Magnetic Field Research Articles

Room‐temperature Magnetocapacitance Spanning 97K Hysteresis in Molecular Material

AbstractMagnetic capacitor, as a new type of device, has broad application prospects in fields such as magnetic field sensing, magnetic storage, magnetic field control, power electronics and so on. Traditional magnetic capacitors are mostly assembled by magnetic and capacitive materials. Magnetic capacitor made of a single material with intrinsic properties is very rare. This intrinsic property is magnetocapacitance (MC). The studies on MC effect have mainly focused on metal oxides so far. No study was reported in molecular materials. Herein, two complexes: (CETAB)2[CuCl4] (1) and (CETAB)2[CuBr4] (2) (CETAB=(2‐chloroethyl)trimethylammonium) are reported. There exist strong H−Br and Br−Br interactions and other weak interactions in complex 2, so the phase transition energy barrier is high, resulting in the widest thermal hysteresis loop on a molecular level to date. Furthermore, complexes 1 and 2 show large MC parameters of 0.247 and 1.614, respectively, which is the first time to observe MC effect in molecular material.

Behavior of plasma parameters under mirror and cusp magnetic fields in DC glow discharge – a numerical study

Abstract The plasma parameters in DC glow discharge can easily be controlled by externally applied magnetic field without disturbing internal / built-in process parameters. Though several works have been carried out to study the influence of the magnetic field at different configurations on the plasma parameters, a complete understanding on the behaviour of the plasma discharge under the mirror and cusp fields could not be achieved. Further studies on the same are needed to improve the efficiency of the DC glow discharge system for existing applications and to find the new applications. In this work, a 2D axis-symmetric non-equilibrium plasma model with drift-diffusion approach is developed to study the characteristics of the plasma in DC glow discharge through various plasma parameters under mirror and cusp fields. The effects of current and position of magnetic coils on electric potential, ionization rate, electron temperature and electron number density are predicted and discussed. The distribution of electron number density at various coil currents and positions under both mirror and cusp fields are presented and the operating conditions favorable for applications in surface modification are suggested.

Evaluation of Low Frequency Electrical and Magnetic Fields in a Electrical Transmission Substation

Evaluation of Low Frequency Electrical and Magnetic Fields in a Electrical Transmission Substation

Efficient Analysis of Noise Induced in Low-Voltage Installations Placed Inside Buildings with Lightning Protection Systems

This paper describes an efficient approach to the broadband analysis of lightning protection systems (LPSs) using the method of moments (MoM) implemented in the frequency domain. The adaptive frequency sampling (AFS) algorithm, based on a rational interpolation of the relevant observable (e.g., voltage, current, electric or magnetic field) which describes the properties of the LPS, is employed to reduce the number of samples computed by the full-wave MoM. This improvement is achieved by the quick comparison of two interpolants with the use of the Stöer–Bulirsch algorithm, which provides the frequency location of the next MoM samples for computations. This algorithm allows for the efficient localization of resonant frequencies while reducing the number of samples computed over the entire frequency range. In the instances when the induced noise is determined in low-voltage installations protected by various types of LPSs, reductions in computational overhead equal to 47.9× and 72.1× in broadband LPS simulations are obtained. Hence, the proposed approach allows for a significant reduction in computational overhead in comparison to standard, uniformly sampled simulations.

Cattaneo‐Christov model for cross nanofluid with Soret and Dufour effects under endothermic/exothermic reactions: a modified Buongiorno tetra‐hybrid nanofluid approach

AbstractThe previous researchers used a slightly different version of the Buongiorno hybrid nanofluid (BHNF) concept. In the existing research, there is not a single effort that was undertaken to explore the effect that tetra hybrid nanoparticles (tethnf) implanted with the BHNF model have on liquid movement that is then exposed to an elastic sheet. This endeavor focuses on researching the implication of a modified Buongiorno tetra hybrid cross nanofluid concept on magnetized radiative cross nanofluid transport, along with impacts such as Cattaneo–Christov heat flux and Cattaneo–Christov mass flux, variable thermal conductivity, diffusion‐thermo and thermo‐diffusion effects, and endothermic/exothermic type chain reactions. This approach integrates both Buongiorno and tethnf. By inserting similar variables, the controlling model partial differential equations have been transformed into dimensionless Ordinary differential equations. These equations are then treated computationally with the help of the Lobatto III A technique. The MATLAB computer program is used to produce simulation solutions, as well as the findings, which are displayed in the form of graphs and tables. Based on the results that have been gathered, it was discovered that the speed of heat delivery increases when there is an increase in the speed of an endothermic reaction. When the Dufour and thermal relaxation factors are increased, the speed at which heat is transmitted also increases. The fluid viscosity becomes more pronounced as a result of an increase in the viscosity index n, the Weissenberg number We, and the magnetic field M, all of which contribute to a reduction in the velocity distribution. A progressive change in the radiation parameters Rd, Dufour effect, and thermal conductivity which magnifies Nusselt number causes an increase in the heat delivery rate, which in turn amplifies Nusselt number.

Uncertainty analysis of MHD oscillatory flow of ternary nanofluids through a diverging channel: a comparative study of nanofluid composites

Purpose This study aims to investigate the heat and mass transfer characteristics of a temperature-sensitive ternary nanofluid in a porous medium with magnetic field and the Soret–Dufour effect through a tapered asymmetric channel. The ternary nanofluid consists of Boron Nitride Nanotubes (BNNT), silver (Ag) and copper (Cu) nanoparticles, with a focus on understanding the thermal behaviour and performance across mono, hybrid and tri-hybrid nanofluids. This paper also examines the thermal behaviour of MHD oscillatory nanofluid flow and carries out an uncertainty analysis of the model using the Taguchi method. Design/methodology/approach The governing equations for this system are transformed into coupled linear partial differential equations using non-similarity transformations and solved numerically with the Crank–Nicolson scheme. The impact of temperature sensitivity at three distinct temperatures (5°C, 20°C and 60°C) is incorporated to analyse variations in viscosity and Prandtl number. The study also examines the combined effects of Soret–Dufour numbers and thermal radiation on heat and mass transfer within the nanofluid. Findings The results demonstrate that the inclusion of BNNT, Ag and Cu nanoparticles significantly enhances heat and mass transfer rate, with copper nanoparticles showing superior performance in terms of skin friction and heat transfer rates. The Soret and Dufour effects play critical roles in modulating heat and mass diffusion within tri-hybrid nanofluids. The study reveals that temperature sensitivity alters heat and mass transfer characteristics depending on the temperature range, with pronounced variations at elevated temperatures. The influence of thermal radiation and the Peclet number is found to significantly impact temperature distribution and overall heat transfer performance within the asymmetric channel. Originality/value To the best of the authors’ knowledge, this study is the first to analyse the heat and mass diffusion in a ternary nanofluid composed of BNNT, Ag and Cu nanoparticles, considering porous media, oscillatory flow and thermal radiation within a tapered asymmetric channel. The research extends to a novel examination of temperature sensitivity in mono, hybrid and tri-hybrid nanofluids at varying temperature gradients. Furthermore, a comparative analysis of skin friction and heat transfer rates between copper, alumina and ferro composites is presented for optimising the nanofluid performance.

Finite-field Cholesky decomposed coupled-cluster techniques (ff-CD-CC): theory and application to pressure broadening of Mg by a He atmosphere and a strong magnetic field.

For the interpretation of spectra of magnetic stellar objects such as magnetic white dwarfs (WDs), highly accurate quantum chemical predictions for atoms and molecules in finite magnetic field are required. Especially the accurate description of electronically excited states and their properties requires established methods such as those from coupled-cluster (CC) theory. However, respective calculations are computationally challenging even for medium-sized systems. Cholesky decomposition (CD) techniques may be used to alleviate memory bottlenecks. In finite magnetic field computations, the latter are increased due to the reduction of permutational symmetry within the electron-repulsion-integrals (ERIs) as well as the need for complex-valued data types. CD enables a memory-efficient, approximate description of the ERIs with rigorous error control and thus the treatment of larger systems at the CC level becomes feasible. In order to treat molecules in a finite magnetic field, we present in this work the working equations of the left and right-hand side equations for finite field (ff)-EOM-CD-CCSD for various EOM flavours as well as for the approximate ff-EOM-CD-CC2 method. The methods are applied to the study of the modification of the spectral lines of a magnesium transition by a helium atmosphere that can be found on magnetic WD stars.

Temperature-Sensitive Magnetic Resonance Probes: Leveraging Hyperpolarized Pyridine-2-Carbaldehyde and SABRE for Real-Time Temperature Sensing.

In this study, we developed a novel approach for real-time, temperature-sensitive nuclear magnetic resonance (NMR) measurements using signal amplification by reversible exchange (SABRE). We discovered that pyridine-2-carbaldehyde (A) exhibits different behavior depending on temperature, showing high hyperpolarization efficiency. In contrast, its reversible reaction product, the hemiacetal form (A'), is not affected by temperature. Exploiting this difference, we achieved a reliable polarization enhancement ratio without internal standard materials, even at low concentrations. Our method overcomes challenges associated with SABRE for 2-functionalized pyridines, enabling direct temperature monitoring in real-time NMR studies. We successfully applied it to monitor temperatures in solutions containing SABRE-inactive compounds like caffeine. Furthermore, we demonstrated its efficacy using a 60 MHz benchtop NMR spectrometer, validating its potential in challenging environments where conventional techniques may be limited. This technique shows promise for influencing the magnetic resonance field, potentially facilitating more accurate real-time analyses of molecular reactions and structures. Future research will focus on adapting this method for biological settings, aiming to stimulate advancements in NMR and magnetic resonance imaging (MRI) applications.

Thermodynamics and entropic inference of nanoscale magnetic structures in Gd.

A bulk gadolinium (Gd) single crystal exhibits virtually zero remnant magnetization, a common trait among soft uniaxial ferromagnets. This characteristic is reflected in our magnetometry data showing virtually hysteresis free isothermal magnetization loops with large saturation magnetization. The absence of hysteresis allows to model the measured easy axis magnetization as a function of temperature and applied magnetic field, rather than a relation, which permits the application of Maxwell relations from equilibrium thermodynamics. Demagnetization effects broaden the isothermal first-order transition from negative to positive magnetization. By analyzing magnetization data within the coexistence regime, we deduce the isothermal entropy change and the field-induced heat capacity change. Comparing the numerically inferred heat capacity with relaxation calorimetric data confirms the applicability of the Maxwell relation. Analysis of the entropy in the mixed phase region suggests the presence of hitherto unresolved nanoscale magnetic structures in the demagnetized state of Gd. To support this prediction, Monte Carlo simulations of a 3D Ising model with dipolar interactions are performed. Analyzing the cluster size statistics and magnetization from the model provides strong qualitative support of our analytic approach.

Alfvén waves in the solar corona: resonance velocity, damping length, and charged particles acceleration by kinetic Alfvén waves.

Recent advances in heliospheric exploration spurred by NASA's Parker Solar Probe (PSP) mission require a deeper understanding of the intricate dynamics of the solar corona and wind. This study provides a detailed examination of kinetic Alfvén waves (KAWs) within the RSun range, a region only briefly explored in future PSP passages. Employing the framework of kinetic plasma theory and incorporating a non-thermal Cairns velocity distribution, we investigate the impact of the non-thermal index parameter on the resultant resonance velocity . The results reveal a notable change in the distance (RSun) over which the particles transport energy and the magnitude of resonance velocity for . We also derive the perpendicular resonance velocity and the group velocity expressions of particles and KAWs, respectively. We find that and the normalized group velocity are significantly influenced by . In contrast to the resonance speed and group velocity, the damping length of KAWs is evaluated for different parameters. We find that KAWs experience accelerated damping and exhibit an increased damping length for . We evaluate KAWs by the influence of the magnetic field, variation in height relative to the solar radius RSun, and the electron-to-ion temperature ratio . Collectively, these findings illustrate that KAWs not only are important for heating processes but also accelerate charged particles across considerable distances within the solar corona and solar wind regions. The analytical insights gleaned from this study find practical application in understanding wave phenomena in the solar and heliospheric regimes, particularly exploring the role of non-thermal particles in observed heating processes.

A numerical comparison of Gd, Pr0.65Sr0.35MnO3 and single LaFeCoSi, for use in room temperature magnetic cooling applications

Abstract One of the most significant scientific difficulties to achieving excellent performance for room-temperature magnetic cooling devices is finding suitable magnetocaloric refrigerants. To contribute to this research field, three kinds of magnetocaloric materials (Gd, Pr0.65Sr0.35MnO3 and single LaFeCoSi) in the same conditions (Curie temperature, applied magnetic field) have been considered to evaluate their potential in the magnetic refrigeration application using a 1D-AMRR (Active-Magnetic-Refrigeration-Regenerator) cycle with a parallel plate regenerator. In this way, four cooling performance parameters were investigated, namely the temperature span, the cooling power, the exergy, and the coefficient of performance. The temperature span was found to be 11.79K for Gd , 8K for LaFeCoSi and 4.47 K for Pr0.65Sr0.35MnO3. The obtained numerical results reveal that the Gd-based AMR system displays a higher efficiency, while the Pr0.65Sr0.35MnO3-based AMR system exhibits a smaller one. The magnetocaloric effect (MCE) in the magnetic refrigerants was considered to explain the result obtained and can be considered as one of the main factors to enhance the magnetic refrigeration performance.

Application of machine learning for detecting and tracking turbulent structures in plasma fusion devices using ultra fast imaging.

This study explores the application of machine learning techniques for detecting and tracking plasma filaments around the boundary of magnetically confined tokamak plasmas. Plasma filaments, also called blobs, are responsible for enhanced turbulent transport across magnetic field lines, and their accurate characterization is crucial for optimizing the performance of magnetic fusion devices. We present a novel approach that combines machine learning methods applied to data obtained from ultra-fast cameras, including YOLO (You Only Look Once) for object detection, semantic segmentation, and specific tracking methods. This approach enables fast and accurate detection and tracking of filaments while overcoming the limitations of conventional methods, which are time-consuming and prone to human subjectivity. A significant advance in our study lies in the development of a method for automatically labeling a large batch of data, which greatly facilitates the training of supervised machine learning algorithms. Using these techniques, we obtained promising results demonstrating a significant improvement over conventional tracking methods, achieving a detection accuracy of up to 98.8%, while reducing the inference time per frame by 15% to 31% compared to conventional Kalman filter tracking. These results open up new perspectives for investigating turbulent phenomena in tokamaks, and could have important implications for the development of controlled nuclear fusion.

Analyzing Pulse Compression Performance and Image Quality Metrics of Different Excitations in MAET With Magnetic Field Measurements.

This study investigates the pulse compression technique to improve the performance of magneto-acousto-electrical tomography (MAET) with magnetic field measurements through numerical studies. Emphasizing the effects of specific coil configuration on MAET measurements, the study conducts evaluations using a linear phased array (LPA) transducer and numerical breast models with tumor inclusion. It provides feasibility and a detailed comparative analysis of various excitations, including linear frequency modulated (LFM), Barker code, and Golay code excitations in MAET. To simulate experimental conditions, additive White Gaussian noise is added to the MAET signal detected by the receiver coils. The results obtained from the LPA steering angle at 0° and the reconstructed B-mode MAET images using the pulse compression technique lead to improvements compared with conventional single-cycle excitation. The computed mean signal-to-noise ratio (SNR) improvements for LFM, Barker code, and Golay code excitations in B-mode MAET images for 10,000 iterations are 7.42, 8.36, and 8.44 dB, respectively, compared with single-cycle excitation. Similarly, the mean contrast-to-noise ratio (CNR) improvements for these excitations in B-mode MAET images are 1.43, 1.63, and 1.9 dB, respectively. The results demonstrate that Golay code is superior in CNR and image quality metrics, while Golay and Barker codes have comparable SNR and outperform LFM. The research shows that the coil configuration significantly impacts tumor detection. With Golay code excitation, detecting a tumor as small as 5 mm × 2 mm at a depth of 33 mm with an SNR of 6.38 dB is possible, achieving an axial resolution of 2 mm.

Theoretical Study of Position-Dependent Mass Particle in Cosmic String Space-Time and External Magnetic Field

In this work, we discuss the case of a non-relativistic quantum particle in the cosmic string space-time under the influence of the presence of external magnetic and exponential potential. It’s shown with the help of the Laplace transform method the second-order differential equation of the Schrodinger equation is solvable where it is reduced to a first-order differential equation. We obtain the eigenfunction and the non-relativistic energy spectrum. In addition, these results may be useful in the future study of thermodynamic, optic, and magnetic properties of the atomic interaction of a system particle. Keywords: Schrodinger equation; Laplace transform method; Position dependent mass; External magnetic field; Cosmic string

Artificial intelligence neural network and fuzzy modelling of unsteady Sisko trihybrid nanofluids for cancer therapy with entropy insights.

The main objective of the current endeavor is to monitor hypothetical processes utilizing a Sisko tri-hybrid fluid over a rotating disk with entropy generation suspended in Darcy-Forchheimer porous medium. Electro Magneto Hydro Dynamics (EMHD), non-linear thermal radiation and exponential and thermal- space dependent heat source/sink coefficients are considered with the intent of conceiving an Runge-Kutta-Fehlberg method with shooting procedures integrated with a combination of an Adaptive Neuro-Fuzzy Inference System (ANFIS) and Reptile Search Algorithm (RSA). Then, ANFIS-RSA, is used to predict the Nusselt number, skin friction co-efficient in radial and tangential velocities. Reliable self-similarity variables have reduced a non-linear partial differential set of equations into an ordinary differential equation. According to the empirical evidence, Sisko fluid parameter rises the radial velocity whereas for magnetic field and Darcy-Forchheimer the azimuthal and axial velocities visualizations decreasing trend, respectively. The entropy generation and Bejan number rises for electric and radiation effects. Also, ANFIS-RSA indicates that the model attained a high level of precision in terms of radial velocity (98.13%), tangential velocity (98.18%) and Nusselt number (98.91%). Thus, the longer rendering of the nanoparticles used here might, makes them potentially helpful for regulating the therapeutic impact in the management and treatment of cancer.

Study on the Properties and Mechanism of m‐FACs/f‐Fe3O4/Epoxy Wear‐Resistant Magnetic Coating

ABSTRACTIn view of the wear problem of key parts of magnetic fluid seal device, epoxy resin (EP) composite coatings reinforced with Fe3O4 and fly ash cenospheres (FACs) were fabricated successfully. The structural and morphological features of the fillers and the composite coatings were characterized by Fourier transform infrared and scanning electron microscopy. CFT‐I material surface performance comprehensive tester was used to investigate the tribological behaviors of the as‐prepared composite coatings. Vibrating sample magnetometer was used to investigate the coatings' magnetic property. The formation mechanism of the composite coating was analyzed by the infrared spectrum results combined with molecular dynamics simulations. The results demonstrated that adding a certain amount of double fillers will have a synergistic effect, and its mechanical properties are better than those of single fillers. The tribological property of the m‐FACs/f‐Fe3O4/EP composite coatings was optimal under magnetic fluid friction, which is about an order of magnitude lower than the wear rate under dry friction. The saturation magnetization of the m‐FACs/f‐Fe3O4/EP composite coating is 2.77 emu/g, and the magnetic susceptibility reaches 4.64 × 10−4 m3/kg. Therefore, the m‐FACs/f‐Fe3O4/EP composite coating will be expected to solve the wear problem of equipment components in complex environments of magnetic field and friction.

Unveiling key factors in solar eruptions leading to the solar superstorm in 2024 May

NOAA active region (AR) 13664/8 produced the most intense geomagnetic effects since the Halloween event of 2003. The resulting extreme solar storm is thought to be the consequence of multiple interacting coronal mass ejections (CMEs). Notably, this AR exhibits exceptionally rapid magnetic flux emergence. The eruptions on which we focus all occurred along collisional polarity inversion lines (PILs) through collisional shearing during a three-day period of extraordinarily high flux emergence (sim 1021 Mx hr$^ $). Our key findings reveal how photospheric magnetic configurations in eruption sources influence solar superstorm formation and geomagnetic responses, and link exceptionally strong flux emergence to sequential homologous eruptions: (1) We identified the source regions of seven halo CMEs that were distributed primarily along two distinct PILs. This distribution suggests two groups of homologous CMEs. (2) The variations in the magnetic flux emergence rates in the source regions are correlated with the CME intensities. This might explain the two contrasting cases of complex ejecta that are observed at Earth. (3) Our calculations of the magnetic field gradients around the CME source regions show strong correlations with eruptions. This provides crucial insights into solar eruption mechanisms and enhances our prediction capabilities for future events.

Magnetic field sensor based on multiple Fano resonance in metal-insulator-metal waveguide coupled with cross-shape resonator

Abstract In this paper, an innovative plasmonic magnetic field sensor (MFS) that exploits a Metal-insulator-Metal (MIM) waveguide configuration with an asymmetric cross-shaped resonator is constructed. The design enables the observation of double Fano resonance in the transmission spectrum, resulting from the coupling between continuous spectrum and discrete spectrum. By incorporating magnetic fluid in the asymmetric cross-shape resonator, the Fano line shapes can be tuned by the external magnetic field. Finite-Difference Time-Domain (FDTD) is used to simulate the spectra response to external magnetic fields and geometrical sizes. The proposed structure exhibits remarkable magnetic field sensitivity of 12.1 p m / O e within the detection range of 15 O e to 199 O e . The resolution of MIM magnetic field sensors can reach 0.0826 O e . The optimal figure of merit (FOM) and maximum Q factor of the Fano dip are about 6.9 × 10 − 4 / O e and 66.74, respectively. Meanwhile, The proposed Fano resonance MFS has some advantages, including compact size, high sensitivity, and cost-effectiveness. A strong linear relationship between the magnetic field and resonance wavelength indicates that the proposed structure can find potential applications in diverse fields such as magnetic field sensors, aircraft navigation, and even nuclear energy generation.

Magnetoelectric Coupling in a Mn4Na-Organic Complex under Pulsed Magnetic Fields up to 73 T.

Research on the magnetoelectric (ME) effect (or spin-electric coupling) in molecule-based magnetic materials is a relatively nascent but promising topic. Molecule-based magnetic materials have diverse magnetic functionalities that can be coupled to electrical properties. Here we investigate a realization of ME coupling that is fundamental but not heavily studied─the coupling of magnetic spin level crossings to changes in electric polarization. A mixed-valence Mn4Na complex with a total ground-state spin S = 5/2 under zero magnetic field and S = 17/2 under high magnetic field undergoes a cascade of ground-state level crossings of the Sz states with increasing magnetic field. Magnetization and electrical polarization measurements under pulsed magnetic fields up to 73 T show that each spin level crossing is accompanied by a significant change in electric polarization that is an even function of the applied magnetic field. A molecular Hamiltonian describing antiferromagnetic exchange in a distorted tetrahedron of three MnIII and one MnII ions matches the data well. We conclude that the ME coupling is caused by magnetostriction within the polar molecule as it distorts to lower its magnetic exchange energy.

Large photoresistance and photoinduced magnetoresistance in La0.67Ca0.33MnO3 thin film on silicon substrate

Abstract The effects of light illumination and magnetic field on the electrical transport properties of La0.67Ca0.33MnO3 thin film on a silicon substrate have been studied in detail. Large value of colossal magnetoresistance has been observed under an applied magnetic field in the whole temperature range below 150 K which is related to the presence of both antiferromagnetic and ferromagnetic phase in the sample. A significant amount of resistance drop is caused by light illumination even at extremely low light intensities, ∼−22% with light of 0.3 μW cm−2 intensity and ∼−42% with 6.2 μW cm−2 intensity at 600 nm wavelength. There has been a notable rise in the photoinduced magnetoresistance value, specifically, a significant decrease in resistance occurs in simultaneous presence of magnetic field and light. For 1 T applied magnetic field, MR% rises from −33% in dark to −58% under light illumination at 150 K i.e. ΔMR% is 25%. As the strength of the magnetic field increases, ΔMR% decreases, suggesting that the magnetoresistive photoinduced phenomenon is more pronounced in the presence of mix phases in the sample. This combined enhanced magnetoresistive photoinduced phenomenon is explained by the interaction of photogenerated charge carriers in the sample and applied magnetic field.