Behavior Of Magnetic Field Research Articles

Single-site magnetic anisotropy governed by interlayer cation charge imbalance in triangular-lattice AYbX2

The behavior in magnetic field of a paramagnetic center is characterized by its $g$ tensor. An anisotropic form of the latter implies different kind of response along different crystallographic directions. Here we shed light on the anisotropy of the $g$ tensor of Yb$^{3+}$ 4$f^{13}$ ions in NaYbS$_2$ and NaYbO$_2$, layered triangular-lattice materials suggested to host spin-liquid ground states. Using quantum chemical calculations we show that, even if the ligand-cage trigonal distortions are significant in these compounds, the crucial role in realizing strongly anisotropic, `noncubic' $g$ factors is played by inter-layer cation charge imbalance effects. The latter refer to the asymmetry experienced by a given Yb center due to having higher ionic charges at adjacent metal sites within the magnetic $ab$ layer, i.e., 3+ nearest neighbors within the ab plane versus 1+ species between the magnetic layers. According to our results, this should be a rather general feature of 4$f^{13}$ layered compounds: less inter-layer positive charge is associated with stronger in-plane magnetic response.

Weak palaeointensity results over a Pliocene volcanic sequence from Lesser Caucasus (Georgia): transitional record or time averaged field?

SUMMARY A palaeointensity study has been carried out on a Pliocene sequence of 20 consecutive lava flows where previous directional results seem to reflect anomalous behaviour of the Earth's magnetic field (EMF), which can be explained by a polarity transition record or non-averaged palaeosecular variation or both. Here, we perform a total of 55 palaeointensity determinations using the original Thellier–Thellier (TT) method and 100 with the IZZI method. We assess the performance of our selection criteria using a set of strict threshold values applied to a set of test data whose TRMs were acquired in known fields. Absolute palaeointensity determinations that passed our selection criteria were obtained on four specimens with the TT method and on 41 specimens with the IZZI method. Application of reliability criteria at a site level yielded palaeointensity results in 8 of 20 studied lava flows. We obtained median values of VADM between 28.9 and 45.6 ZAm2 for the reverse polarity lower Apnia section, while the normal polarity upper section displayed a single value of 54.6 ZAm2. The low palaeointensity values before a transitional direction lava flow and the higher value after it, suggest the common behaviour at the start of a polarity reversal and the recovery after it. However, an isolated record of a stable EMF, where the intensity is lower than the current for the same location (83.7 ZAm2), cannot be discarded. Consequently, this interpretation would support a weak time-averaged field.

Behavior of nanocomposite consisting of manganese ferrite particles and atomic layer deposited bismuth oxide chloride film

Nanocomposites of manganese ferrite and bismuth oxide chloride were synthesized. The composites consisted of 10 nm thick nanocrystalline bismuth oxide chloride thin film grown by atomic layer deposition on spinel MnFe2O4 nanoparticles prepared by wet chemical synthesis. The composite layers exhibited nonlinear polarization behavior in both magnetic and electric fields at room temperature. The magnetic coercive force, HC, was 30–40 Oe at room temperature. The width of electrical charge – voltage hysteresis loop reached 3.6 MV/cm.

Generalized Tikhonov's algorithm for accurate calculation of one‐dimensional transient responses directly in time domain

ABSTRACTIn the last two decades, forward modelling for the time domain (transient) electromagnetic method has concentrated almost entirely on multi‐dimensional models and algorithms. At the same time, the interpretation of real field data is still mainly one dimensional. This is caused by the lack of an efficient multi‐dimensional acquisition procedure supported by sufficiently fast and reliable inversion software, on the one hand, and by the great efficiency of one‐dimensional field set up and interpretation of the data on the other hand. The latter is particularly true for the short offset transient electromagnetic method, which is much less sensitive to multi‐dimensional effects, compared to long offset methods. The most commonly used one‐dimensional forward modelling algorithms are based on the spectral method, which requires calculating rapidly oscillating Fourier–Bessel (Hankel) integrals. Due to the very fast decay of short offset responses, the integrals become computationally unstable at late times of the transient process. Although this problem has been successfully solved for practically feasible measurement times of conventional short offset systems using transverse electric and mixed transverse electric and transverse magnetic fields, it turned out crucial for novel methods based on the use of unimodal transverse magnetic fields. These methods are much more sensitive to geoelectric parameters of the Earth in general and those of resistive targets, in particular, but they generate responses, which drop at late times significantly faster than those of conventional methods. Such behaviour of transverse magnetic fields represents severe computational problem for the spectral method, but is successfully solved by direct time domain algorithms. This article describes a generalization of the well‐known Tikhonov's solution to a boundary value problem directly in time domain, which is applied to an arbitrary one‐dimensional earth model excited by an arbitrary source. Contrary to existing spectral algorithms, the described method allows accurate calculations of both transverse electric and transverse magnetic transient responses at arbitrarily late times. On the other hand, it is more time efficient than finite‐difference/finite element direct time domain algorithms and provides analytical late‐stage asymptotic solutions.

Synergistic Inhibition Effect of Magnetic Field and Inhibitors against Carbon Steel Corrosion in CO2-Saturated Oilfield-Produced Water

In this work, the synergistic inhibition behavior and mechanism of magnetic field (MF) and inhibitors against carbon steel corrosion in CO2-saturated oilfield-produced water were investigated using...

An assessment of long duration geodynamo simulations using new paleomagnetic modeling criteria (QPM)

Long-term temporal variations of the magnetic field (timescales >10 Myr), characterized from paleomagnetic data, have been hypothesized to reflect the evolution of Earth's deep interior and couplings between the core and mantle. By tying observed changes in the paleomagnetic record to mechanisms predicted from numerical geodynamo simulations, we have a unique tool for assessing changes in the deep interior back in time. However, numerical simulations are not run in an Earth-like parameter regime and assessing how well they reproduce the geomagnetic field is difficult. Criteria have been proposed to determine the level of spatial and temporal agreement between simulations and observations spanning historical and Holocene timescales, but no such criteria exist for longer timescales. Here we present a new set of five criteria (Quality of Paleomagnetic Modeling criteria, QPM) that assess the degree of semblance between a simulated dynamo and the temporal and spatial variations of the long-term (∼10 Myr) paleomagnetic field. These criteria measure inclination anomaly, virtual geomagnetic pole dispersion at the equator, latitudinal variation in virtual geomagnetic pole dispersion, normalized width of virtual dipole moment distribution, and dipole field reversals. We have assessed 46 geodynamo simulations using the QPM criteria. The simulations have each been run for the equivalent of at least ∼300 kyr, span reversing and non-reversing regimes, and include either homogeneous or heterogeneous heat flux boundary conditions. We find that none of our simulations reproduce all salient aspects of the long-term paleomagnetic field behavior for the past 10 Myr. Nevertheless, our simulations bracket Earth values, suggesting that an Earth-like simulation is feasible within the available computationally accessible parameter space. This new set of criteria can inform future simulations that aim to reproduce all aspects of Earth's long-term magnetic field behavior.

Synchronizing volcanic, sedimentary, and ice core records of Earth's last magnetic polarity reversal.

Reversal of Earth's magnetic field polarity every 105 to 106 years is among the most far-reaching, yet enigmatic, geophysical phenomena. The short duration of reversals make precise temporal records of past magnetic field behavior paramount to understanding the processes that produce them. We correlate new 40Ar/39Ar dates from transitionally magnetized lava flows to astronomically dated sediment and ice records to map the evolution of Earth's last reversal. The final 180° polarity reversal at ~773 ka culminates a complex process beginning at ~795 ka with weakening of the field, succeeded by increased field intensity manifested in sediments and ice, and then by an excursion and weakening of intensity at ~784 ka that heralds a >10 ka period wherein sediments record highly variable directions. The 22 ka evolution of this reversal suggested by our findings is mirrored by a numerical geodynamo simulation that may capture much of the naturally observed reversal process.

Vacuum Arc Cathode Spot Theory: History and Evolution of the Mechanisms

Vacuum arc cathode spot theories are reviewed, beginning from the primary studies in second half of the 19th century up to the present. The evolution of the main ideas is presented, starting from those, which developed, for separate phenomena, up to systematic inclusive models. New spot type classifications are proposed based on observed characteristics, instead of the previous simple numbering. Different approaches were considered for generating plasma comprised of cathode material, based on cathode vaporization and local explosions. Models with closed systems of equations were developed. A kinetic model advantageously allows calculating the cathode potential drop. These closed models explain various phenomena and two base rules were derived: 1) impeded plasma flow enables cathode spot operation and 2) the heat loss in the cathode must be smaller than the energy input to the cathode spot. Based on these rules, mechanisms for the spot types were derived and observed spot behavior in transverse and oblique magnetic fields was described.

Evaluation of Electromagnetic Behavior of No-Insulation REBCO Pancake Coil With Multiple Defects

We previously developed a high-magnetic-field REBCO coil for use in medical devices such as medical accelerators and high-magnetic-field MRI. The use of high-temperature superconducting (HTS) coils in such applications necessitates their miniaturization while providing high magnetic fields. However, when the current density is improved by reducing the copper-stabilization-layer thickness in the conventional insulated HTS coil, the thermal stability is lowered, which leads to a tradeoff between high current density and high thermal stability. Therefore, we examine no-insulation (NI) coils that allow compatibility between high current density and thermal stability. Recent research has indicated that NI coils with multiple defects can afford a stable and high critical current (Ic) and operate without serious problems, which makes it possible to produce coils wound with commercial REBCO tapes containing several defects along the tape, which in turn makes fabrication economically viable. However, there are many unknown aspects of the current, magnetic field, and heat behaviors of NI coils with defects, particularly when large currents flow through them. Here, in order to examine the behavior of a multiple-defect NI coil subjected to a large current at the temperature of ~30 K via application of the conduction cooling method, we use a combination of the partial element equivalent circuit method and the finite-element method to investigate the detailed current and thermal behaviors. Our results indicate that defective NI coils can afford a critical current Ic value of ~80% of that of defect-free NI coils, which makes our findings valuable in terms of contributing to further developments in HTS coil applications.

Spontaneous spin-nematic ordering in a spin-chain system

The spontaneous onset of the spin-nematic order in spin-chain systems is studied. The ordering persists due to distortions of either magnetic ions, or ligands taking part in the superexchange between magnetic ions. The spin-nematic order yields a nonzero biaxial magnetic anisotropy for the spin chain, violating the U(1) symmetry. The influence of the external magnetic field and nonzero temperature is considered. We predict how the spin-nematic ordering can manifest itself in the temperature and magnetic field behavior of magnetoacoustic characteristics.

Tailoring the ferrimagnetic-to-ferromagnetic transition field by interstitial and substitutional atoms in the R–Fe compounds

Fundamental characteristics of rare-earth (R) – iron intermetallics R2Fe14B are highly sensitive to the atomic substitutions and interstitial absorption of light elements. We studied a combined influence of the substitutions in the rare-earth sublattice and hydrogen absorption on the magnetization behavior in magnetic fields up to 60 T Er2Fe14B and Tm2Fe14B ferrimagnets chosen for the study showed that the substitution of Nd for Er or Tm increases the saturation magnetization as a result of ferromagnetic ordering of Nd and Fe moments. Under sufficiently high magnetic fields the magnetic moments rotate and the field-induced ferromagnetic state may be observed. The field at which a transition occurs is related to the strength of the inter-sublattice exchange interaction. The role of hydrogen is primarily to weaken the inter-sublattice ferrimagnetic coupling so that the reorientation becomes achievable at the available magnetic field strength (in hydrides Tm2Fe14BH5.5 and (Tm0.5Nd0.5)2Fe14BH5.5). We analyze the volume dependence of the R–Fe magnetic interaction in R2Fe14B and compare it with other R–Fe compounds.

Combining the Magnetic Equivalent Circuit and Maxwell–Fourier Method for Eddy-Current Loss Calculation

In this paper, a hybrid model in Cartesian coordinates combining a two-dimensional (2-D) generic magnetic equivalent circuit (MEC) with a 2-D analytical model based on the Maxwell–Fourier method (i.e., the formal resolution of Maxwell’s equations by using the separation of variables method and the Fourier’s series) is developed. This model coupling has been applied to a U-cored static electromagnetic device. The main objective is to compute the magnetic field behavior in massive conductive parts (e.g., aluminum, magnets, copper, iron) considering the skin effect (i.e., with the eddy-current reaction field) and to predict the eddy-current losses. The magnetic field distribution for various models is validated with 2-D and three-dimensional (3-D) finite-element analysis (FEA). The study is also focused on the discretization influence of 2-D generic MEC on the eddy-current loss calculation in conductive regions. Experimental tests and 3-D FEA have been compared with the proposed approach on massive conductive parts in aluminum. For an operating point, the computation time is divided by ~4.6 with respect to 3-D FEA.

All-Loop Result for the Strong Magnetic Field Limit of the Heisenberg-Euler Effective Lagrangian.

We provide an explicit expression for the strong magnetic field limit of the Heisenberg-Euler effective Lagrangian for both scalar and spinor quantum electrodynamics. To this end, we show that the strong magnetic field behavior is fully determined by one-particle reducible contributions discovered only recently. The latter can efficiently be constructed in an essentially algebraic procedure from lower-order one-particle reducible diagrams. Remarkably, the leading strong magnetic field behavior of the all-loop Heisenberg-Euler effective Lagrangian only requires input from the one-loop Lagrangian. Our result revises previous findings based exclusively on one-particle irreducible contributions. In addition, we briefly discuss the strong electric field limit and comment on external field QED in the large N limit.

Magnetic Field during Wireless Charging in an Electric Vehicle According to Standard SAE J2954

The Society of Automotive Engineers (SAE) Recommended Practice (RP) J2954 (November 2017) was recently published to standardize the wireless power transfer (WPT) technology to recharge the battery of an electric vehicle (EV). The SAE J2954 RP establishes criteria for interoperability, electromagnetic compatibility (EMC), electromagnetic field (EMF) safety, etc. The aim of this study was to predict the magnetic field behavior inside and outside an EV during wireless charging using the design criteria of SAE RP J2954. Analyzing the worst case configurations of WPT coils and EV bodyshell by a sophisticated software tool based on the finite element method (FEM) that takes into account the field reflection and refraction of the metal EV bodyshell, it is possible to numerically assess the magnetic field levels in the environment. The investigation was performed considering the worst case configuration—a small city car with a Class 2 WPT system of 7.7 kVA with WPT coils with maximum admissible ground clearance and offset. The results showed that the reference level (RL) of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines in terms of magnetic flux density was exceeded under and beside the EV. To mitigate the magnetic field, the currents flowing through the WPT coils were varied using the inductor-capacitor-capacitor (LCC) compensation instead of the traditional series-series (SS) compensation. The corresponding calculated field was compliant with the 2010 ICNIRP RL and presented a limited exceedance of the 1998 ICNIRP RL. Finally, the influence of the body width on the magnetic field behavior adopting maximum offset was investigated, demonstrating that the magnetic field emission in the environment increased as the ground clearance increased and as the body width decreased.

High-temperature soft magnetic behavior of magnetic field annealed Finemet-type nanocrystalline alloys

The soft magnetic behaviors at elevated temperatures for magnetic field annealed nanocrystalline Fe73.5Cu1Nb3Si13.5B9, (Fe0.5Co0.5)73.5Cu1Nb3Si13.5B9 and Ni10(Fe0.5Co0.5)63.5Cu1Nb3Si13.5B9 alloys were investigated by the temperature evolution of initial permeability (μi-T curve). The results show that magnetic field annealing gives rise to a persistent increasing μi from room temperature to a relatively higher temperature for Co- and NiCo-containing Finemet. Especially for the magnetic field annealed NiCo-containing Finemet, the μi is evidently improved in the temperature range between 200-600°C with respect to the sample without magnetic field annealing.

New Design and Magnetic Field Analysis of Transformer Shape with V-Connection for Core Loss Reduction in Railway System

This paper presents a new design of transformer shape core used in railway system for loss reduction analyzed via the magnetic vector potential in the form of partial differential equation related to magnetic field. Finite element method is used in order to simulate a three-dimensional system. This paper focuses on the core loss reduction which is calculated from magnetic vector potential and magnetic field behavior on core transformer with V-connection, while the transformer has supplied voltage from three-phase system. The unbalanced input voltage is divided into three case studies in this paper: C-A couple phase, A-B couple phase and B-C couple phase from three-phase system. In addition, a design of transformer shape core has occurred on the corner that is the intersection between vertical core and horizontal core with 5 mm radius curves. The simulation results compare core loss of transformer between the original shape of transformer core and the new design of transformer core even though the supplied voltage is unbalanced. However, the results have shown that the new design of transformer core can decrease the core loss and it can lead to develop the shape of transformer core in order to reduce the core loss in term of manufacturing.

Magnetic-Field-Induced Suppression of Jahn-Teller Phonon Bands in (La0.6Pr0.4)0.7Ca0.3MnO3: the Mechanism of Colossal Magnetoresistance shown by Raman Spectroscopy

A long-standing issue in the physics of the colossal magnetoresistance is the role of electron-phonon coupling, which manifests itself as Jahn-Teller polarons. The origin and architecture of polarons makes it possible to study their behavior by Raman spectroscopy, which allows to analyze the polaronic behavior in an applied magnetic field. We performed magnetic-field-dependent Raman spectroscopy on thin films of (La0.6Pr0.4)0.7Ca0.3MnO3 in a range of H = 0–50 kOe and compared the obtained Raman spectra with the magnetic field behavior of the electrical resistivity. In the vicinity of the Curie temperature, TC = 197 K, the intensity of the Jahn-Teller stretching mode at 614 cm−1 and of the bending mode at 443 cm−1 was found to be suppressed and enhanced, respectively. This observed behavior has a remarkable similarity with the field and temperature dependence of the colossal magnetoresistance in (La0.6Pr0.4)0.7Ca0.3MnO3. Our work provides direct evidence that the reduction of the amount of Jahn-Teller polarons at the phase transition is the main mechanism underlying the colossal magnetoresistance.

Divalent Thulium Crown Ether Complexes with Field-Induced Slow Magnetic Relaxation.

The tailoring of the coordination chemistry around f-element centers is a crucial step for the development of compounds with slow magnetic relaxation, including single-molecule magnets (SMMs), which have great potential in molecular spintronics and for future quantum computing devices. Lanthanide ions are particularly interesting because the predominant electrostatic model of their bonding allows rationalizing their coordination symmetry. However, to the best of our knowledge, the redox properties of the lanthanides are not taken into account for the design of SMMs, and therefore all SMMs reported to date contain lanthanide ions in their trivalent oxidation state. In this Article, divalent lanthanide compounds presenting field-induced slow magnetic relaxation are reported. The rational design and synthesis of two TmII complexes with the 18-crown-6 ligand are presented along with their emission and EPR properties, which help to probe the desired nature of the ground state, that is, maximizing the anisotropy. The observed magnetic properties demonstrate their slow magnetic relaxation behavior in a moderate external magnetic field.

Negative longitudinal magnetoresistance in gallium arsenide quantum wells

Negative longitudinal magnetoresistances (NLMRs) have been recently observed in a variety of topological materials and often considered to be associated with Weyl fermions that have a defined chirality. Here we report NLMRs in non-Weyl GaAs quantum wells. In the absence of a magnetic field the quantum wells show a transition from semiconducting-like to metallic behaviour with decreasing temperature. We observe pronounced NLMRs up to 9 Tesla at temperatures above the transition and weak NLMRs in low magnetic fields at temperatures close to the transition and below 5 K. The observed NLMRs show various types of magnetic field behaviour resembling those reported in topological materials. We attribute them to microscopic disorder and use a phenomenological three-resistor model to account for their various features. Our results showcase a contribution of microscopic disorder in the occurrence of unusual phenomena. They may stimulate further work on tuning electronic properties via disorder/defect nano-engineering.

Longitudinal magnetization and specific heat of the anisotropic heisenberg antiferromagnet on honeycomb lattice

We study the effects of longitudinal magnetic field and temperature on the thermodynamic properties of two dimensional Heisenberg antiferromagnet on the honeycomb lattice in the presence of anisotropic Dzyaloshinskii-Moriya interaction and next nearest neighbor coupling exchange constant. In particular, the temperature dependence of specific heat have been investigated for various physical parameters in the model Hamiltonian. Using a hard core bosonic representation, the behavior of thermodynamic properties has been studied by means of excitation spectrum of mapped bosonic gas. The effect of Dzyaloshinskii-Moriya interaction term on thermodynamic properties has also been studied via the bosonic model by Green's function approach. Furthermore we have studied the magnetic field dependence of specific heat and magnetization for various anisotropy parameters. At low temperatures, the specific heat is found to be monotonically increasing with temperature for magnetic fields in the gapped field induced phase region. We have found the magnetic field dependence of specific heat shows a monotonic decreasing behavior for various magnetic fields due to increase of energy gap in the excitation spectrum. Also we have studied the dependence of magnetization on Dzyaloshinskii-Moriya interaction strength for different next nearest neighbor coupling constant.