External Magnetization Research Articles

An alternative approach for measuring yield stress and its application in Carbopol microgel

An innovative experimental apparatus for the direct measurement of yield stress was conceived and realized. It is based on a torsion pendulum equipped with a magnetic dipole and a rotating cylinder immersed in the material to be investigated. The pendulum equilibrium state depends on the mechanical torque applied due to an external magnetic induction field, elastic reaction of the suspension wire, and shear yield stress. Experimental results are reported showing that the behavior of the pendulum rotation angle, in different equilibrium conditions, provides evidence of the yield stress presence and enables its evaluation by equilibrium equations. The dependence on time of the equilibrium approach was also studied, contributing to shed light on the relaxation effect in the transition from a fluid-like to solid-like behavior, as well as on the eventual thixotropic effects in non-Newtonian fluids. The validity of the proposed technique and related experimental apparatus was tested in aqueous Carbopol solutions, with different weight percentages. The linear procedure, combined with the effectiveness and reliability of the proposed experimental method, candidates it to be used for the study of peculiar behaviors of other yield stress complex fluid such as blood, crude waxy oils, ice slurries, and coating layer used in the food industry and also for fault sliding in geodynamics.

Investigation of the Impact of Load on the Magnetic Field Strength of the Crane by the Magnetic Metal Memory Technique.

The paper deals with the problem of applicability of the metal magnetic memory (MMM) technique in the crane structural inspection and monitoring. The MMM method does not require the external magnetization of a structure that results in reduction of downtime of maintenance operations. Measurement of the intensity of the self-magnetic leakage signal can be an alternative to other non-destructive methods used for inspection of a large crane’s structure and equipment. However, the complexity of the residual magnetization effect in the MMM technique is the problem with its application. Thus, the magnetic flux leakage behavior on the crane girder surface under different measurements and the crane’s load conditions is analyzed based on the results obtained during experiments carried out on the overhead traveling crane.

A Domain Dynamic Model Study of Magneto-impedance Sensor in the Presence of Inhomogeneous Magnetic Fields

We investigate the effect of an inhomogeneous external magnetic field and magnetization on magneto-impedance (MI) effect based on the domain dynamic model. The impedance (Z) of a thin magnetic layer under different field inhomogeneity and magnetization inhomogeneity (FIH/MIH) profiles is calculated. The MI effect determined in different frequencies shows fixed MI peak location when field and magnetization are homogeneous. However, for the cases of FIH/MIH conditions, the locations of the peaks are changed for different frequencies and layer thicknesses. The MI peaks are broadened due to the FIH profile since not all domains rotate uniformly as the field changes along the length of the layer. In the case of MIH, the values of impedance are decreased more than those of FIH (maximally about 8% at peak positions), and the MI peak positions have less shifted to higher field values (maximally about 25%) in comparison with the FIH peak positions. In the case of FIH and MIH, our calculations show the maximum relative change in the impedance peak position of about 12%. The obtained results present useful information for improving the performance of future magnetic sensors which work based on the MI effect.

Magnetic induction can control the effect of external electrical stimuli on the spiral wave

The combination of chemical, physical, electrical, and structural properties of the neurons has made them highly complex dynamical units. One of the best tools to deal with such high-level complexity is to study the neural spatiotemporal patterns. In this work, we have focused specifically on the spiral spatiotemporal pattern. Spirals make an important contribution to some of the cortical activities. However, they also may misregulate the neural activities and lead to neurological disorders such as epilepsy or attention deficit hyperactivity disorder. Here, we have studied the effect of amplitude and frequency of an external force on the dynamics of the spiral wave in one- and two-layer neural network. We have also examined the role of synaptic connections between the neurons. For each examination, three modes of zero-, low-, and high-frequency external magnetic induction are considered. In the one-layer neural network with low frequency magnetic excitation, the frequency of the stimuli overtakes the stimuli amplitude and significantly changes the dynamics of the spirals. Nonetheless, in the case of high-frequency magnetic induction, neither the amplitude nor the frequency of the electrical force have control over the existing spirals. We also have shown how the timely pattern of neural synchronization changes when the neurons are allowed to more communicate with one another. In the two-layer neural network, on the other hand, we have shown that both the amplitude and frequency of the electrical stimuli can help to control or even eliminate the spiral waves.

Effective medium properties of a ferromagnetic microwire grid

The work presented in this paper involves the analysis of effective permittivity and permeability of a ferromagnetic microwire grid consisting of an infinite number of ferromagnetic microwires. Analytical solution is obtained through satisfying the tangential boundary conditions at the surface of a reference microwire. Subsequently, the local and average fields and hence, effective permittivity and permeability are obtained within a unit cell. The analysis reported in the literature allows to calculate only and components of the effective permittivity and permeability for the case of polarization with normal incidence. Proposed analysis provides a most generalized solution for the three diagonal elements of the effective permittivity and permeability tensors for the case of arbitrary polarization with arbitrarily incident uniform plane wave. Numerical results are obtained through MATLAB to show the impact of frequency, radius of the microwires, periodicity and applied external magnetization on the effective permittivity and permeability for and polarization. A comparative analysis is also done with the numerical results available in the literature to validate the proposed method of analysis.

Attainment of high corner accuracy for thin-walled sharp-corner part by WEDM based on magnetic field-assisted method and parameter optimization

The demand for thin-walled sharp-corner parts is constantly becoming higher in aerospace, precise instruments, and micro-electro-mechanical systems (MEMS). Nonetheless, the fabrication of thin-walled sharp-corner part is a challenging work because of its poor stiffness. Wire electrical discharge machining (WEDM) is an alternative method to machine low-stiffness part due to its non-contact material removal process. However, experimental data show that there exists an inevitable deformation in the corner area of thin-walled sharp-corner part. The goal of this paper is to achieve high corner accuracy for thin-walled sharp-corner part based on magnetic-assisted approach and parameter optimization. Firstly, a coupled magnetic-mechanical model is established to analyze the effect of the external magnetic field on the corner deformation. It can be found that the external magnetic field can effectively improve the magnetic field distribution and decrease the corner deformation. There is optimal external magnetic induction intensity between 0.2 and 0.3 T for smaller corner deformation. Then, the results of verification experiment indicate that the coupled magnetic-mechanical model is of high feasibility and reliability. In addition, a set of Taguchi experiment is implemented to investigate the influences of process parameters on the corner deformation. It can be obtained that corner deformation rises up with the increase of pulse on time and discharge peak current, and reduces along with pulse-off time. Furthermore, the optimal process parameter combination from the range analysis method can reduce corner deformation from 100 to 34.3 μm.

Immobilization of mobile and bioavailable phosphorus in sediments using lanthanum hydroxide and magnetite/lanthanum hydroxide composite as amendments

This work prepared lanthanum hydroxide (La-OH) and magnetite/lanthanum hydroxide composite (Mag-La-OH), and then La-OH and Mag-La-OH were used as sediment amendments to immobilize phosphorus (P) in sediments. The immobilization efficiency of mobile P (MobP) and bioavailable P (BIO-P) in sediments by La-OH and Mag-La-OH was investigated. Results showed that the addition of La-OH into sediment resulted in the transformation of loosely adsorbed P (LA-P) and redox sensitive P (RS-P) to sodium hydroxide extractable P (OH-P) and hydrochloride extractable P (HP) in the sediment, while the addition of Mag-La-OH into sediment led to the transformation of LA-P, RS-P and HP to OH-P and residual P (RESP) in the sediment. Both La-OH and Mag-La-OH can effectively immobilize Mob-P (LA-P + RS-P) in sediments, but La-OH had a higher Mob-P immobilization capacity than Mag-La-OH. The amendment of sediments with La-OH and Mag-La-OH both can reduce the amounts of different types of BIO-P including water soluble P (WA-P), algal available P (AL-P) and Fe oxide-paper extractable P (FE-P) in the sediments, and La-OH had a higher BIO-P immobilization capacity than Mag-La-OH. The immobilization of Mob-P in sediments by Mag-La-OH could be described by the equation: W = 0.333 × (∆Mob-P)-14.4, where ∆Mob-P (mg/kg) is the amount of Mob-P bounded in sediments and W (%) is the Mag-La-OH dosage. The immobilization of FE-P in sediments by Mag-La-OH could be described by the equation: W = 0.380 × (∆FE-P) + 1.14, where ∆FE-P is the amount of FE-P bounded in sediments. Considering that Mag-La-OH can be retrieved from the water bodies under the action of external magnetization fields after its application, Mag-La-OH could have high potential to be used as an amendment for the immobilization of Mob-P and BIO-P in sediments.

Detecting the propped fracture by injection of magnetic proppant during fracturing

Hydraulic fracturing is key to enhancing the productivity of shale and tight hydrocarbon reservoirs, as well as geothermal resources from hot dry rock. Assessing the range and efficiency of hydraulic fracturing is very important for onsite fracturing operations and decision making on subsequent fracturing plans and well-pattern deployment. The idea of injecting fluid mixed with magnetic material into a formation to detect subterranean structure has been considered for a long time. The detectability of the characteristics of propped fractures using magnetic field measurement is discussed and evaluated with an analytical model. The magnetic proppants synthesized with superparamagnetic nanoparticles should be “silent” during injection and could be activated by an external current. By measuring the magnetic field before and after the fracture was created and the magnetic proppants were magnetized, the magnetic anomalies can be obtained. The result indicates that the magnetic field caused by a fracture filled with magnetic proppants is very weak, so that magnetometers with higher precision and resolution should be used to capture such subtle signal. The higher susceptibility contrast of the magnetic nanoparticles is, the stronger external magnetic induction field could be detected. It is suggested that the superparamagnetic nanomaterial with effective magnetic susceptibility contrast of greater than 0.4–0.5 should be used for fracture monitoring in deep wells. To infer the fracture characteristics with the magnetic anomaly, the ground and adjacent wells’ monitoring practices are recommended.

Spontaneous Electromagnetic Induction Modulating the Neuronal Dynamical Response

Spontaneous electromagnetic induction originating from neuronal electrical activity is believed to reflect the memory ability in the neural system and significantly modulates neural information transmission, but its fundamental effect on the neuronal dynamic properties is still not well understood. In this paper, we use a memristor to couple neuronal electrical activity and magnetic fields and study how the spontaneous electromagnetic induction modulates the neuronal dynamical response to external stimulation. It is found that the negative feedback of electromagnetic induction on the neuron significantly reduces the dynamical response range, decreases the oscillation amplitude and induces a higher firing frequency. Meanwhile, the memory effect on electromagnetic induction can induce two kinds of bistability, including the coexistence of a stable limit cycle and a fixed point, and the coexistence of two stable limit cycles. Furthermore, high electric driving for electromagnetic induction produces complex firing patterns with single, double and multiple frequencies. Our results not only further confirm the efficacy of spontaneous electromagnetic induction in modulating the neuronal dynamical properties but also provide insights into the possibilities of choosing suitable parameter spaces in studying the effects of external magnetic induction on brain functions.

Atomic Scale Evidence of the Switching Mechanism in a Photomagnetic CoFe Dinuclear Prussian Blue Analogue.

Molecular complexes based on Prussian Blue analogues have recently attracted considerable interest for their unique bistable properties combined to ultimately reduced dimensions. Here, we investigate the first dinuclear FeCo complex exhibiting both thermal and photomagnetic bistability in the solid state. Through an experimental and theoretical approach combining local techniques-X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD), and ligand field multiplet calculations-we were able to evidence the changes occurring at the atomic scale in the electronic and magnetic properties. The spectroscopic studies were able to fully support at the atomic level the following conclusions: (i) the 300 K phase and the light-induced excited state at 4 K are both built from FeLSIII-CoHSII paramagnetic pairs with no apparent reorganization of the local structure, (ii) the 100 K phase is composed of FeLSII-CoLSIII diamagnetic pairs, and (iii) the light-induced excited state is fully relaxed at an average temperature of ≈50 K. In the paramagnetic phase at 2 K, XAS and XMCD reveal that both Fe and Co ions exhibit a rather large orbital magnetic moment (0.65 μB and 0.46 μB, respectively, under an external magnetic induction of 6.5 T), but it was not possible to detect a magnetic interaction between spin centers above 2 K.

Direct-Current and Alternate-Decay-Current Hybrid Integrative Power Supplies Design Applied to DC Bias Treatment

This paper proposes a novel kind of direct-current and alternate-decay-current hybrid integrative magnetization and demagnetization power supplies applied to transformer dc bias treatment based on a nanocomposite magnetic material. First, according to the single-phase transformer structure, one dc bias magnetic compensation mechanism was provided. The dc bias flux in the transformer main core could be eliminated directionally by utilizing the material remanence. Second, for the rapid response characteristic of the magnetic material to an external magnetic field, one positive and negative dc magnetization superimposed decaying ac demagnetization hybrid integrative power supplies based on single-phase rectifier circuit and inverter circuit was designed. In order to accurately control the magnetic field strength by which a good de/-magnetization effect could be achieved, this paper adopts the double-loop control technology of the magnetic field strength and magnetizing current for the nanocomposite magnetic state adjustment. Finally, two 10 kVA transformers and the experiment module of the hybrid integrative power supplies were manufactured and built. Experimental results showed that the integrated power supplies have good de/-magnetization effect and practicability, proving the validity and feasibility of the proposed scheme.

Reversible and magnetically unassisted voltage-driven switching of magnetization in FeRh/PMN-PT

Reversible control of magnetization by electric fields without assistance from a subsidiary magnetic field or electric current could help reduce the power consumption in spintronic devices. When increasing temperature above room temperature, FeRh displays an uncommon antiferromagnetic to ferromagnetic phase transition linked to a unit cell volume expansion. Thus, using the strain exerted by an adjacent piezoelectric layer, the relative amount of antiferromagnetic and ferromagnetic regions can be tuned by an electric field applied to the piezoelectric material. Indeed, large variations in the saturation magnetization have been observed when straining FeRh films grown on suitable piezoelectric substrates. In view of its applications, the variations in the remanent magnetization rather than those of the saturation magnetization are the most relevant. Here, we show that in the absence of any bias external magnetic field, permanent and reversible magnetization changes as high as 34% can be induced by an electric field, which remain after this has been zeroed. Bulk and local magnetoelectric characterization reveals that the fundamental reason for the large magnetoelectric response observed at remanence is the expansion (rather than the nucleation) of ferromagnetic nanoregions.

Competing effects of Hund’s splitting and symmetry-breaking perturbations on electronic order in Pb1−xSnxTe

We study the effect of a uniform external magnetization on p-wave superconductivity on the (001) surface of the crystalline topological insulator(TCI) Pb$_{1-x}$Sn$_{x}$Te. It was shown by us in an earlier work that a chiral p-wave finite momentum pairing (FFLO) state can be stabilized in this system in the presence of weak repulsive interparticle interactions. In particular, the superconducting instability is very sensitive to the Hund's interaction in the multiorbital TCI, and no instabilities are found to be possible for the "wrong" sign of the Hund's splitting. Here we show that for a finite Hund's splitting of interactions, a significant value of the external magnetization is needed to degrade the surface superconductivity, while in the absence of the Hund's interaction, an arbitrarily small external magnetization can destroy the superconductivity. This implies that multiorbital effects in this system play an important role in stabilizing electronic order on the surface.

DC vacuum breakdown in an external magnetic field

The subject of the present theoretical and experimental investigations is the effect of the external magnetic field induction on dark current and a possibility of breakdown. The generalization of the Fowler–Nordheim equation makes it possible to take into account the influence of a magnetic field parallel to the cathode surface on the field emission current. The reduction in the breakdown voltage due to the increment in electron-impact ionization was theoretical predicted. Experimentally shown that the presence of a magnetic field about a tenth as a large as the cutoff magnetic field (Hull, 1921) reduces the breakdown voltage by 10% to 20% for practically all cathodes no matter what their surface treatment.

Rashba-driven anomalous Nernst conductivity of high spin-orbit-coupled lead chalcogenide films

The presence of a finite Berry curvature $\left(\Omega\left(k\right)\right)$ leads to anomalous thermal effects. In this letter, we compute the coefficients for the anomalous Nernst effect $\left(ANE\right) $ and its spin analogue, the spin Nernst effect $\left(SNE\right)$ in lead chalcogenide (\textit{PbX}; \textit{X} = S, Se, Te) films. The narrow gapped \textit{PbX} films with a large spin-orbit coupling (\textit{soc}) offer a significant Rashba interaction that gives rise to $ \Omega\left(k\right) $ and the attendant anomalous thermal behaviour. In presence of a temperature gradient, the $ ANE $ and $ SNE $ establish a thermal and spin current and are characterized by their respective coefficients which acquire higher values for a stronger Rashba interaction. We further show that an extrinsic \textit{soc} generated by an in-plane electric field offers a gate-like mechanism to control (and turn-off) the anomalous thermal currents. Finally, we conclude by deriving the efficiency of an $ ANE $-driven low-temperature Carnot heat engine and demonstrate that it can be gainfully optimized in systems with a robust intrinsic \textit{soc} resulting in low carrier effective masses.

Taking control of initiated propagating wave in a neuronal network using magnetic radiation

The effect of magnetic radiation is essential to be studied due to its favorable or unfavorable influences especially when it comes to biological systems. In this study, some effects of an external time-varying magnetic induction on the formation of spatiotemporal patterns in a model of excitable tissue are investigated. We have designed a two-dimensional neuronal network, in which the local dynamics of the neurons are governed by the four-variable magnetic Hindmarsh–Rose (HR) neuronal model. Besides, each neuron is set to be in chaotic regime. We have examined some values of the bifurcation parameters, namely the frequency and the amplitude of the external magnetic radiation. The resulting evolutionary spatiotemporal patterns have showed that an extremely low frequency provides the tissue more opportunity to support propagation process, while low frequency confines the evolution of the wave fronts. Moreover, higher amplitude of the sinusoidal radiation caused the wave propagation be impeded by an inherent obstacle that could limit the ultimate radius of the propagated wave. The resulting collective response of the designed neuronal network is represented in snapshots and the time series of a sampled neuron are plotted, as well.

Elimination of spiral waves in excitable media by magnetic induction

The formation of spiral waves in excitable media is a fascinating example of the beauty of nonlinear dynamics in spatiotemporal systems. Apart from the beauty of the patterns, the subject also has many practical application. For example, the emergence of spiral waves in cardiac tissue can lead to arrhythmias. Cortical spiral waves are also involved in epileptic seizures. Motivated by this, we here study the effects of magnetic induction on the formation of spiral waves in excitable media. An external sinusoidal magnetic induction with different amplitudes and angular frequencies is applied in order to study whether spiral waves could be eliminated. We use a network of coupled neurons as a model for the excitable medium. The four-variable magnetic Hindmarsh–Rose model is used for the local dynamics of each isolated neuron. The distribution of the cell membrane potential over time, affected by magnetic induction, is determined and the results are depicted as snapshots of the 2D network. Our research reveals that the continuance of rotating spiral seeds is impaired by high-amplitude magnetic induction. Moreover, we show that low-frequency induction is not capable of breaking the reorganizing rhythm of the spiral seeds, while much higher frequencies can be too fast to overcome this special rhythm.

Bias field tunable magnetic configuration and magnetization dynamics in Ni80Fe20 nano-cross structures with varying arm length

Ferromagnetic nano-cross structures promise exotic static magnetic configurations and very rich and tunable magnetization dynamics leading towards potential applications in magnetic logic and communication devices. Here, we report an experimental study of external magnetic field tunable static magnetic configurations and magnetization dynamics in Ni80Fe20 nano-cross structures with varying arm lengths (L). Broadband ferromagnetic resonance measurements showed a strong variation in the number of spin-wave (SW) modes and mode frequencies (f) with bias field magnitude (H). Simulated static magnetic configurations and SW mode profiles explain the rich variation of the SW spectra, including mode softening, mode crossover, mode splitting, and mode merging. Such variation of SW spectra is further modified by the size of the nano-cross. Remarkably, with decreasing arm length of nano-cross structures, the onion magnetization ground state becomes more stable. Calculated magnetostatic field distributions support the above observations and revealed the non-collective nature of the dynamics in closely packed nano-cross structures. The latter is useful for their possible applications in magnetic storage and memory devices.

Multistable current states in high-temperature superconducting composites

Conditions for current instabilities that arise in high-temperature superconducting composites with essentially nonlinear dependences of the critical current densities and resistivity on the temperature and magnetic induction have been studied. The analysis has been conducted in terms of zero-dimensional models, which has made it possible to formulate general physical mechanisms behind the formation of currents states in superconducting composites according to the external magnetic field induction, cooling conditions, and the properties of the superconductor and cladding. The possible existence of current and temperature stable steps, as well as stable steps of the electric field strength, in the absence of the superconducting–normal transition, has been demonstrated. Reasons for instabilities under multistable current states have been discussed.

Magnetic field assisted μ-solid phase extraction of anti-inflammatory and loop diuretic drugs by modified polybutylene terephthalate nanofibers

A magnetic nanocomposite consisting of nanoparticles–polybutylene terephthalate (MNPs–PBT) was electrospun and used as an extracting medium for an on-line μ-solid phase extraction (μ–SPE)–high performance liquid chromatography (HPLC) set–up with an ultraviolet (UV) detection system. Due to the magnetic property of the prepared nanofibers, the whole extraction procedure was implemented under an external magnetic field to enhance the extraction efficiencies. The developed method along with the synthesized nanocomposite were found to be appropriate for the determination of trace levels of selected drugs including furosemide, naproxen, diclofenac and clobetasol propionate in the urine sample. The prepared MNPs-PBT electrospun nanocomposite was characterized using the scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX) and Fourier transform infrared (FT–IR) spectroscopy. The prepared magnetic fibers showed high porosity, which was another driving force for the extraction efficiency enhancement. Major parameters affecting the extraction efficiency of the selected drugs were optimized. The limits of detections (LOD) of the studied drugs were in the range of 0.4–1.6 μg L−1 and the limits of quantification (LOQ) were 1–4 μg L−1 under the optimized conditions. Relative standard deviation (RSD%) for three replicates at three concentration levels of 6, 100 and 400 μg L−1 were 5.9–8.0% while acceptable linear range with two orders of magnitude was obtained (R2 = 0.99). The method was validated by the determination of the selected drugs in urine samples and the results indicated that this method has sufficient potential for enrichment and determination of the desired drugs in the urine sample. The relative recovery values were found to be in the range of 78–91%. Implementing the developed on–line μ–SPE method under the external magnetic field induction, led to higher extraction efficiencies for the selected drugs with various diamagnetic properties.