Change Of External Field Research Articles

Unveiling the role of external electric field on the charge transport and excited-state properties of high T1 host for blue OLED devices

Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were performed to understand the effect of the external electric field (EEF) on the reorganization (λ) and the lowest triplet excited-state (T1) energies of high T1 blue host materials. Depending on the direction and the strength of the external electric field (EEF), the positive and negative changes of hole and electron λ(h and λ e) values were found in these materials. More importantly, λ e seems to be more sensitive than λ h values under the EEF. It is also noticed that the calculated T1 energies are meaningfully changed in the application of EEFx and EEFy. In contrast, the effect of EEFz on the T1 energies can be negligible. From the results of theoretical investigation, the obvious evidence related to the influence of EEF on the charge transport and excited-state properties of high T1 blue host materials were obtained. In the present work, we expect that our theoretical study will provide new insight into understanding the influence of EEF as a key player in manipulating essential properties of the high T1 blue host material during the electrical operation.

Microstructure and magnetocaloric effect in nonequilibrium solidified Ni-Mn-Sn-Co alloy prepared by laser powder bed fusion

Additive manufacturing (AM) enables complex structures of Ni-Mn-X Heusler alloys to be utilized in solid state refrigeration systems. Here, the laser powder bed fusion (L-PBF) technique was used to fabricate a Ni-Mn-Sn-Co magnetic shape memory alloy with sophisticated geometries. Relative densities ranging from 96.12 to 97.04% were attained. L21–ordered austenite and an average structure of 5-layered modulated (5 M) martensite were observed at ambient temperature. The nonequilibrium solidification condition and repeated remelting processes during L-PBF gave rise to a strong 〈001〉A texture in austenite with epitaxial columnar grains along the build direction and dendrites related to microsegregation. Furthermore, the austenite exhibited nanodomains in its matrix and the martensite possessed stacking-mediated structures with 4–7 layers of atoms randomly stacked within the twin substructures. The combined influence of relatively homogeneous composition and specific microstructures yielded a competitive magnetization difference of 81.0 A·m2·kg–1 and a maximum magnetic entropy change of about 14 J·kg–1·K–1 with a working temperature interval of about 22 K under the external field change of 5.0 T without any heat treatment. The as-built state alloy is expected to facilitate the development of new laser AM techniques for Ni-Mn-X alloys.

Phononic-Crystal-Based SAW Magnetic-Field Sensors.

In this theoretical study, we explore the enhancement of sensing capabilities in surface acoustic wave (SAW)-based magnetic field sensors through the integration of engineered phononic crystals (PnCs). We particularly focus on amplifying the interaction between the SAW and magnetostrictive materials within the PnC structure. Through comprehensive simulations, we demonstrate the synchronization between the SAWs generated by IDTs and the resonant modes of PnCs, thereby leading to an enhancement in sensitivity. Furthermore, we investigate the ΔE effect, highlighting the sensor's responsiveness to changes in external magnetic fields, and quantify its magnetic sensitivity through observable changes in the SAW phase velocity leading to phase shifts at the end of the delay line. Notably, our approach yields a magnetic field sensitivity of approximately S~138 °mT for a delay line length of only 77 µm in homogeneous magnetic fields. Our findings underline the potential of PnCs to advance magnetic field sensing. This research offers insights into the integration of engineered materials for improved sensor performance, paving the way for more effective and accurate magnetic field detection solutions.

Multiscale modeling of Na2WO4–WO3–CoO melt diffusion layer for molecular dynamics combined with finite element analysis

In the process of molten salt electrolysis of spent tungsten carbide for the separation of tungsten and cobalt, the nature of the molten salt has a crucial impact on product quality and efficiency. In this study, the microscopic and macroscopic models of the diffusion layer of Na2WO4–WO3–CoO molten salt were developed. The structure, transport properties and electroanalytical behavior of Na2WO4–WO3–CoO molten salt were investigated by combining molecular dynamics and finite element simulation under different CoO and WO3 molar ratios and different applied electric field conditions. The cost of this approach is relatively low compared to experiments. It was found that the addition of CoO hinders the mass transfer and increases the electrochemical impedance. The reason for this is that the addition of CoO leads to an increase in the entropy of the molten salt. The change in external electric field does not affect this law. The calculated results are in general agreement with the available experimental data. In the study of the structure of molten salts, the vacancy volume factor, which is a metric for evaluating the size of the vacancy volume of molten salts, was proposed for the first time. The addition of CoO also affects the microstructure, which can be used to infer changes in the electrodeposition products. Experimental results of electrodeposition support this speculation. This study confirms that a combination of macroscopic and microscopic, molecular dynamics and finite element simulations can theoretically aid the development of molten salt electrolysis processes.

Unraveling the Complex Interplay of Phase Transitions in Spinel Ferrites: A Comprehensive Quantum Mechanical Vibrational Study of ZnFe2O4.

The rich phase transition landscape of spinel ferrites and its profound impact on their physical properties have garnered significant interest in recent years. The complex interplay of divalent and trivalent cations distributed across A- and B-sites gives rise to a captivating variety of interactions. In this study, we delve into the structural, electronic, magnetic, and vibrational properties of ZnFe2O4 as a function of the degree of inversion, employing first-principles density functional theory with global and range-separated hybrid functionals and a local basis set. The ground state of ZnFe2O4 is an open-shell system, characterized by Zn atoms occupying tetrahedral sites, Fe atoms residing in octahedral sites, and Fe atom spins exhibiting ligand parallel alignment. In the normal structure, the antiparallel arrangement is less stable than the ferro arrangement by 0.058 eV (673 K) for fully relaxed structures, decreasing to 0.034 eV (395 K) upon incorporating a zero-point vibrations contribution. For normal ferromagnetic ZnFe2O4, we calculated scattering for A1g, Eg, and 3T2g symmetry at 676.6, 367.1, and (189.7, 457.7, 602.3) cm-1, respectively. Additionally, four T1u vibrational frequencies predicted by group theory were obtained at 524.59, 358.48, 312.49, and 192.9 cm-1, demonstrating excellent agreement with the experimental studies. We also explored the influence of spin rearrangement and inversion (X = 0.5 and 1) on Raman and infrared spectra. By analyzing the infrared spectra of isotopic substitutions, we reevaluated the assignments of the four T1u modes in light of available experimental data. Notably, the sensitivity of peak positions and intensities for some Raman modes, particularly A1g and T2g(2), to spin arrangement could provide a convenient experimental tool for detecting phase transitions induced by changes in temperature or external electric fields. This investigation shines a light on the complex interplay of phase transitions in spinel ferrites, paving the way for a deeper understanding of their properties and potential applications.

Tunable electrical contact properties in two-dimensional van der Waals V2C/MoSi2N4 heterostructures

Two-dimensional MoSi2N4 is a member of the emerging 2D MA2N4 family, which has been synthesized in experiments, recently. Herein, we conduct a first-principles investigation to study more about the atomic and electronic structures of V2C/MoSi2N4 (1T-phase) van der Waals heterostructures (vdWHs) and interlayer distance and an external perpendicular electric field change their tunable electronic structures. We demonstrate that the V2C/MoSi2N4 vdWHs contact forms n-type Schottky contact with an ultralow Schottky barrier height of 0.17 eV, which is beneficial to enhance the charge injection efficiency. In addition, the electronic structure and interfacial properties of V2C/MoSi2N4 vdWHs can be transformed from n-type to p-type ShC through the effect of layer spacing and electric field. At the same time, the transition from ShC to OhC can also occur by relying on the electric field and different interlayer spacing. Our findings could give a novel approach for developing optoelectronic applications based on V2C/MoSi2N4 vdW heterostructures.

The second, third harmonic generations and nonlinear optical rectification of the Mathieu quantum dot with the external electric, magnetic and laser field

In this study, the nonlinear optical properties of the InxGa1−xAs/GaAs Mathieu quantum dot (MQD) are investigated for the first time, focusing on the nonlinear optical rectification (NOR), second harmonic generation (SHG), and third harmonic generation (THG). The effects of external fields such as the electric field, magnetic field, and laser radiation field on the nonlinear optical properties of MQD are examined, along with structural parameters such as quantum dot depth and width determined by the indium concentration. The motivation of the study is to explain the NOR, SHG, and THG characteristics of MQD in response to changes in external fields and structural factors. To investigate the effects of the laser field, the time-dependent part of the laser field is transferred to the potential energy term of the wave equation using the Kramers–Henneberger (KH) and dipole approximations, creating a laser-dressed potential. Then, the effective potential wave equation is solved using the tridiagonal matrix method. The effects of external fields and structural parameters of MQD on the NOR, SHG, and THG coefficients are discussed in detail. The optimality of the structure for device design and applications considering MQD is revealed, and alternative parameter analysis is conducted for this optimality.

Landau levels and snake states of pseudo-spin-1 Dirac-like electrons in gapped Lieb lattices

This work reports the three-band structure associated with a Lieb lattice with arbitrary nearest and next-nearest neighbors hopping interactions. For specific configurations, the system admits a flat band located between two dispersion bands, where three inequivalent Dirac valleys are identified. Furthermore, quasi-particles are effectively described by a spin-1 Dirac-type equation. Under external homogeneous magnetic fields, the Landau levels are exactly determined as the third-order polynomial equation for the energy can be solved using Cardano’s formula. It is also shown that an external anti-symmetric field promotes the existence of current-carrying states, so-called snake states, confined at the interface where the external field changes its sign.

Multicaloric effect in Ni–Mn–Sn metamagnetic shape memory alloys by laser powder bed fusion

Metamagnetic shape memory alloys with giant caloric effects and sophisticated geometries are promising candidates for solid-state refrigeration. Additive manufacturing (AM) overcomes the machining difficulties and may provide the geometric freedom. Whereas the metallurgical defects in AM limits their applications, and the multicaloric effects of AM metamagnetic shape memory alloys have been poorly understood. Here, Ni 45 Mn 44 Sn 11 metamagnetic shape memory alloys are prepared via laser powder bed fusion ( L -PBF). A magnetic entropy change of 10.2 J kg −1 K −1 and adiabatic temperature change of 0.8 K is achieved under the external field change of 5 T and 1.5 T, respectively. An improved relative density of ∼99.5% and high compressive strength of 519 MPa is achieved. These result from the defects mitigation which shows homogeneous grain structure/composition and crack healing during rapid printing and subsequent annealing. Particularly, we have proposed a multicaloric approach of “magnetic-field-assisted elastocaloric cooling” to enhance the temperature change up to 7.4 K, which is 20% higher than the sole elastocaloric effect. These results provide a basis for future studies of the multicaloric effect in metamagnetic shape memory alloys fabricated via AM.

Investigation on electronic properties modulation of vdW GaN/WSe2 heterostructure by electric field

In this paper, we designed two van der Waals (vdW) GaN/WSe2 heterostructures based on the GaN and WSe2 monolayers. And then we further investigated the effect of the external electric field on electronic properties of the more stable GaN/WSe2 vdW heterostructure by first-principle calculations. Results show that without external electric field, the GaN/WSe2 is a typical type-I band alignment heterostructure. But both the VBO and CBO are smaller than 1 eV, which limits their application in electric devices. So we further adopt an external electric field to adjust the electronic properties of the heterostructure. Results show that when applying an external electric field of [Formula: see text] V/Å, the band alignment of GaN/WSe2 heterostructure changes from type-I to type-II, and the electrons and holes are separated into different layers. Then the recombination of the holes and electrons is blocked and the lifetime of photo-induced carriers can be prolonged. To understand the inherent physical mechanism, the variation trends of the band gap and band offset as the change of external electric field were discussed. Results show that the location and contribution factors of conduction band minimum (CBM) and valence band maximum (VBM) caused by external electric field are the main factors causing this change in the heterostructure.

Molecular sensors producing circularly polarized luminescence responses

Circularly polarized luminescence (CPL) refers to spontaneous emission with the oscillation axis of the emission's electric dipole rotating either right handedly or left handedly along the propagation axis. CPL provides a unique principle in luminescence visualization of target analytes: both the direction and magnitude of light polarization are sensitive to an asymmetric environment around a luminophore, which enables chirality sensing. In addition, CPL spectra are usually less complex than electric circular dichroism spectra because they emerge only from the lowest excited state. To exploit these benefits, researchers have vigorously developed CPL probes. This minireview provides the basic principles for creating molecular CPL activity, including asymmetric exciton coupling and helical intramolecular charge transfer. Emphasis is placed on molecular design. Analyte interactions can perturb the magnitude, reverse the polarization direction, or shift the peak wavelength of CPL, thereby enabling tractable strategies for creating CPL sensors. This minireview outlines selected examples of CPL sensors for physical stimuli, including changes in external magnetic fields, solvent polarity, and temperature. Probes capable of detecting chemical species, such as protons, metal ions, anions, amino acids, nucleosides and DNA, reactive oxygen species, and humidity, are also highlighted. These examples demonstrate the unique sensing utility of CPL sensors. We hope that this minireview will stimulate future research interest toward developing advanced CPL sensors with applications in bioimaging.

Enhanced near-ambient temperature energy storage and electrocaloric effect in the lead-free BaTi0.89Sn0.11O3 ceramic synthesized by sol–gel method

Lead-free perovskite materials with high performance have high potential in clean energy storage applications and developments of electrocaloric devices. This work reports structural, dielectric, ferroelectric, energy storage, and electrocaloric properties near the ambient temperature in barium stannate titanate (BaTi0.89Sn0.11O3, BTS11) ceramic prepared by a sol–gel method. A single perovskite structure formation was confirmed using the X-ray diffraction analysis. Average grain size of 18.5 µm was found by the mean of the SEM micrograph with a density of 5.91 g/cm3. The multiphase coexistence at very near ambient temperature was proved using temperature-dependent micro-Raman measurements and differential scanning calorimetry. The BTS11 ceramic exhibits a high dielectric constant of 15,460 and a low dielectric loss (< 0.055) in a broad temperature range. Moreover, a high energy storage density of 122 mJ/cm3 was shown with an efficiency of 79%, a maximum value of electrocaloric temperature change (ΔT) of 0.86 K, and finally, an electrocaloric responsivity (ΔT/ΔE) of 0.24 K.mm/kV at the external electric field change of 35 kV/cm near ambient temperature. The enhanced dielectric, ferroelectric, and electrocaloric properties make BTS11 ceramics a great candidate for solid-state cooling technology and high energy storage applications near ambient temperature.

Magnetically Steerable Serial and Parallel Structures by Mold‐Free Origami Templating and Domain Setting

AbstractMagnetically responsive elastomers generate continuous motions and locomotion through changes in external magnetic fields. The magnetic particles in an elastomer achieve shape‐morphing, but overall structural integrity can be limited by the compliance of elastomers. To overcome this limitation, magnetic elastomers are enhanced with programmable template creases to generate deployable structures as a library. Current methods to program magnetic domains into actuatable segments use sequential or continuous rasterized magnetization, which is gradual and requires dedicated equipment. To achieve faster magnetic domain programming, template folding for the magnetization process is explored. The crease pattern can reconfigure facets to attain the desired magnetization direction and act as discrete mechanical joints. Crease patterns from the foldable templates allow more variations in robotic kinematics and discretize the deformations. The approach using magnetic elastomers and folding templates as a library can simultaneously program a wide range of deployable mechanisms with inherent crease foldability. Additionally, magnetic responsive robots can encompass bistable actuation imparted from the crease design. Functionalization of magnetic origami structures is demonstrated by imbuing the template material with catalytic properties. These robots have the potential to be deployed from a compact folded form to confined environments, enabling a broader spectrum of minimally invasive procedures.

Guest-Mediated Hierarchical Self-Assembly of Dissymmetric Organic Cages to Form Supramolecular Ferroelectrics

Guest-Mediated Hierarchical Self-Assembly of Dissymmetric Organic Cages to Form Supramolecular Ferroelectrics

Design and experiment of piezoelectric-shape memory alloy composite shock absorber

Piezoelectric material is one of the most widely used intelligent materials, which can produce strain according to the change of external electric field. Shape memory alloy material is also a widely used smart material, which has a large hysteresis damping characteristic. We combine the advantages of piezoelectric materials and shape memory alloy materials, and firstly propose a new kind of shock absorber. The damping effect of the number and arrangement of shape memory alloy wires have been studied, and then the control strategy of piezoelectric ceramics on the vibration reduction effect of the structure are verified by experimental methods.

Magnetic proximity effect induced spin splitting in two-dimensional antimonene/Fe3GeTe2 van der Waals heterostructures

Recently, two-dimensional van der Waals (vdW) magnetic heterostructures have attracted intensive attention since they can show remarkable properties due to the magnetic proximity effect. In this work, the spin-polarized electronic structures of antimonene/Fe3GeTe2 vdW heterostructures were investigated through the first-principles calculations. Owing to the magnetic proximity effect, the spin splitting appears at the conduction-band minimum (CBM) and the valence-band maximum (VBM) of the antimonene. A low-energy effective Hamiltonian was proposed to depict the spin splitting. It was found that the spin splitting can be modulated by means of applying an external electric field, changing interlayer distance or changing stacking configuration. The spin splitting energy at the CBM monotonously increases as the external electric field changes from –5 V/nm to 5 V/nm, while the spin splitting energy at the VBM almost remains the same. Meanwhile, as the interlayer distance increases, the spin splitting energies at the CBM and VBM both decrease. The different stacking configurations can also induce different spin splitting energies at the CBM and VBM. Our work demonstrates that the spin splitting of antimonene in this heterostructure is not singly dependent on the nearest Sb–Fe distance, which indicates that magnetic proximity effect in heterostructures may be modulated by multiple factors, such as hybridization of electronic states and the local electronic environment. The results enrich the fundamental understanding of the magnetic proximity effect in two-dimensional vdW heterostructures.

Giant volume magnetostriction in La0.85Ce0.15Fe12B6

We report the discovery of giant magnetostriction and huge negative thermal expansion (NTE) in the itinerant-electron metamagnetic compound La0.85Ce0.15Fe12B6. This system presents multiple magnetic transformations, antiferromagnetic–ferromagnetic (AFM–FM) and ferromagnetic–paramagnetic (FM–PM), driven by changes in both external field and temperature. The magnetic-field–dependent magnetostriction exhibits irreversible abrupt jumps at T ≤ 5 K, while it evolves smoothly with applied field above 5 K. A giant positive volume magnetostriction of ΔV/V (20 K, 6 T) = 0.80% is observed across the field-induced first-order AFM–FM metamagnetic transition. It is further revealed that the FM–PM transition is accompanied by a remarkably large NTE with a coefficient of linear thermal expansion αL = −34 × 10−6 K−1 over a temperature window of ΔT ∼ 63 K.

Electrogyration in Metamaterials: Chirality and Polarization Rotatory Power that Depend on Applied Electric Field

AbstractOne of the most fascinating properties of chiral molecules is their ability to rotate the polarization of light. Since Faraday's experiments in 1845, it has been known that nonreciprocal polarization rotatory power can be induced by a magnetic field. But can reciprocal polarization rotation in chiral molecules be influenced by an electric field? In the 1960s, Aizu and Zheludev introduced the phenomenon of electrogyration. While the linear (Pockels) and quadratic (Kerr) electro‐optical effects describe how an external electric field changes linear birefringence and dichroism, electrogyration describes how a field changes the circular birefringence and dichroism of a medium. Electrogyration is observed in dielectrics, semiconductors, and ferroelectrics, but the effect is small. This work demonstrates a nanostructured photonic metamaterial that exhibits quadratic electrogyration—proportional to the square of the applied electric field—six orders of magnitude stronger than in any natural medium. Giant quadratic electrogyration emerges as electrostatic forces acting against forces of elasticity change the chiral configuration of the metamaterial's nanoscale building blocks and consequently its polarization rotatory power. This observation of giant electrogyration alters the perception of the effect from that of an esoteric phenomenon into a functional part of the electro‐optic toolkit with application potential.

Magnetically induced elastic deformations in model systems of magnetic gels and elastomers containing particles of mixed size

Soft elastic composite materials can serve as actuators when they transform changes in external fields into mechanical deformation. Here, we theoretically address the corresponding deformational behavior in model systems of magnetic gels and elastomers exposed to external magnetic fields. In reality, such materials consist of magnetizable colloidal particles in a soft polymeric matrix. Since many practical realizations of such materials involve particulate inclusions of polydisperse size distributions, we concentrate on the effect that mixed particle sizes have on the overall deformational response. To perform a systematic study, our focus is on binary size distributions. We systematically vary the fraction of larger particles relative to smaller ones and characterize the resulting magnetostrictive behavior. The consequences for systems of various different spatial particle arrangements and different degrees of compressibility of the elastic matrix are evaluated. In parts, we observe a qualitative change in the overall response for selected systems of mixed particle sizes. Specifically, overall changes in volume and relative elongations or contractions in response to an induced magnetization can be reversed into the opposite types of behavior. Our results should apply to the characteristics of other soft elastic composite materials like electrorheological gels and elastomers when exposed to external electric fields as well. Overall, we hope to stimulate corresponding experimental realizations and the further investigation on the purposeful use of mixed particle sizes as a means to design tailored requested material behavior.

Entanglement dynamics of two coupled spins interacting with an adjustable spin bath: effect of an exponential variable magnetic field

The present work is devoted to studying the entanglement dynamics of two central spins coupled in a spin environment and subjected, simultaneously, to an external magnetic field changing with time t as an exponential function $${\mathfrak {B}}\left( 1-\mathrm{e}^{-\lambda t}\right) $$ . We want to determine whether interaction among central spins with an external magnetic field as well as preparation of bath in an appropriate spin coherent state, $$|\beta \rangle _\mathrm{{bath}}$$ , is shown to affect the decoherence process in a qualitatively significant manner. We show that the dynamics of the entanglement depends on the initial state of the central spins as well as the bath, the coupling constants and the strength of a magnetic field, $${\mathfrak {B}}, \lambda $$ . Compared with some cases already discussed in the literature as magnetic fields of periodic $$\sin (\lambda t)$$ and $$\cos (\lambda t)$$ functions, we can see that a magnetic field of exponential function $$\mathrm{e}^{-\lambda t}$$ plays a very crucial role in the entanglement generation between the two-spin qubits and its protection. To do this, we use an operator technique of the Holstein–Primakoff transformation, and the dynamics of the reduced density matrix of two coupled spin qubits is obtained in both finite and infinite numbers of bath spins. We also derive the concurrence measure to quantify the entanglement of the reduced density matrix of the two coupled central spins and look for conditions that provide information on whether this becomes robust against decoherence. It has been shown that the entanglement distribution can be both amplified, stabilized and protected with $${\mathfrak {B}}, \lambda $$ and $$\beta $$ . These results motivate developments toward the implementation or simulation of the purely theoretical model employing exponential fields.