Maximum Magnetoimpedance Ratio Research Articles

Magnetoimpedance effect in NiFeP thin films deposited on Cu microwire through electrodeposition

Thin coatings of the Nickel–Iron–Phosphorous (NiFeP) alloy is electrodeposited onto copper microwire while varying phosphorus ion concentration in the bath. With increasing phosphorus ion concentration in the deposition bath up to 1 mM, reduced surface roughness, crystallite size and coercivity is witnessed which reflects in enhanced magnetoimpedance (MI) ratio of the plated wires. Maximum MI ratio of 378% and sensitivity of 25 %/Oe is observed at 100 kHz driving frequency for film deposited using 1 mM of P ion in the electrodeposition bath. This enhancement is associated with the reduction of crystallite size and magnetocrystalline anisotropy due to leading formation of amorphous deposits with the optimized incorporation of P atoms coupled with reduction of surface roughness. Additionally, the experimental results of MI measurements are compared with a analytical model and the model parameters related to the circumferential permeability of the NiFeP magnetic film is extracted from it. These parameters are further used to calculate the circumferential permeability of the samples, which is then mapped to a color-coded visualization of current density variation across the wire cross-section, providing a detailed insight into the impedance change.

MI-Sensor Element Features and Estimation of Penetration Depth and Magnetic Permeability by Magnetoresistance and Magnetoreactance of CoFeSiB Amorphous Wires

The magnetoimpedance (MI) of amorphous soft magnetic Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">68.15</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4.35</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12.5</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sub> wires produced by the in-rotating water quenching technique was systematically studied. The behavior of the MI-element designed for magnetic sensors was examined in an external longitudinal dc magnetic field in the low-frequency range (f ≤ 1 MHz) and at the beginning of the intermediate frequency range (2 MHz ≤ f ≤ 5 MHz). A critical frequency of about 5 kHz - 7 kHz was observed with an initial increase in the MI effect. A maximum MI ratio of 334% was recorded at 0.95 MHz in a magnetically saturated MI-element. The intermediate frequency range is explored using the magnetoresistive - MR and magnetoreactive - MX components of magnetoimpedance Z. The MI anisotropy field profile occurs in the MHz operating frequency range with values increasing up to 25 A/m, exhibiting frequency dependence. The magnetic penetration depth was calculated using experimental magnetoresistance data, and the values obtained were about 3 μm - 4 μm for 5 MHz, showing a saturation trend. The magnetic permeability is analyzed in the framework of the electromagnetic classical high-limit model of a cylinder, which includes penetration depth and magnetoreactance. In our experiments and calculations, the classical high limit is satisfied in the operating frequency range of a few MHz. The magnetic permeability peak value is about 35% lower than the comparable data of amorphous CoFeNiMoSiB glass-coated microwires.

Response of the magneto-impedance to the martensitic transformation of the Ni46Mn22Ga24Co4Cu4 shape memory microwire

Based on the frequency dependence and the sensitivity of magneto-impedance to anisotropy, temperature, frequency, and magnetic field were able to co-regulated the impedance signals. In this paper, we used the magneto-impedance technique to characterize the martensitic transformation of Ni46Mn22Ga24Co4Cu4 shape memory microwire. The phase transformation from martensite to austenite at 345–368 K was accompanied by the magnetic transition. There was a significant difference in the magneto-impedance between the two phases that was strongly dependent on the range of the excitation current frequency. Higher magneto-impedance was acquired in martensite with high anisotropy indicating its higher sensitivity to the magnetic field. Additionally, the structure of the martensite variants caused hysteresis in the magneto-impedance and the maximum magneto-impedance ratio of the two phases was obtained at a high frequency (50 MHz). The results of this indicate the potential applicability of magneto-impedance measurement in analyzing phase transformations.

Meander Thin-Film Biosensor Fabrication to Investigate the Influence of Structural Parameters on the Magneto-Impedance Effect

Thin-film magneto-impedance (MI) biosensors have attracted significant attention due to their high sensitivity and easy miniaturization. However, further improvement is required to detect weak biomagnetic signals. Here, we report a meander thin-film biosensor preparation to investigate the fabrication parameters influencing the MI effect. Specifically, we hypothesized that an optimal film thickness and sensing area size ratio could be achieved to obtain a maximum MI ratio. A meander multilayer MI biosensor based on a NiFe/Cu/NiFe thin-film was designed and fabricated into 3-, 6-, and 9-turn models with film thicknesses of 3 µm and 6 µm. The 9-turn biosensor resembled the largest sensing area, while the 3- and 6-turn biosensors were designed with identical sensing areas. The results indicated that the NiFe film thickness of 6 µm with a sensing area size of 14.4 mm2 resembling a 9-turn MI biosensor is the optimal ratio yielding the maximum MI ratio of 238%, which is 70% larger than the 3- and 6-turn structures. The 3- and 6-turn MI biosensors exhibited similar characteristics where the MI ratio peaked at a similar value. Our results suggest that the MI ratio can be increased by increasing the sensing area size and film thickness rather than the number of turns. We showed that an optimal film thickness to sensing area size ratio is required to obtain a high MI ratio. Our findings will be useful for designing highly sensitive MI biosensors capable of detecting low biomagnetic signals.

Protective effect of a diamond-like carbon film on cobalt-based magnetoimpedance sensors in the Presence of Moisturized air

High sensitivity of the magnetoimpedance (MI) sensors, and their dependence on the variation of the surface of the sensors, have limited their application in different environmental conditions, such as, moisturized air. Here, we studied the effect of moisture on a cobalt-based sensor in the MI ratio measurement. Scanning electron microscopy (SEM) images showed that the surface of the sensor after exposure to the moisture became rough. The effects of diamond-like carbon (DLC) film coated on a cobalt-based MI sensor were investigated with the aim of creating a stable MI sensor capable of working in various environmental conditions. No significant change was observed in the maximum MI ratio in different frequencies of the coated sensors after exposure to the moisture. SEM images showed that the surface of the DLC-coated cobalt-based ribbons (CBRs) remained almost unchanged after exposure to moisture. Measuring vibrating sample magnetometer showed that the variation in hysteresis loop in the coated sample after exposure to moisture is little. The appropriate stability of the DLC-coated CBRs in moisturized air can be useful for the development of amorphous ribbon-based MI sensors.

Magnetoimpedance study of nickel incorporated diamond like carbon thin films

The present work aims to investigate the magnetoimpedance (MI) behaviour of electrodeposited nickel incorporated carbon (Ni–C) composite thin films of varying nickel content. Ni–C thin films were synthesized by electrodeposition method at room temperature with low voltage. Low nickel content thin films exhibited diamond-like carbon (Ni–DLC) phase. Considering the variation of magnetoimpedance due to change in transverse magnetic permeability of Ni–C thin films, magnetoimpedance measurements were performed with frequency by applying dc magnetic field in the plane of the film in the range of −1000 Oe < H < 1000 Oe. MI measurements were carried out, by passing alternating current of 1 mA through the samples perpendicular to the magnetic field, at room temperature within a low excitation frequency (up to 100 kHz) range. Magnetoimpedance peaks were observed at 9 kHz in each thin film. Variations in the intensity of MI peaks with magnetic field were also observed. Maximum MI ratio achieved for our samples was 123%, while Ni–DLC thin film showed an MI of 110%. The values of maximum magnetoimpedance of the films were found to change with nickel content in the Ni–C thin films.

Magnetoimpedance Effect in the Ribbon-Based Patterned Soft Ferromagnetic Meander-Shaped Elements for Sensor Application.

Amorphous and nanocrystalline soft magnetic materials have attracted much attention in the area of sensor applications. In this work, the magnetoimpedance (MI) effect of patterned soft ferromagnetic meander-shaped sensor elements has been investigated. They were fabricated starting from the cobalt-based amorphous ribbon using the lithography technique and chemical etching. Three-turn (S1: spacing s = 50 μm, width w = 300 μm, length l = 5 mm; S2: spacing s = 50 μm, width w = 400 μm, length l = 5 mm) and six-turn (S3: s = 40 μm, w = 250 μm, length l = 5 mm; S4: s = 40 μm, w = 250 μm and l = 8 mm) meanders were designed. The ‘n’ shaped meander part was denominated as “one turn”. The S4 meander possesses a maximum MI ratio calculated for the total impedance ΔZ/Z ≈ 250% with a sensitivity of about 36%/Oe (for the frequency of about 45 MHz), and an MI ratio calculated for the real part of the total impedance ΔR/R ≈ 250% with the sensitivity of about 32%/Oe (for the frequency of 50 MHz). Chemical etching and the length of the samples had a strong impact on the surface magnetic properties and the magnetoimpedance. A comparative analysis of the surface magnetic properties obtained by the magneto-optical Kerr technique and MI data shows that the designed ferromagnetic meander-shaped sensor elements can be recommended for high frequency sensor applications focused on the large drop analysis. Here we understand a single large drop as the water-based sample to analyze, placed onto the surface of the MI sensor element either by microsyringe (volue range 0.5–500 μL) or automatic dispenser (volume range 0.1–50 mL).

Influence of current annealing on the magneto-impedance response of co-based ribbons arising from surface structural improvement

In this paper, influence of current annealing on the magneto-impedance (MI) response of the Co-based amorphous ribbons with chemical composition of Co68.15Fe4.35Si12.5B15 was investigated. In order to achieve a maximum MI ratio, ribbon samples were annealed under two different conditions: the atmospheric pressure and a vacuum pressure of 5 × 10−3 mbar. During the annealing process, the dc electric current passing through the ribbons improved the surface structure while also changing the magnetic properties, arising from heating of the samples under proper conditions. The annealing process not only induced transverse magnetic anisotropy in the ribbon but also decreased stresses generated during melt spinning processes, thus enhancing the corresponding MI response. Annealing at different times and currents were performed in order to achieve optimum conditions and reach the maximum MI. Our results showed that the MI ratio increased for the annealed samples at both vacuum and atmospheric pressures so that the maximum MI (288%) was obtained for current annealing (at 200 mA for 65 s) in the vacuum, being promising for sensor applications. On the other hand, AFM and XRD results confirmed that less surface roughness would provide a smaller stray field, which in turn would increase the MI ratio.

Parallel-line number dependence of magneto-impedance effect in multilayer permalloy [Ni80Fe20/Cu]N films

In this paper, we studied the magneto-impedance effect in multilayered [Ni80Fe20/Cu]N with variation in the number of parallel-line on Cu PCB substrate. The method used in this research is the electrodeposition at a room temperature with Pt as an electrode. The results show that the magneto-impedance ratio increases with the increase in the number of parallel-line on Cu PCB. The maximum magneto-impedance ratio obtained in Cu PCB substrate which four parallel lines were 4.5%. Likewise, frequency variation, the magneto-impedance ratio increases with increasing frequency.

Structural Characterization and Magnetoimpedance Effect of Current Annealed Co-Based Amorphous Ribbons at Different Ambient

The effect of current annealing in the air and vacuum on structure and magnetoimpedance (MI) response of Co68.15 Fe4.35 Si12.5 B15 amorphous ribbons was investigated. After 15 min of annealing, we found optimized currents where maximum MI ratio reached to 125 % and 160 % for annealing in the air and vacuum, respectively. Sample structures and their magnetic properties were investigated to explain the MI response after the annealing. Variation of MI responses can be correlated to the difference in the thermal conductivity of air and vacuum, field-induced anisotropy, and surface changes.

Synthesis and magnetic properties of amorphous Fe–Y–B thin films

Amorphous Fe–Y–B thin films have been successfully fabricated by direct-current magnetron sputtering, and the effects of annealing treatment on the microstructure and magnetic properties, especially coercivity and magneto-impedance ratio, were investigated systematically. After low-temperature heat treatments (below 673K), films still remain amorphous structure and their magnetic properties were largely enhanced due to stress release, e.g., the maximum magneto-impedance ratio increases from about 5.6–46.6% and the coercivity decreases from about 7.7–2.2Oe for as-deposited film and the film annealed at 573K for 1h, respectively. After high-temperature heat treatment at 673K, crystallization occurs, deteriorating magnetic properties (magnetic softness and magneto-impedance features) of the film. The Fe–Y–B thin film annealed at 573K for 1h, possessing good magneto-impedance effect and soft magnetic properties, might have potential application in micro-sized magnetic actuators.

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

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

Enhanced magneto-impedance in Fe73.5Cu1Nb3Si13.5B9 ribbons from laminating with magnetostrictive terfenol-D alloy plate

The authors report an amplified magneto-impedance (MI) in a laminated composite composed of a magnetostrictive terfenol-D plate and a Fe73.5Cu1Nb3Si13.5B9 ribbon that exhibits an intrinsic MI. When a dc magnetic field is applied to a laminated composite, the magnetostriction from the terfenol-D plate induces a giant stress that is simultaneously transferred to the ribbon, generating a stress-induced impedance (SI). Combining the terfenol-D magnetostriction and the SI of the ribbon produces an enhanced MI. The maximum MI ratio for the composite is ∼74%, which is ∼27 times higher than that for a single ribbon.

Tuning giant magnetoimpedance response of Fe75.5Si13.5B7Nb3Cu1 amorphous ribbon by laser ablation

An easy method of tuning the response of maximum magnetoimpedance (MI) ratio in Fe75.5Si13.5B7Nb3Cu1 amorphous ribbons was investigated by laser ablation. In order to obtain different GMI peak positions, the stripes were ablated by laser with different separations on the surface layer of the ribbon. When the stripes were parallel (or perpendicular) to the applied magnetic field, the peak location of maximum MI ratio would drift to larger (or smaller) external field. And the shift was correlated with the spaces between stripes. The applied fields corresponding to the minimum and maximum values of peak location are 13Oe and 49Oe at the frequency of 15MHz, respectively. The phenomenon can be explained by the anisotropy field induced by demagnetizing field after the laser ablation.

Giant magneto-impedance of iron whiskers

Magneto-impedance measurements on iron whiskers with 〈1 0 0〉 growth direction were performed at room temperature as a function of the applied longitudinal magnetic field and frequency of the applied current. A maximum magneto-impedance ratio of more than 60% was observed under the chosen experimental conditions. Calculations based on the standard skin effect formalism permit the determination of the complex values of the effective circumferential permeability and the skin depth. The observations on the particularly simple model system allow a very detailed analysis of the magneto-impedance contributions not having been possible for the much more complex systems studied.

High frequency magnetic behavior through the magnetoimpedance effect in CoFeB/(Ta, Ag, Cu) multilayered ferromagnetic thin films

We investigate the structural and magnetic properties and the magnetoimpedance effect of CoFeB/(Ta, Ag, Cu) multilayered thin films grown by magnetron sputtering. It is noticed that the peak of maximum magnetoimpedance ratio values for a given frequency, as well as its position in frequency, is varied according to the used non-magnetic metal. For the CoFeB/Ta and CoFeB/Ag multilayered films, peaks of 30% and 27%, respectively, are observed at localized frequency ranges. For the CoFeB/Cu multilayer, slightly smaller values are verified, but for a wide frequency range. The magnetoimpedance results are analyzed in terms of the mechanisms responsible for the impedance variations at different frequency ranges and the magnetic and structural properties of the multilayer.

Enhanced magnetoimpedance and field sensitivity in microstructure controlled FeSiCuNbB ribbons

Fe73.5Si13.5Cu1Nb3B9 and Fe77.2Si11.2Cu0.8Nb3.3B7.5 nanocomposite materials consisting of nanocrystalline phase in an amorphous matrix were obtained by heat-treatment of their precursor amorphous ribbons. The influence of structural modifications induced during the heat-treatment on soft magnetic properties and magnetoimpedance (MI) effect have been studied. The structural investigations on both these ribbons revealed the presence of two phases, fine grained Fe3Si phase and a residual amorphous phase on heat-treatment. The maximum MI ratio obtained in the present study is 95% at f = 4 MHz, for the optimized heat-treated Fe77.2Si11.2Cu0.8Nb3.3B7.5 ribbon. This is ascribed to the increase in magnetic permeability and decrease in coercive force and intrinsic resistivity. Moreover, a maximum magnetic field sensitivity (ξ) of 8.3%/Oe at f = 2.5 MHz is obtained, for the optimized nanocrystalline Fe73.5Si13.5Cu1Nb3B9 ribbon. This suggests that tailoring of the nanocrystalline microstructures induced by optimum heat-treatment conditions can result in obtaining excellent combinations of the magnetic permeability and resistivity. Our results indicate that these Fe-based nanocrystalline materials can be ideally used for low magnetic field and high frequency sensor applications.

Rotation-field annealing effect on magnetoimpedance of Co-based amorphous ribbons

A new annealing method, called the RFA method, is introduced to improve the magnetoimpedance (MI) effect in Co-based amorphous ribbons; e.g. VAC6025. This method includes applying a sufficiently large rotating field h R, with a frequency F from 1 to 100 Hz, when the ribbon sample has been at the annealing temperature T A (from 160 to 280 °C) for 1 h, and then is field-cooled to room temperature. The best achievements are that: [I] after the F = 1 or 50 Hz and T A = 200 °C RFA treatment, the maximum MI ratio (Δ Z/ Z) m = 72% and the maximum operating frequency f m = 0.6 MHz; [II] after the F = 50 Hz and T A = 160 °C RFA treatment, the maximum field sensitivity S m = 4.5%/Oe and the highest figure of merit FOM = 1.8% MHz/Oe; [III] since both of the optimal T As above are much lower than the crystallization temperature ( T X = 500 °C), the samples remain ductile after RFA. In conclusion, we believe that the RFA treatment can greatly improve the MI performance of the VAC6025 ribbons, since h R, operating at T A and/or below, can effectively randomize the magnetic anisotropy, and thereby reduce the effective (or average) anisotropy energy 〈 K〉. This is equivalent to stating that the RFA method is effective in enhancing the permeability or the Δ Z/ Z ratio of any amorphous ribbon sample, including VAC6025.

Magnetoimpedance effect of current-annealed CoNiFe/Cu microtubes

A cobalt/nickel/iron (CoNiFe) magnetic layer was electrodeposited on a 50-μm-diameter non-magnetic Cu wire in a sulphate bath using a constant voltage. Electrodeposited CoNiFe composite wires were submitted to current annealing at 540 mA. It was found that annealing time less than 1 min removes internal stresses produced during fabrication and that annealing times longer than 5 min induce circumferential anisotropy. Non-annealed sample showed a magnetoimpedance (MI) ratio of 412%. A maximum MI ratio of 583% was obtained after 1 min of current annealing.

Giant magneto-impedance in stress-annealed finemet/copper/finemet-based trilayer structures

The resistive and reactive components of magneto-impedance (MI) for finemet/copper/finemet sandwiched structures based on stress-annealed nanocrystalline Fe 75Si 15B 6Cu 1Nb 3 ribbons as functions of different fields (longitudinal and perpendicular) and frequencies have been measured and analyzed. Maximum changes of 700% and 450% in the resistive and inductive components of MI, respectively, have been obtained in 30–600 kHz frequency range. These large changes in MI are a direct consequence of the large effective relative permeability due to the closed magnetic flux path in the trilayer structure. The influence of perpendicular bias fields ( H per) in the longitudinal MI (LMI) configuration greatly improves the MI ratios and sensitivities. The maximum MI ratio for the resistive component increases to as large as 2500% for H per∼1 Oe. The sensitivity of the field dependence of resistive component of MI increases from 48%/Oe to 288%/Oe at 600 kHz frequency with the application of H per∼30 Oe. Such high increase in MI ratios and sensitivities with perpendicular bias fields are due to the formation the favorable (transverse) domain structures.