Circumferential Permeability 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.

Magnetoimpedance effect in electrodeposited NiFe/Cu wire using trisodium citrate additive in plating bath

Magnetoimpedance (MI) and magnetic properties of the electroplated NiFe/Cu thin films with a steadily rising concentration of trisodium citrate (TSC) additive in the plating bath is systematically examined in a wide frequency range of 10 kHz–8 MHz. The addition of TSC to the plating bath reduces the crystalline size and coercivity of the NiFe film, resulting in increased magnetic softness and MI ratio. The grain refining action of TSC additive is responsible for the random distribution of magnetic anisotropy axis in individual tiny crystallite which enhance circumferential permeability of deposited film and its MI ratio. The optimum concentration of TSC additive is found to be 40 g/l and sample electrodeposited at that TSC concentration boosts the MI ratio to 113% as compared to 28% when no TSC is used. When the film is deposited without any additive, a typical double peak behavior of the MI response curve is exhibited at higher frequency. This feature is eradicated with slightest inclusion of TSC additive in the electrodeposition bath which is an indication that inclusion of trisodium citrate weakens the circumferential anisotropy in plated film. Based on the analytical formulation of circumferential permeability the results of MI measurements are mapped with the theoretical framework, and the circumferential permeability of the NiFe magnetic film is reconstructed by curve fitting. Through the investigation of the fitting parameters, it is found that the addition of TSC to the bath completely annihilates the circumferential anisotropy found in as deposited permalloy film which is responsible for the transition from double to single peak behavior of MI response at higher frequencies.

Influence of chromium doping on the magnetoimpedance of electrodeposited NiFeCr/Cu thin films for sensor applications

Magnetoimpedance (MI) effect in electrodeposited NiFeCr thin films on the Cu wire is studied for various doping concentrations of chromium (Cr) ion in the NiFe plating bath. The incorporation of Cr ion results in continuous reduction of crystallite size and surface roughness of the film deposited. The rms surface roughness and crystallite size of the film reduce from 33nm to 25nm and 9.1nm to 6.1nm respectively when the Cr ion concentration in plating bath is increased from zero to an optimal value of 0.06 mM. As a result, the coercivity of the film is reduced from 0.11 kA/m to 0.02 kA/m, resulting in increased magnetic softness as explained by random anisotropy model. The enhanced soft magnetic property reflects in MI ratio improved up to 313% with field sensitivity of 232%/(kA/m) as compared to MI ratio 168% and sensitivity 104%/(kA/m) when no Cr ion is introduced. Furthermore, an analytical model of circumferential permeability is used which considers distribution of relaxation time corresponding to domain wall motion and dispersion in circumferential magnetic anisotropy in spin rotation. Fit of the experimental data of impedance with theoretical equation of impedance in conjunction with this analytical model of circumferential permeability yields the material parameters related to circumferential permeability of NiFeCr films. These fitting parameters reveals that inclusion of Cr in permalloy film enhances its maximum value of circumferential permeability about 54% by increasing the contribution of domain wall motion and reducing the dispersion of circumferential anisotropy field.

Effects of Joule annealing on the magnetoimpedance characteristics of Nb-doped Co-based metallic microfibers

The microstructure and magnetic properties of Co-based metallic microfibers before and after Joule annealing were comprehensively investigated to enhance the magnetoimpedance (MI) effect of metallic microfibers and facilitate the development of magnetic sensor applications. In particular, high-resolution transmission electron microscopy was used to investigate the microstructural changes induced by Joule annealing and to, further elucidate the associated mechanism. The experimental results show that the microfibers have a smooth and homogeneous surface, with no apparent macro/micro defects, as well as high glass-forming ability and thermal stability. Additionally, the 90 mA-annealed microfibers exhibit good magnetic properties, and their M s , M r , H c , and μ m are 81.40 emu/g, 15.01 emu/g, 33.63 Oe, and 0.1471 nm, respectively. The 90 mA-annealed microfibers also exhibit excellent MI performance. Accordingly, the [Δ Z/Z max ] max and ξ max are 213.08% and 41.76%/Oe as f = 1 MHz, respectively. Therefore, the Joule annealing treatment can significantly improve the MI properties of Co-based metallic microfibers, providing technical support for the development of sensitive materials for high-performance MI sensors. The transient temperature rising characteristic of Nb-doped Co-based metallic microfibers during Joule annealing can be numerically calculated based on a non-stationary heat conduction model, further to obtain the optimum parameters of practical annealing process. Accordingly, the MI properties of metallic microfibers were enhanced especially at the current intensity of 90 mA. Furthermore, Joule annealing could effectively eliminate the residual inner stress and improve the atomic short-range ordering arrangement, and the current could generate a stably toroidal magnetic field, which further regulates the toroidal distribution of magnetic domain structure, thereby improves the circumferential permeability, magnetic anisotropy field and MI properties.

Giant magnetoimpedance effect in electrodeposited CoNiFe/Cu composite wire: Experimental study and analytical modelling

Study of giant magnetoimpedance effect (GMI) in electrodeposited CoNiFe/Cu composite wire is reported in the intermediate frequency region (10 kHz–10 MHz). The room temperature M–H curve of the sample reveals that the magnetic softness is independent of the film thickness(t). The changes in GMI value is attributed to the geometric effect caused by change of film thickness. To justify this claim, a hybrid model for circumferential permeability is proposed by combining the effect of domain wall motion(μdw), spin rotation (μrot) and local dispersion of anisotropy. The spectra of circumferential permeability is modelled with domain wall relaxation with continuous distribution of relaxation times. The spin rotation part of circumferential permeability is formulated using linearized Landau–Lifshitz–Gilbert (LLG) equation with Bloch–Bloembergen damping term and dispersion of anisotropy field. The proposed model is able to reproduce all the experimental results using single set of material parameters.

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

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

Engineering of Magnetic Softness and Domain Wall Dynamics of Fe-rich Amorphous Microwires by Stress- induced Magnetic Anisotropy

We observed a remarkable improvement of domain wall (DW) mobility, DW velocity, giant magnetoimpedance (GMI) effect and magnetic softening at appropriate stress-annealing conditions. Beneficial effect of stress-annealing on GMI effect and DW dynamics is associated with the induced transverse magnetic anisotropy. An improvement of the circumferential permeability in the nearly surface area of metallic nucleus is evidenced from observed magnetic softening and remarkable GMI effect rising. We assumed that the outer domain shell with transverse magnetic anisotropy associated to stress-annealing induced transverse magnetic anisotropy affects the travelling DW in a similar way as application of transversal bias magnetic field allowing enhancement the DW velocity. Observed decreasing of the half-width of the EMF peak in stress-annealed microwires can be associated to the decreasing of the characteristic DW width. Consequently, stress annealing enabled us to design the magnetic anisotropy distribution beneficial for optimization of either GMI effect or DW dynamics.

Mechanism of Permeability Evolution for Reservoir Sandstone with Different Physical Properties

Permeability of sandstones with different properties taken from Chongqing reservoirs has been measured and deeply discussed under increasing deviatoric stress. Corresponding to the distinct features in the stress-strain behaviors, the permeability of sandstones is found to evolve with a clear permeability decrease in the initial closure region, a constant permeability value in the elastic region, a permeability increase in the crack initiation and propagation region, a sharp permeability increase in the crack growth region, and a decrease permeability in the residual stage. The results also show that the variation patterns of permeability are similar for two reservoir sandstones under combination of confining pressure and water pressure; however, the strength and permeability are smaller for the sandstone with mud than that without mud, deeply indicating that mud-like materials have a relatively great impact on the mechanical properties and permeability, so mud components cannot be ignored for prediction of reservoir permeability. Furthermore, a statistical damage constitutive model considering hydraulic-mechanical coupling process is presented to calculate the damage variable D, illustrating that larger water pressure will result in a relatively smaller damage variables D and corresponding maximum, which explains that the permeability increases more rapidly and is larger for the sandstone without mud than that with mud, and sandstone damage related to corresponding circumferential crack strain and permeability has been investigated, also implying the evolution mechanism of permeability for two sandstones with different physical properties. Therefore, it is worth pointing out that rock physical properties have a great influence on the reservoir permeability under complex extraction conditions and cannot be ignored, which is necessary to improve the recovery ratio and productivity.

Electrical impedance measurements in reentrant Au-Fe alloys

We report on impedance experiments carried out in the reentrant alloys Au-Fe 18at.% and Au-Fe 21at.%. A spin-glass system Au-Fe 13.5at.% was also studied for comparison. Measurements cover an extended temperature interval including the paramagnetic state, the intermediate ferromagnetic-like phase and the low temperature reentrant regime. Several frequencies in the range 0.1–1.8MHz were applied. Magneto-impedance measurements were also performed in low magnetic fields applied parallel to the current orientation. From the impedance versus temperature data, the real and imaginary components of the circumferential permeability were extracted. A Hopkinson maximum is observed in both permeability components of the reentrant magnets. Also observed in these systems is a downwards inflexion in the permeability versus temperature curves at the canting temperature TK where the reentrant regime sets in. The anisotropy field HK was obtained from the magneto-impedance measurements in several temperatures spanning the ferromagnetic and reentrant states. A marked increase of the HK magnitude occurs in temperatures below TK, indicating the stabilization of the reentrant phase by the anisotropic Dzyaloshisnskii–Moriya coupling. These results are in agreement with predictions of the mean-field theory that explains canting and the reentrant state with basis on the freezing of the spin components which are transverse to the field orientation.

Tailoring giant magnetoimpedance effect of Co-based microwires for optimum efficiency by self-designed square-wave pulse current annealing

Herein, we systematically studied the effect of a novel square-wave pulse current annealing (SPCA) on the magnetic properties and microstructure of Co-based melt-extracted amorphous wires, and efficiently tailored the related experimental parameters by using numerical calculation of transient temperature rise during SPCA process. We obtained the optimal SPCA treatment (at 50Hz, with amplitude of 90mA for 480s) can remarkably enhance the GMI property of as-prepared wires. At 10MHz, the maximum GMI ratio [ΔZ/Z0]max and maxima response sensitivity ξmax of SPCA-treated wire increases to 202.60% and 305.74%/Oe, which is nearly two times and 1.5 times of 104.80% and 208.14%/Oe for as-cast wire, respectively. Especially, at 5MHz, [ΔZ/Z0]max of SPCA-treated wire increases to 185.81%, which is 2.5 times of 73.69% for as-cast wire, and ξmax of SPCA-treated wire increases to 346.65%/Oe by less than two times of 190.16%/Oe for as-cast wire. From mictrostructural perspective, the notably observed role of atomic order orientation regimes and circular magnetic domain during stress releasing or structural relaxation by the co-action of high-density pulse magnetic field energy and thermal activation energy determines the optimum efficiency of SPCA, further to enhance circumferential permeability. In conclusion, SPCA treatment is expected to effectively improve GMI property of microwires, which can be used as sensitive materials for potential sensor application in detecting weak magnetic field.

Magnetoimpedance and Field Sensitivity of CoFeSiB Amorphous Ribbons under Applied Tensile Stress

Magnetoimpedance (MI) and field sensitivity of CoFeSiB amorphous ribbons were investigated at frequencies ranging from 0.2 to 12 MHz after tensile stress applied. Experimental results indicate that the MI of amorphous ribbons can be significantly improved by applying a suitable longitudinal tensile stress. Applying tensile stress induces a rearrangement of domain walls which influences the circumferential anisotropy and magnetic permeability result in improving the MI response. The maximum MI response of 145 % and maximum field sensitivity of 6.32 %/Oe at frequency of 4 MHz were obtained, when tension was equivalent to 120 MPa. So the tensile stress as new method can be effective, cheap, and fast in sensor applications, and result of this investigation can be applied for the design of the stress sensors based on the giant magnetoimpedance effect.

Current-controlled giant magnetoimpedance of iron single crystals

Abstract Extended magnetoimpedance measurements on iron single crystals(whiskers) with 〈 100 〉 growth direction were performed at room temperature as a function of the applied longitudinal magnetic field and of the magnitude of the applied current in the low frequency regime. It is observed that there is a current threshold for inducing a giant magnetoimpedance effect. Calculations based on the standard skin effect formalism permit the determination of the effective circumferential permeability of the whiskers. It is found that the effect has its origin in the circumferential magnetic domain structure of the specimen. For comparison, impedance measurements on an iron wire were performed where no current threshold and continuous increase of the effective circumferential permeability is observed.

Tailoring of magnetic properties and GMI effect of Co-rich amorphous microwires by heat treatment

We studied effect of annealing on Giant magnetoimpedance (GMI) effect and magnetic properties of amorphous Fe and Co-rich microwires. High GMI effect has been observed in as-prepared Co-rich microwires. We observed that changing the annealing conditions we can obtain a great variety of properties in Co-rich microwire. High domain wall (DW) velocity and rectangular hysteresis loops we observed in heat treated Co-rich microwires. We observed increasing of the DW velocity under stress and coexistence of the GMI effect and fast DW propagation in the Co-rich microwires annealed at certain conditions. Fe-rich microwires with similar bulk hysteresis loop do not present considerable GMI effect. We assume that the outer domain shall of the annealed Co-rich microwire exhibiting both fast DW propagation and GMI effect has high circumferential magnetic permeability. Observed fast DW propagation in both kind of microwires is related to the fast magnetization switching within the single domain axially magnetized inner core, i.e. related to the remagnetization process of the inner part of the microwire.

Optimization of GMI properties by AC Joule annealing in melt‐extracted Co‐rich amorphous wires for sensor applications

We report here on a comprehensive study of an alternating‐current Joule annealing (ACJA) method for optimizing the giant magnetoimpedance (GMI) effect of Co‐rich amorphous wires for sensor applications. Experimental results indicated that the proper ACJA treatment can drastically improve the GMI property of as‐cast wire. At 10 MHz, the maximum GMI ratio [ΔZ/Z0]max of ACJA‐ed wire increase to 205.38%, which is nearly 3.3 times that of 62.84% for as‐cast wire, and the maxima field response sensitivity ξmax of ACJA‐ed wire increases to 345.90%/Oe by more than twice that of 170.92%/Oe for as‐cast wire. With an increase of AC amplitude, a remarkable dependence of GMI performance appears on the microstructural evolution such as the structural relaxation, the degree of local order, as well as circular magnetic domains. Importantly, the atomic order orientation incorporating HRTEM observation and circumferential permeability were effectively increased by the co‐action of thermal activation energy and magnetic field energy during ACJA, further to enhance the magnetic properties to some extent. Based on both the numerical calculation of transient temperature rise and GMI behavior, we propose ACJA as an efficient annealing technique to achieve simultaneous best performance of [ΔZ/Z0]max and ξmax for potentially magnetic sensor applications in detecting weak magnetic fields.

Combined current-modulation annealing induced enhancement of giant magnetoimpedance effect of Co-rich amorphous microwires

We report on a combined current-modulation annealing (CCMA) method, which integrates the optimized pulsed current (PC) and DC annealing techniques, for improving the giant magnetoimpedance (GMI) effect and its field sensitivity of Co-rich amorphous microwires. Relative to an as-prepared Co68.2Fe4.3B15Si12.5 wire, CCMA is shown to remarkably improve the GMI response of the wire. At 10 MHz, the maximum GMI ratio and its field sensitivity of the as-prepared wire were, respectively, increased by 3.5 and 2.28 times when subjected to CCMA. CCMA increased atomic order orientation and circumferential permeability of the wire by the co-action of high-density pulsed magnetic field energy and thermal activation energy at a PC annealing stage, as well as the formation of uniform circular magnetic domains by a stable DC magnetic field at a DC annealing stage. The magnetic moment can overcome eddy-current damping or nail-sticked action in rotational magnetization, giving rise to a double-peak feature and wider working field range (up to ±2 Oe) at relatively higher frequency (f ≥ 1 MHz).

Stress effects on complex permeability spectra of Mn-substituted cobalt ferrite

The effects of axial applied stresses on the magnetization processes in Mn-substituted cobalt ferrite (CoMnxFe2-xO4 with x = 0 to 0.4) toroids have been studied by measuring the circumferential complex permeability spectra μ* = μ′ − iμ″ from 1 kHz to 15 MHz. The μ* spectra were described using a dispersion equation to determine the relative susceptibilities due to domain wall motion (χD0) and magnetization rotation (χS0). Mn-substitution into cobalt ferrite was found to reduce the magnetocrystalline anisotropy and hence the susceptibility is increased. Under axial compressive stresses, χD0 and χS0 of all samples decrease. The Mn-substituted samples with x = 0.2 and 0.3 show larger reductions in χD0 and χS0 than the pure cobalt ferrite. The stress effects on χS0 and the dependence of the magnetomechanical effect on Mn content were reproduced in model calculations by taking into account the combined effects of stress-induced and magnetocrystalline anisotropies on magnetization rotation.

Enhancing GMI properties of melt-extracted Co-based amorphous wires by twin-zone Joule annealing

The influence of twin-zone Joule annealing (TJA) on the microstructure and magnetic properties of melt-extracted Co68.2Fe4.3B15Si12.5 amorphous microwires has been investigated. Experimental results indicated that twin-zone Joule annealing treatment improved the GMI property of as-cast wires to a greater extent comparing with Joule annealing (JA) and conventional vacuum annealing (CVA) techniques. At 15MHz, e.g., the maximum GMI ratio [ΔZ/Z0]max of a TJA wire increases to 104.29%, which is more than 5 times of 20.49% for the as-cast wire, nearly two times of 56.47% for the JA wire, while the CVA wire has a decreased GMI ratio; the field response sensitivity of the TJA wire increased to 171.62%/Oe from 80.32%/Oe for the as-cast wire, exceeding the values of 140.76%/Oe for the JA wire and of 39.17%/Oe for the CVA wire. The stress or structural relaxation in TJA wire increases circumferential permeability, and magnetic moment achieves a critical state of excitation for overcoming eddy-current damping or “nail-sticked” action in rotational magnetization process at relatively high frequency. From the microstructural point of view, the role of regularly arranged atomic micro-regions (RAAM) and of medium range order region (MROR) determines the efficiency of various annealing techniques. Conclusively, TJA is established as an efficient annealing technique to enhance the GMI effect of wires, which can subsequently be used for detecting weak magnetic field at relatively wider working range (±2.0Oe).

In situ microwave characterization of microwire composites with external magnetic field

Rubber composites containing Co68.15Fe4.35Si12.25B15.25 glass-covered amorphous microwires were fabricated. For samples containing 5 mm long wires and randomly dispersed in the polymer matrix, our results demonstrate that the current induces resonance of circumferential permeability (magnetoimpedance resonance) resulting in a significant change of the effective permittivity of the wire-filled composites with application of a high magnetic field. For samples containing longer wires (70 mm) periodically arranged in the polymer matrix, the permittivity spectrum shows two resonance peaks due to, respectively, dipole and magnetoimpedance resonance. The induced magnetoimpedance resonance has a narrower linewidth than the dipole one as magnetic field is increased.

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.

Impedance and Magnetic Permeability of Soft Ferromagnetic Metals

We report on impedance measurements in the Heusler compound Pd2MnSn, Gd metal and the re-entrant alloy Au0.82Fe0.18. Using a computational procedure, the real and imaginary components of the circumferential permeability could be determined from the complex impedance data. We show that the temperature dependence of the permeability is useful to study magnetic phase transitions, whereas valuable information on domain-wall motion and spin rotation processes may be obtained from appropriate analyses of the frequency and external magnetic field dependences of the complex permeability.