External Static Field Research Articles

To age or not to age: Anatomy of a supercooled liquid's response to a high alternating electric field.

Physical aging and structural recovery are the processes with which the structure of a system approaches equilibrium after some perturbation. Various methods exist, that initiate structural recovery, such as changing the temperature or applying a strong, external static field. This work is concerned with high alternating electric fields and their suitability to study structural recovery and aging. The present work demonstrates that rationalizing the nonlinear dielectric response of a supercooled liquid to high-amplitude ac-fields requires multiple fictive temperatures. This feature is in stark contrast to structural recovery after a temperature down-jump or a considerable increase in the static electric field, for which a single parameter, the fictive temperature or material time, describes the structural change. In other words, the structural recovery from a high ac-field does not adhere to time aging-time superposition, which is so characteristic of genuine aging processes.

Precession Dynamics of the Uniaxial Nanoparticle Magnetization in the Ferromagnetic Resonance Region

The influence of the shape parameter (oblateness) of a uniaxial ellipsoidal nanoparticle on the dynamics of its magnetic moment upon magnetization along the symmetry axis and excitation by a weak transverse high-frequency field in the region of parameters where the equilibrium magnetic moment of the nanoparticle and the external static field is noncollinear has been studied. It is shown that as the oblateness increases, the irregularity of the oscillations increases, which at first affects only their amplitude, but then also the time dependence. The intervals of the shape parameter (or frequency), where various nonlinear modes of precession are realized --- dynamic bistability, complex spatial attractors and chaos, were revealed using bifurcation diagrams. Keywords: ellipsoidal nanoparticle, "easy" axis, effective anisotropy, ferromagnetic resonance, high frequency field, bistability, regular and chaotic precession.

Прецессионная динамика намагниченности одноосной наночастицы в области ферромагнитного резонанса

The influence of the shape parameter (oblateness) of a uniaxial ellipsoidal nanoparticle on the dynamics of its magnetic moment upon magnetization along the symmetry axis and excitation by a weak transverse high-frequency field in the region of parameters where the equilibrium magnetic moment of the nanoparticle and the external static field is noncollinear has been studied. It is shown that as the oblateness increases, the irregularity of the oscillations increases, which at first affects only their amplitude, but then also the time dependence. The intervals of the shape parameter (or frequency), where various nonlinear modes of precession are realized - dynamic bistability, complex spatial attractors and chaos, were revealed using bifurcation diagrams.

Slow Magnetic Relaxation in Cobalt(II) Complexes with One-Dimensional Hydrogen-Bonded Networks

Two new cobalt(II) complexes with an unsymmetrical bidentate ligand, 2-(1,4,5,6-tetrahydropyrimidin-2-yl)-6-methoxyphenol (H2mthp), were synthesized and crystallographically characterized. Tetra- and hexa-coordinate mononuclear complexes were selectively obtained by adjusting the stoichiometry of the base. The coordination geometry of hexa-coordinated complex was severely distorted from an ideal octahedron, due to the NO5 coordination environment from the mixed coordination of one Hmthp− and two H2mthp ligands. Both complexes formed one-dimensional chain networks by hydrogen-bond and N-H···π interactions. Single-molecule magnet behavior was observed for the tetrahedral complex under zero magnetic field. The relatively short Co···Co distances induced non-zero intermolecular magnetic coupling, which split the ground ±Ms levels to suppress quantum-tunneling of magnetization. In the octahedral complex, by contrast, the distance was not short enough to induce the coupling. As a consequence, single-molecule magnetic behavior was observed for the octahedral complex only in the presence of an external static field.

Metastability for the degenerate Potts model with negative external magnetic field under Glauber dynamics

We consider the ferromagnetic q-state Potts model on a finite grid with a non-zero external field and periodic boundary conditions. The system evolves according to Glauber-type dynamics described by the Metropolis algorithm, and we focus on the low temperature asymptotic regime. We analyze the case of a negative external magnetic field. In this scenario, there are q − 1 stable configurations and a unique metastable state. We describe the asymptotic behavior of the first hitting time from the metastable state to the set of the stable states as β → ∞ in probability, in expectation, and in distribution. We also identify the exponent of the mixing time and find an upper bound and a lower bound for the spectral gap. We identify the minimal gates for the transition from the metastable state to the set of the stable states and for the transition from the metastable state to a fixed stable state. Furthermore, we identify the tube of typical trajectories for these two transitions. The detailed description of the energy landscape that we develop allows us to give precise asymptotics for the expected transition time from the unique metastable state to the set of the stable configurations.

Indefinite causal order with fixed temporal order for electrons and positrons

We provide an analysis of indefinite causal orders in relativistic quantum mechanics based on the electron–positron picture of Feynman involving negative energy electrons ‘moving backward in time’ (i.e., involving a retrocausal link). We show that genuine implementations of the paradigmatic quantum switch, but here violating some causal inequalities and with a fixed temporal order, become possible in extreme external electromagnetic field conditions.

Comparison of the Effects of Ultrasonic and Ball Milling on Red Mud Desulfurization

Red mud desulfurization is an environmentally friendly desulfurization technology. After desulfurization, the acidity of red mud slurry continues to be neutralized for processing new red mud, and no waste acid is generated. At present, there is a lack of research on desulfurization intensification in external fields, etc. To further enhance red mud desulfurization, this paper used an SO2 detector, X-ray fluorescence spectrometer (XRF), and scanning electron microscope (SEM) to compare and analyze red mud desulfurization under the action of ball mill and ultrasonic external fields. In this study, experiments were conducted using a bubbling and stirring reactor device. The results showed that the suitable red mud slurry concentration was 10 g/L. The raw red mud desulfurization (without external field condition) could reach 100% absorption in the first 25 min, and the desulfurization rate dropped to 81.3% at 80 min. The mechanism of red mud desulfurization was investigated by X-ray diffractometer (XRD), XRF, and infrared spectroscopy. Under the action of the external field of the ball mill, the red mud particles could be refined to prolong the desulfurization time. The red mud after ball milling could reach 100% absorption within 33 min. Under the thermal effect of the ultrasound, 100% absorption could only be achieved within 23 min. From the desulfurization effect and XRF results, it was found that the ball mill was more suitable for promoting red mud desulfurization in the bubbling and stirring reactor.

Surface Resistance and Amplitude Mode under Uniform and Static External Field in Conventional Superconductors

We calculate the surface resistance of s-wave superconductors under a static external field on the basis of the quasiclassical approximation. The numerical calculations are performed both for the dirty and relatively clean cases, and the difference in the absorption spectrum between them is investigated. The amplitude mode in the dirty case, which has been previously studied in the local response function, appears also in the nonlocal response. In the clean case, there is a large discrepancy between the excitation energy of the amplitude mode and the energy of the gap edge where the coupling between the electrons and the external field is effective. Therefore, the amplitude mode exists even when the superconductor is relatively clean, but its contribution to the response function is small. These behaviors, which are qualitatively consistent with the experimental results, are obtained by taking into account the static field nonperturbatively.

Mirau interferometry of fluid interfaces deformed by colloids under the influence of external fields

The interfacial curvature surrounding colloidal particles pinned to fluid interfaces dictates their interparticle capillary interaction and assembly; however, it is a nontrivial function of particle anisotropy, surface roughness, external field conditions, macroscopic interfacial curvature, and the chemistry of each fluid phase. The prospect of dynamically modifying the pinning properties and interfacial organization of colloidal particles adhered to fluid interfaces via these approaches necessitates the development of experimental techniques capable of measuring changes in the interfacial deformation around particles in situ. Here, we describe a modified technique based on phase-shift Mirau interferometry to determine the relative height of the fluid interface surrounding adsorbed colloids while applying external electric fields. The technique is corrected for macroscopic curvature in the interface as well as in-plane motion of the particle in order to isolate the contribution of the particle to the interfacial deformation. Resultant height maps are produced with a maximum resolution of ±1nm along the height axis. The measured topography of the interface is used to identify the contact line where the two fluids meet the particle, along with the maximal interfacial deformation (Δumax) of the undulating contact line and the three-phase contact angle, θc. The technique is calibrated using anisotropic polymer ellipsoids of varying aspect ratio before the effect of external AC electric fields on the pinned particle contact angle is demonstrated. The results show promise for this new technique to measure and quantify dynamic changes in interfacial height deformation, which dictate interparticle capillary energy and assembly of colloids at fluid interfaces.

Particle-in-cell model of a relativistic magnetron system driven by a pulse forming network Marx generator

A three dimensional particle-in-cell (PIC) model of a relativistic magnetron (RM) is established using CST Studio Suite. As we adopted a novel technique to imitate pulse forming action of pulser, simulation domain is now fully extended to include a pulser, a transmission line, and a magnetron tube. This feature enables the model to describe a dynamic power coupling process between the pulser and RM in a self-consistent manner. It is demonstrated that model accuracy is strongly dependent on user-defined parameters for an explosive electron emission model. Particularly, emission rise time for space charge formation influences significantly on an initial mode competition phase. Compared to a previous excitation method using a step voltage pulse, the new model gives more reliable results as the intrinsic impedance of the pulser is now considered. Our model is able to estimate the major RM characteristics over a wide range of an external magnetic field. As a result of dynamic power coupling, the RM impedance, the gap voltage, the excitation frequency, and the output power tend to increase at a higher external magnetic field condition. It is suitable to adopt a proposed modeling technique for the virtual assemble and simulation of the system. Hence, it will suggest a practical way to implement and verify complicated structures or innovative designs that could not be solved by existing PIC codes.

Dynamics of magnetization of a uniaxial nanoparticle in the region of noncollinear ferromagnetic resonance

Resonance dynamics of the magnetic moment of a uniaxial ellipsoidal nanoparticle under its magnetic biasing along the symmetry axis and excitation by a transverse high-frequency field is studied with the parameters (frequency, magnetic bias field and shape parameter), corresponding to the noncollinear orientation of equilibrium magnetization and the external static field. We revealed the frequency regions where precession becomes nonlinear at a weak alternating field and dynamic bistability, as well as complex spatial attractors and chaos are implemented. Keywords: ellipsoidal nanoparticle, ferromagnetic resonance, static and high-frequency field, nonlinearity, effective anisotropy, bistability, regular and chaotic precession.

Numerical simulation of contact and separation of magnetic particles under uniform magnetic field

Under the action of an external magnetic field, the magnetic particles will be arranged along the direction of the magnetic field. The laws of physics that control these processes are well described in the literature. However, when the magnetic particles move in the fluid, the magnetic particles with different initial distances have different mutual influences, so there will be different laws of motion. Therefore, based on the motion theory of magnetic particles in Stokes fluid, this article discusses the motion law of the contact and separation of two circular magnetic particles in Newtonian fluid. First, we conduct theoretical and simulation modeling of two magnetic particles under the action of a uniform magnetic field, and verify the correctness of the simulation through experiments; secondly, we use numerical simulation to study the angle of repulsion and attraction of magnetic particles at different initial distances, and analyze at the same time the changes in the trajectory, speed, torque and force of magnetic particles in the process of motion are studied. Finally, the influence of external field conditions on the phenomenon of contact and separation of magnetic particles is studied. The study found that even when the initial angle between the magnetic particles is 90° with the direction of the magnetic field, the magnetic particles with different initial distances will repel under the action of repulsive force and then contact again and keep repelling these two states, a better explanation the reason for the agglomeration of magnetic particles at close range is explained.

Magnetic field-induced alignment of nickel-coated copper nanowires in epoxy composites for highly thermal conductivity with low filler loading

In this work, the large-scale produced copper nanowires (Cu NWs) were coated by nickel nanoparticles (Ni NPs) lay, i.e., Cu NWs@Ni. And under external magnetic field condition, Cu NWs@Ni as thermally conductive fillers were filled into epoxy (EP) resin to prepare the composites with high thermal conductivity (TC). The results showed that, when the magnetic field was 80 mT, Cu NWs@Ni (molar ratio of Cu:Ni = 10:5, and saturation magnetization (Ms) = 20.3 emu/g) can distribute in EP resin in an orderly manner along the direction of the magnetic field, endowing the composite with excellent TC at lower loading. Especially, when only 9 vol% Cu NWs@Ni was filled, the TC along the direction of the magnetic field can reach 2.90 W/mK, which was 12.81 times than that of neat EP resin. Even so, the composite still maintained outstanding insulation properties, namely, the volume resistivity and the dielectric strength were 1.79 × 1015 Ω cm and 12.88 kV/mm, respectively. In addition, compared to that of neat EP resin, the composite still possessed splendid heat stability and mechanical properties. For the above positive improvement, the corresponding mechanisms were also discussed in detail.

Spin-Phonon Coupling and Slow-Magnetic Relaxation in Pristine Ferrocenium.

We report the spin dynamic properties of non‐substituted ferrocenium complexes. Ferrocenium shows a field‐induced single‐molecule magnet behaviour in DMF solution while cobaltocene lacks slow spin relaxation neither in powder nor in solution. Multireference quantum mechanical calculations give a non‐Aufbau orbital occupation for ferrocenium with small first excitation energy that agrees with the relatively large measured magnetic anisotropy for a transition metal S=1/2 system. The analysis of the spin relaxation shows an important participation of quantum tunnelling, Raman, direct and local‐mode mechanisms which depend on temperature and the external field conditions. The calculation of spin‐phonon coupling constants for the vibrational modes shows that the first vibrational mode, despite having a low spin‐phonon constant, is the most efficient process for the spin relaxation at low temperatures. In such conditions, vibrational modes with higher spin‐phonon coupling constants are not populated. Additionally, the vibrational energy of this first mode is in excellent agreement with the experimental fitted value obtained from the local‐mode mechanism.

Electromagnetic resonance of nonlinear vacuum in one-dimensional cavity

Nonlinear corrections on electromagnetic fields in vacuum have been expected. In this study, we have theoretically considered nonlinear Maxwell’s equations in a one-dimensional cavity for a classical light and external static electromagnetic fields. A general solution for the electromagnetic corrective components including that of a longitudinal standing wave was derived after a linearization. The main purpose is to give a detailed feature of the previously reported resonant behavior [Shibata, Euro. Phys. J. D 74:215 (2020)], such as the effect of external static fields and the polarization fluctuation. These results favor the development of new and effective method for experiment.Graphic abstract

Nonstationary equation for the one-particle wave function of the Bose–Einstein condensate

Based on the self-consistent Hartree–Fock approximation, the nonstationary equation is obtained for the one-particle wave function describing the Bose–Einstein condensate in a rarefied gas of spin-zero bosons. A rarefied gas of bosons is exposed to the static external field, which ensures its finite ground state. The derived equation allows one to correctly determine the ground state energy in the stationary case.

Spinning Black Holes Fall in Love.

The open question of whether a black hole can become tidally deformed by an external gravitational field has profound implications for fundamental physics, astrophysics, and gravitational-wave astronomy. Love tensors characterize the tidal deformability of compact objects such as astrophysical (Kerr) black holes under an external static tidal field. We prove that all Love tensors vanish identically for a Kerr black hole in the nonspinning limit or for an axisymmetric tidal perturbation. In contrast to this result, we show that Love tensors are generically nonzero for a spinning black hole. Specifically, to linear order in the Kerr black hole spin and the weak perturbing tidal field, we compute in closed form the Love tensors that couple the mass-type and current-type quadrupole moments to the electric-type and magnetic-type quadrupolar tidal fields. For a dimensionless spin ∼0.1, the nonvanishing quadrupolar Love tensors are ∼2×10^{-3}, thus showing that black holes are particularly "rigid" compact objects.

Frequency- and magnetic-field-dependent properties of ordered magnetic nanoparticle arrangements

We present investigations of the frequency and magnetic field dependent properties of ordered magnetic nanoparticles (MNPs) arrangements consisting of magnetite (${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$) nanoparticles with an average diameter of 20 nm by employing micro Brillouin light scattering microscopy. We utilized electron beam lithography to prepare hexagonally arranged, circularly shaped MNP assemblies consisting of a single layer of MNPs using a variant of the Langmuir-Blodgett technique. By comparing the results with nonstructured, layered superlattices of MNPs, further insight into the influence of size and geometry of the arrangement on the collective magnetic properties is obtained. We show that at low static external field strengths, two signals occur in frequency dependent measurements for both nonstructured and structured assemblies. Increasing the static external field strength results in a sharpening of the main signal, while the satellite signal decreases in its intensity and increases in its linewidth. The occurrence of multiple signals at low external field strengths is also confirmed by sweeping the static external field and keeping the excitation frequency constant. Furthermore, two-dimensional spatial mapping of the resonances reveals that the main and the satellite signal originate from the center and the edge, respectively, of a single circular MNP assembly. Micromagnetic simulations confirm these assignments and the dependence of the two signals on the static external field strength, justifying an interpretation of the observed characteristics in terms of different local environments of MNPs forming the MNP assembly.

Control of Light Transmission in a Plasmonic Liquid Metacrystal.

In this study, we experimentally demonstrated the control of light transmission through a slab of plasmonic liquid metacrystal by an external electric field. By applying the external static field, we were able to induce macroscopic anisotropy, which caused the polarization-dependent suppression of transmission at resonant frequencies. Such behavior indicates the selective plasmon excitation governed by the orientation of the meta-atoms with respect to the polarization of the electromagnetic wave. The problem of light transmission through a plasmonic liquid metacrystal was analyzed theoretically from first principles, and the obtained results were compared with the experimental data.

In silico assessment of collateral eddy current heating in biocompatible implants subjected to magnetic hyperthermia treatments

Purpose: Bearing partially or fully metallic passive implants represents an exclusion criterion for patients undergoing a magnetic hyperthermia procedure, but there are no specific studies backing this restrictive decision. This work assesses how the secondary magnetic field generated at the surface of two common types of prostheses affects the safety and efficiency of magnetic hyperthermia treatments of localized tumors. The paper also proposes the combination of a multi-criteria decision analysis and a graphical representation of calculated data as an initial screening during the preclinical risk assessment for each patient. Materials and methods: Heating of a hip joint and a dental implant during the treatment of prostate, colorectal and head and neck tumors have been assessed considering different external field conditions and exposure times. The Maxwell equations including the secondary field produced by metallic prostheses have been solved numerically in a discretized computable human model. The heat exchange problem has been solved through a modified version of the Pennes' bioheat equation assuming a temperature dependency of blood perfusion and metabolic heat, i.e. thermorregulation. The degree of risk has been assessed using a risk index with parameters coming from custom graphs plotting the specific absorption rate (SAR) vs temperature increase, and coefficients derived from a multi-criteria decision analysis performed following the MACBETH approach. Results: The comparison of two common biomaterials for passive implants - Ti6Al4V and CoCrMo - shows that both specific absorption rate (SAR) and local temperature increase are found to be higher for the hip prosthesis made by Ti6Al4V despite its lower electrical and thermal conductivity. By tracking the time evolution of temperature upon field application, it has been established that there is a 30 s delay between the time point for which the thermal equilibrium is reached at prostheses and tissues. Likewise, damage may appear in those tissues adjacent to the prostheses at initial stages of treatment, since recommended thermal thresholds are soon surpassed for higher field intensities. However, it has also been found that under some operational conditions the typical safety rule of staying below or attain a maximum temperature increase or SAR value is met. Conclusion: The current exclusion criterion for implant-bearing patients in magnetic hyperthermia should be revised, since it may be too restrictive for a range of the typical field conditions used. Systematic in silico treatment planning using the proposed methodology after a well-focused diagnostic procedure can aid the clinical staff to find the appropriate limits for a safe treatment window.