanowire array

This report describes the growth of CoNiFe nanowires into highly ordered porous anodic alumina oxide (AAO) templates by DC electrodeposition at a pH value of 2.6. Scanning electron microscopy (SEM) observations revealed that the wires have diameters of approximately 270–290nm and a length of 25μm. The energy dispersive X-ray (EDX) analysis indicated that the composition of the nanowires is Co12Ni64Fe24. Electrical contacts were created on both sides of the nanowire array, and their magnetoimpedance (MI) properties were investigated. The impedance value was initially 1.2ohm at low frequency and increased to approximately 1000ohm for a 33-MHz driving current frequency under no applied magnetic field. All the MI curves exhibited single peak behaviour due to the high shape anisotropy. The maximum MI change at the 33-MHz driving current frequency was 2.72%. The maximum resistance change was 5.4% at 33MHz.