Magnetic Impedance Research Articles

Construction of 2D/2D heterostructure with porous few layer g-C3N4 and NiCo2O4 nanosheets towards electromagnetic wave absorption

Developing high-performance materials with ultra-high reflection loss (RL ≤ -65 dB) for electromagnetic wave (EMW) absorption is pivotal to address electromagnetic pollution, but it is still challenging. Herein, a two-dimensional (2D)/2D PFL g-C3N4/NiCo2O4 heterostructure with porous few-layer g-C3N4 (PFL g-C3N4) and ultrathin NiCo2O4 nanosheets has been prepared by self-assembly, hydrothermal reaction, and calcination strategies. The 2D/2D heterostructure exhibits extraordinary EMW absorption property, achieving a reflection loss (RL) value of -68.59 dB and an effective absorption bandwidth (EAB) of 1.92 GHz at a matching thickness of 2.5 mm. As expected, the porous few layer g-C3N4 nanosheets provide rich interface which increases multiple reflection paths and enhances the conduction loss. The cooperative effects of magnetic loss, dielectric loss, and impedance matching contribute to the exceptional EMW absorption property of PFL g-C3N4/NiCo2O4 (2D/2D) heterostructure. The potential of PFL g-C3N4/NiCo2O4 in actual radar stealth is verified through radar scattering cross-section (RCS) simulation. This work paves the way for utilizing 2D/2D heterostructure as an ultra-efficient EMW absorbers.

A dual-band polarization independent dielectric metasurface-based absorber for sensing application in the visible light regime

We present a dual-band, polarization-independent dielectric terahertz absorber exhibiting near-perfect absorption and minimal reflection at frequencies of f 1 = 419 THz and f 2 = 528 THz. Using electromagnetic theory, we modeled the structure to derive the surface electric admittance and magnetic impedance of the metasurface, elucidating the conditions required for perfect absorption in terms of inverse electric and magnetic polarizabilities. The absorber features a tunable symmetrical design, facilitating precise frequency adjustment by modifying structural parameters and ensuring polarization independence for perpendicularly incident electromagnetic waves. This scalable and versatile absorber, constructed from readily available materials, is optimally suited for applications in resource detection, imaging, sensing, and medical diagnostics, attributed to its simplicity, cost-effectiveness, and high performance.

Wide-angle non-reciprocal thermal radiator based on a periodic toroidal array structure

Non-reciprocal thermal radiation is crucial for energy transfer and storage applications. However, the range of angles of incidence limits the development of non-reciprocal thermal radiation. To address this problem, we have proposed and developed a non-reciprocal thermal radiation device with wide-angle characteristics, which operates in the mid-infrared spectral range. The radiator consists of a silicon-based periodic toroidal array, a Weyl semimetal (WSM), and a metal reflective layer Ag. A strong nonreciprocity of 0.88 is observed at 9.36 μm wavelength and 41.8° angle, while a nonreciprocity of 0.87 can be sustained within the range of 36°–74°. In addition, the nonreciprocity can be maintained above 0.8 in the spectral range of 9.3 μm ∼9.4 μm. Compared with the previous single working angle, our work has dramatically broadened the angle of energy absorption, and the non-reciprocal intensity can be maintained at a high level. Through a detailed analysis of the magnetic field modulus and impedance characteristics at non-reciprocal wavelengths, we reveal that cavity resonance excitation is the core physical process of mid-infrared wide-angle non-reciprocal radiation. In addition, changing the axial vector of the WSM can lead to a redshift of the non-reciprocal wave peaks. The proposed two-dimensional mid-infrared non-reciprocal emitter can realize wide-angle domain emission at specific wavelengths, which is promising for applications in energy storage and conversion systems such as solar cells and thermophotovoltaic cells.

Boosting magnetic loss and impedance matching based on laminated structure for balancing low-/high-frequency broadband microwave absorption

Balancing low-/high-frequency broadband absorption is significantly essential for realizing ultra-wideband microwave absorption but mains challenging. In this work, laminated dielectric@magnetic FePO4/CrPO4@FeSiCr flakes have been created using facile vertical ball milling technique and subsequent phosphate passivation process. The flaky morphology provides the strong magnetic loss ability for boosting a lower-frequency microwave absorption. The dielectric@magnetic structure contributes good impedance matching and sufficient double loss mechanism for ensuring a wideband higher-frequency microwave absorption. The unique laminated structure is benefit for multi-scattering and reflection, which can balance the low-/high-frequency broadband absorption. With 6 h ball milling, FePO4/CrPO4 hybrid layer covers FeSiCr flakes deliver effective absorption bandwidth (EAB) of 1.6 GHz covering 2.4–4.0 GHz (S-band) with 3.2 mm, EAB of 3.52 GHz covering 4.40–7.92 GHz (C-band) with 1.9 mm and EAB of 8.24 GHz covering 9.36–17.6 GHz (X+Ku band) with 1.1 mm. Generally, an easy pathway is provided in this work for developing ultra-wide microwave absorbers that balance low-/high- frequencies.

Understanding Ion Dynamics in Closoborate-Type Lithium-Ion Conductors on Different Time-Scales.

The lithium-ion transport mechanism in 0.7Li(CB9H10)-0.3Li(CB11H12) complex hydride solid electrolyte was studied over a wide time-scale (ns-ms) by choosing appropriate techniques for assessing ionic motion on the desired time-scale using nuclear magnetic resonance (NMR) relaxation, AC impedance, and pulsed field gradient-NMR (PFG-NMR) measurements. The 7Li NMR line width decreased with increasing temperature, and the spin-lattice relaxation time T1 for the cation and anions showed a minimum near 303 K, indicating that the lithium ions and the anions were highly mobile. The activation energy estimated from the analysis of the NMR relaxation time matched well with the values estimated from the AC impedance and PFG-NMR. This confirms that the lithium-ion motion in 0.7Li(CB9H10)-0.3Li(CB11H12) is the same over a wide time-scale, suggesting steady Li-ion motion over a wide transport range. This understanding offers insights into strategies for designing complex hydride lithium superionic conductors.

Ultralow-content Co decoration on Ti3C2Tx MXene induced electromagnetic characteristic modulation for efficient microwave absorption

Ti3C2Tx MXene has been regarded as a promising candidate for advanced microwave absorption materials. However, the microwave absorbing performance of Ti3C2Tx MXene is suppressed by the single dielectric loss mechanism and impedance mismatch because of the high conductivity. To effectuate a good absorption capability of Ti3C2Tx MXene, this paper constructs a heterostructured Co/Ti3C2Tx hybrid by atomic layer deposition of magnetic Co nanoparticles on Ti3C2Tx nanosheets. The microstructures, magnetism, and microwave absorption behaviors of the Co/Ti3C2Tx hybrids are investigated systematically. The results show that the frequency-dependent electromagnetic parameters of the Ti3C2Tx MXene become tunable by controlling the content of Co decorations, which are conducive to both magnetic loss and impedance matching. The Co/Ti3C2Tx hybrid with ultralow Co decoration content (only 1.52 wt%) achieves the minimum reflect loss of −54.32 dB at a thin matched thickness of 1.29 mm, and the corresponding effective absorption bandwidth with reflection loss below −10 dB reaches 4.29 GHz. The atomic layer deposited magnetic metal nanostructures provides an effective strategy for preparing MXene-based hybrids which not only have high absorption efficiency but also significantly reduce the use of magnetic metals.

Facile preparation of ZIF-8/ZIF-67-derived biomass carbon composites for highly efficient electromagnetic wave absorption

Biomass absorbing materials have received increasing attention for electromagnetic wave (EMW) absorption field absorbing materials due to its low density and high dielectric loss. However, the biomass EMW absorbing materials often suffer from the insufficient magnetic loss and impedance matching. In this work, a facile ZIF-8/ZIF-67-derived biomass composites (CoZnO@BPC) was prepared for high-performance EMW absorption based on multi-component micro, nano structures metal particles and xanthoce sorbifolia bunge shells-derived biomass porous carbon (BPC). The dielectric loss and/or magnetic loss abilities of CoZnO@BPC composites were adjusted by changing the mass ratio of Zn2+ to Co2+ ions. Under the filled amount of 20 wt%, CoZnO@BPC exhibited excellent EMW absorption with the minimum reflection loss (RL) at 15.84 GHz is -50.2 dB, and the matching thickness is only 1.7 mm. By adjusting the ZIFs mass ratio, the effective absorption bandwidth (EAB) can be up to 5.92 GHz (from 12.08 GHz to 18 GHz), and the matching thickness is only 1.9 mm. The results provide a new insight for the economical and efficient preparation of lightweight and advanced microwave absorbing materials.

Topological magnetic transition and impedance modulation based on rotational deformations

Topological magnetic transition and impedance modulation based on rotational deformations

All-in-one: Multi-parameter engineering on γ-Fe2O3 for ultra-broadband microwave absorption

The functionality and property of materials are normally controlled by changing their composition, defects, morphology, lattice, crystallinity, etc. However, achieving a wide effective absorption bandwidth through multiple-parameter optimization is less reported. Simultaneously adjusting these parameters can serve as an effective control knob to increase dielectric loss, including conduction and polarization, thereby providing a broadband absorption toward radiated microwave for potential applications. Herein, magnetic γ-Fe2O3 in a two-dimensional configuration was synthesized through a molten salt process, which was further modified by Co and Al heteroatoms to facilitate more polarization processes. The reinforcement of conduction loss is achieved by increasing the crystallinity of the absorber, which facilitates the rapid transfer of free electrons and reduces scattering. Controlled alkaline etching was employed to extract a portion of the intercalated Al atoms. Henceforth, appropriate lattice distortion and numerous O vacancies are constructed, which can not only generate new polarization centers on the absorber matrix but also maintain a high crystalline structure with good conduction loss feature. In addition, the magnetic loss and impedance matching characters are optimized. As a result, the composition, structure, defects, and crystallinity of magnetic γ-Fe2O3 nanosheets have all been optimized, which enable an impressive microwave absorption performance with an effective absorption bandwidth of 7.82 GHz and a minimum reflection loss of −54.9 dB. This work explores improving the electromagnetic parameters of absorbers through collaborative regulation of multiple parameters and provides guidance for a novel and facile strategy for controlling microwave absorbers.

Proton Diffusion in Liquid 1,2,3-Triazole Studied by Incoherent Quasi-Elastic Neutron Scattering.

Improving the proton transport in polymer electrolytes impacts the performance of next-generation solid-state batteries. However, little is known about proton conductivity in nonaqueous systems due to the lack of an appropriate level of fundamental understanding. Here, we studied the proton transport in small molecules with dynamic hydrogen bonding, 1,2,3-triazole, as a model system of proton hopping in a nonaqueous environment using incoherent quasi-elastic neutron scattering. By using the jump-diffusion model, we identified the elementary jump-diffusion motion of protons at a much shorter length scale than those by nuclear magnetic resonance and impedance spectroscopy for the estimated long-range diffusion. In addition, a spatially restricted diffusive motion was observed, indicating that proton motion in 1,2,3-triazole is complex with various local correlated dynamics. These correlated dynamics will be important in elucidating the nature of the proton dynamics in nonaqueous systems.

Bioactive Ion-Based Switchable Supercapacitors

Switchable supercapacitors enable a reversible electrically driven uptake and release of bioactive ions by polarizing nanoporous carbon electrodes. In this work we demonstrate the first example of a bioactive ion-based switchable supercapacitor. Based on choline chloride and nanoporous carbons with defined porosity we unravel the mechanism of physisorption vs. electrosorption by nuclear magnetic resonance, Raman, and impedance spectroscopy. Weak physisorption leads to pronounced electrically driven electrolyte depletion enabling the release and capture of electrolyte ions in highly controllable and reversible manner. A new 4-terminal device structure is proposed, with a main capacitor and a smaller inserted detective capacitor for monitoring bioactive ions electrosorption in situ. Controlling the ion concentration in a printed switchable supercapacitor based on bioactive ions realizes switching down to 8.3% residual capacity.The exploration of electrically driven adsorption mechanisms in printable microdevices will open an avenue of manipulating bioactive ions for the further application of drug delivery, neuromodulation, or neuromorphic devices. Figure 1

Relaxation Annealing Influence on the Magnetic Properties and Magnetic Impedance of Amorphous Co-Based Wires

Abstract—The results of a study of the influence of the 2 hours relaxation annealing at a temperature of 620 K on the magnetoimpedance effect (MI) in amorphous Co66Fe4Nb2.5Si12.5B15 wires are presented. It was found that MI at low ac frequencies after heat treatment increases noticeably, while it changes slightly at high frequencies. Using magneto-impedance tomography, it is shown that this is due to the fact that the changes in magnetic properties caused by heat treatment are not the same in different regions of the wire. Thus, in the surface region with a thickness of about 2.5 μm, the magnetic permeability remains almost unchanged, but in the internal regions it increases significantly after annealing.

The Influence of Relaxation Annealing on the Magnetic Properties and Magnetic Impedance of Amorphous Co-Based Wires

The Influence of Relaxation Annealing on the Magnetic Properties and Magnetic Impedance of Amorphous Co-Based Wires

Non-invasive imaging of neural activity with magnetic detection electrical impedance tomography (MDEIT): a modelling study

Objectives. (1) Develop a computational pipeline for three-dimensional fast neural magnetic detection electrical impedance tomography (MDEIT), (2) determine whether constant current or constant voltage is preferable for MDEIT, (3) perform reconstructions of simulated neural activity in a human head model with realistic noise and compare MDEIT to EIT and (4) perform a two-dimensional study in a saline tank for MDEIT with optically pumped magnetometers (OPMs) and compare reconstruction algorithms. Approach. Forward modelling and image reconstruction were performed with a realistic model of a human head in three dimensions and at three noise levels for four perturbations representing neural activity. Images were compared using the error in the position and size of the reconstructed perturbations. Two-dimensional MDEIT was performed in a saline tank with a resistive perturbation and one OPM. Six reconstruction algorithms were compared using the error in the position and size of the reconstructed perturbations. Main results. A computational pipeline was developed in COMSOL Multiphysics, reducing the Jacobian calculation time from months to days. MDEIT reconstructed images with a lower reconstruction error than EIT with a mean difference of 7.0%, 5.5% and 11% for three noise cases representing current noise, reduced current source noise and reduced current source and magnetometer noise. A rank analysis concluded that the MDEIT Jacobian was less rank-deficient than the EIT Jacobian. Reconstructions of a phantom in a saline tank had a best reconstruction error of 13%, achieved using 0th-order Tikhonov regularisation with simulated noise-based correction. Significance. This study demonstrated that three-dimensional MDEIT for neural imaging is feasible and that MDEIT reconstructed superior images to EIT, which can be explained by the lesser rank deficiency of the MDEIT Jacobian. Reconstructions of a perturbation in a saline tank demonstrated a proof of principle for two-dimensional MDEIT with OPMs and identified the best reconstruction algorithm.

Erbium substituted baddeleyites (ErxZr(1-x)O2): Structural, ferroelectric, magnetic and electrochemical analysis for supercapacitors electrodes using walnut shells charcoal

The fabrication of ErxZr(1-x)O2 (x = 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) is carried out with solid-state method at 1200 °C temperature for 4-hrs to get the desired monoclinic structure. The structural, ferroelectric magnetic and electrochemical properties are investigated with X-ray diffractometer, ferroelectric, magnetic, cyclic voltametric, charging/discharging and electrochemical impedance respectively. The XRD and refinement parameters shows the formation of monoclinic symmetry. The low value of R-factors ensures the structural stability. The vista and diamond software are used to determine the different physical properties. The characteristic band at 665 and 721 cm−1 confirms the monoclinic identity of ZrO2 with ATR-FTIR. The SEM graphs show that the average particle size is present in 127-122 nm range. The decreased particle size is associated with the enhanced Csp due to the incease of surface-to-volume ratio. The ferroelectric analysis revealed the centrosymmetric alignment of tetrahedron sites having the 4-faces, 6 edges and 4-vertices. The magnetic analysis exposed the soft-diamagnetic feature. The high value of coercivity (Hc < Mr/2) gives the direction towards energy storage application. The CV graphs gives the good 389.8 F/g Csp which correlated with the GCD and EIS data. The highest 396.1 F/g Csp is measured using the charge/discharge curve and 309.75 F/g is calculated using the frequency-dependent EIS spectra. These high aggregates of specific capacitance values make them eligible for supercapacitors application.

Surface Crystallization and Magnetization Reversal Processes in Amorphous Microwires

The bulk-inhomogeneous crystallization of amorphous microwires of composition Fe73.8Cu1Nb3.1B9.1Si13 has been studied. An assumption was put forward about the influence of the non-uniform distribution of tensile and compressive stresses in the bulk of microwires on their crystallization. It has been established that at the initial stages of crystallization the crystallization occurs in the near-surface region of a microwire with a thickness of about 2.5 μm. It has been established that the sizes of nanocrystals in the surface region of microwire are about 10 nm. It was found that the formation of an amorphous nanocrystalline layer on the microwire surface leads to an increase in the Mr/MS ratio (ratio of remanent magnetization to saturation magnetization), which is associated with a decrease in the magnetic anisotropy due to a decrease in the stress level during heat treatment and nanocrystallization. Chemical etching of annealed microwires leads to a significant increase in the Mr/MS ratio, which is due to an increase in the relative volume of the central domain layer. The results obtained indicate the potential for creating composite amorphous-nanocrystalline structures based on microwires. In the case of microwires of Fe73.8Cu1Nb3.1B9.1Si13 composition, the predominant crystallization of the surface layer can increase the effect of the giant magnetic impedance. Such objects may have potential applications in sensorics, in particular, in magnetic field and strain sensors.

Structural, magnetic, dielectric and spectroscopic impedance analysis of magnesium iron oxide thin films synthesized by electrodeposition: Effect of preferred orientation

Magnesium iron oxide is the most valuable and versatile spinel system with reduced eddy current and dielectric losses. Spinel ferrites are electrically non-conductive. The electrodeposition is used to synthesize thin films on Cu substrate. A set of five thin films is prepared by varying the in-situ oxidation time (10 min, 15 min, 20 min, 25 min and 30 min) and a fixed deposition time of 25 min. The x-ray diffractometer XRD (phase confirmation), Scanning Electron Microscope SEM (morphological analysis), Fourier transforms infra-red spectroscope FT-IR (bond-formation), impedance analyzer (dielectric-measurements) and vibratory sample magnetometer VSM (magnetic properties) has been utilized to examine the prepared samples. All the studied samples have been found, single-phase spinel structures. XRD shows the pure phase formation of spinel MgFe2O4 at 20 min, 25 min, and 30 min. The exchange of the preferred orientation (PO) from (731) mixed phase to (533) spinel is observed. This change in preferred orientation has been caused the changes in the properties of prepared thin films. The average lattice constant, cell volume, x-ray density and crystallite size of magnesium-iron oxide were found at 8.3814 Å, 588.58 (Å)3, 3.2098 g/cm3 and 24.0392 nm respectively. In FTIR analysis of magnesium-iron oxide, two characteristic spinel bands are observed below 700 cm−1. The SEM result showed a smooth granular structure at 30 min. The normal behavior of the dielectric constant and single semicircle is observed in cole-cole plot. All the prepared thin films are ferromagnetic in nature. At 30 min, a higher dielectric constant, 20.2 (log f = 5) and 162.3 emu/cm3 saturation magnetization. The remarkable dielectric and magnetic findings are promising for using electrodeposited thin films in electronic and spintronic devices.

Polyvinylpyrrolidone induced uniform coating of nickel nanoparticles on carbon nanotubes for efficient microwave absorption

The impedance matching performance of carbon nanotubes (CNTs) can be effectively enhanced by developing a uniform magnetic impedance matching layer, which can take on critical significance in achieving the desirable microwave absorption (MA) performance. To obtain a uniform coating of Nickel (Ni) nanoparticles on CNTs, several methods have been developed (e.g., the γ-irradiation technique, electroless deposition, as well as microwave welding method). However, the intricate and complicated conditions of the above-mentioned methods limit their wide application. Therefore, controlling the distribution of Ni nanoparticles with the aid of a concise and effective method remains a great challenge. Herein, in view of the uniform dispersion effect of polyvinylpyrrolidone (PVP) on CNTs and its complexation with Ni ions, uniform coating of Ni nanoparticles on CNTs is well developed after it is introduced in the hydrothermal process. The prepared Ni/CNTs composites exhibited excellent MA performance in comparison with those of reported Ni/CNTs composites for the ideal impedance matching performance and microwave attenuation ability. When the filler content was only 15 wt%, the minimum reflection loss (RLmin) reached −39.5 dB, and the effective bandwidth (EB) with RL < -10 dB reached 5.2 GHz at the thickness of 1.15 mm. A scalable strategy of regulating the distribution of Ni nanoparticles and preparing a lightweight microwave absorber based on CNTs was developed in this study, which can serve as a vital guideline for preparing novel MA composite materials.

Millimeter-Wave Ferromagnetic Resonance of a Saturated Magnetic Transmission Line

Saturated ferrites exhibit microwave and millimeter wave absorption because they consist of nano- magnetic harmonic oscillators. The absorption frequency and line width are dictated by the strength and range of interactions between the magnetic dipoles. The forced orientation of magnetic dipoles along the magnetic bias results in Zeeman splitting in the energy levels. The incoming electromagnetic wave can excite dipoles to transition between these energy levels. In order to investigate the effects of input frequency and Gilbert damping constant on the electromagnetic properties, a magnetic transmission line model is presented for a saturated ferrite. The enhanced power loss during ferromagnetic resonance is contributed to the strong spike of longitudinal magnetic admittance and transverse magnetic impedance.

Determination of Magnetic Structures in Magnetic Microwires with Longitudinally Distributed Magnetic Anisotropy.

We studied the magnetic properties of a glass-covered amorphous microwire that was stress-annealed at temperatures distributed along the microwire length. The Sixtus-Tonks, Kerr effect microscopy and magnetic impedance techniques have been applied. There was a transformation of the magnetic structure across the zones subjected to annealing at different temperatures. The annealing temperature distribution induces the graded magnetic anisotropy in the studied sample. The variety of the surface domain structures depending on the longitudinal location has been discovered. Spiral, circular, curved, elliptic and longitudinal domain structures coexist and replace each other in the process of magnetization reversal. The analysis of the obtained results was carried out based on the calculations of the magnetic structure, assuming the distribution of internal stresses.