AC Field Strength Research Articles

Effects of frequency mixing on Shapiro-step formations in sliding charge-density-waves

A one-dimensional charge-density wave (CDW) is driven to slide by a dc electric field, carrying an electric current. In an additional ac field with frequency ωex, it is known that the sliding CDW can be synchronized to ωex, leading to the occurrence of Shapiro steps in the I–V characteristics. Motivated by a recent experiment where ac fields with two frequencies ωex and ωex′ are simultaneously applied, we theoretically investigate the effects of frequency mixing on the Shapiro-step formation. Based on the Fukuyama–Lee–Rice model, we show that in addition to the main steps induced by ωex, satellite steps characterized by ωex′ emerge. It is also found that with increasing the ac-field strength for ωex′, each step width first exhibits a damped oscillation as in the one-frequency case and then exhibits a non-monotonic behavior. The origin of these behaviors and the relevance to the associated experiment are also discussed.

Rapid millisecond heating via ferromagnetic resonance in MnFe2O4 nanoparticles

This study undertakes an exhaustive analysis of rapid heat generation in MnFe2O4 nanoparticles through ferromagnetic resonance within an ultra-fast timeframe of 1 ms. Real-time monitoring of temperature during single-field-pulse excitations provided detailed insights into the temperature rise profiles. By integrating micromagnetic simulations with analytical modeling—taking into account both convective and radiative losses—we have deepened our understanding of the heat transfer dynamics at play. Adjusting the analytical model to align with experimental temperature profiles enabled us to determine the efficiency of converting spin dissipation energy into heat, which stands at 17%. This figure reflects not only the surface area of the nanoparticles but also includes considerations for radiative and convective losses. Notably, employing a low AC-field strength of 17.6 Oe facilitated a rapid temperature increase of up to 90 K in just 0.5 s, showcasing a peak initial temperature rise rate of approximately 680 K/s. This research advances the frontiers of high-power heat generation driven by spin dynamics and provides a comprehensive exploration of heat transfer mechanisms over exceptionally short pulse durations. These findings could revolutionize precise and rapid temperature management at the nanoscale, unlocking prospects in bio applications, accelerated material processing, and inducing color and phase shifts in polymer matrices.

Transparent qubit manipulations with spin-orbit coupled two-electron nanowire quantum dot

We report on the first set of exact orthonormalized states to an ac driven one-dimensional (1D) two-electron nanowire quantum dot with the Rashba–Dresselhaus coexisted spin-orbit coupling (SOC) and the controlled magnetic field orientation and trapping frequency. In the ground state case, it is shown that the spatiotemporal evolutions of probability densities occupying internal spin states and the transfer rates between different spin states can be adjusted by the ac electric field and the intensities of SOC and magnetic field. Effects of the system parameters and initial-state-dependent constants on the mean entanglement are revealed, where the approximately maximal entanglement associated with the stronger SOC and its insensitivity to the initial and parametric perturbations are demonstrated numerically. A novel resonance transition mechanism is found, in which the ladder-like time-evolution process of expected energy and the transition time between two arbitrary exact states are controlled by the ac field strength. Using such maximally entangled exact states to encode qubits can render the qubit control more transparent and robust. The results could be extended to 2D case and to an array of two-electron quantum dots with weak neighboring coupling for quantum information processing.

Difference in AC magnetization between suspended and immobilized magnetic nanoparticles in Néel-relaxation dominant case: Effect of easy axis alignment in suspended nanoparticles

Magnetic nanoparticles (MNPs) have been widely studied for bio-sensing applications, where suspended and immobilized MNPs can be magnetically distinguished using their different magnetic properties. We study magnetic properties of suspended and immobilized MNPs when the Néel relaxation time is much shorter than the Brownian. We show in both numerical simulation and experiment that they have different magnetic properties such as AC magnetization curves and harmonic spectra even though the dynamic behavior of both MNP types is primarily dominated by Néel relaxation. This difference is caused by the partial alignment of the easy axes in suspended MNPs when an AC magnetic field is applied. We introduce a distribution function for the angle of easy axis alignment. We also show a method to evaluate the distribution function from the measured AC magnetization curve and clarify the relationship between easy axis alignment and the AC field strength. Using the distribution function, we can quantitatively discuss the effect of easy axis alignment on the magnetic properties of suspended MNPs. The obtained results provide a basis for using MNPs in bio-sensing.

Effects of Inorganic ZnO Particle Doping on Crystalline Polymer Morphology and Space Charge Behavior

This study further investigated the synergistic effect of micro- and nanofiller doping on matrix material space charges and breakdown characteristics. Accordingly, low-density polyethylene (LDPE) was used as the matrix material, and spherical ZnO particles with sizes of 30 nm and 1 µm were used as additives. Micro-ZnO/LDPE, nano-ZnO/LDPE, and micro-nano-ZnO/LDPE composites were prepared through melt blending. The crystalline morphologies of the composites were observed via polarized light microscopy. The composite crystallinity and melting peak temperature were measured via differential scanning calorimetry, and the micro- and nanoparticle dispersions in the matrix were observed via scanning electron microscopy. The test results showed that the particles were uniformly dispersed in the polyethylene matrix. The filler acted as a heterogeneous nucleation agent in the matrix. The crystal size decreased, thereby increasing the crystal quantity. The doping of inorganic ZnO particles improved the composite crystallinity. The ZnO/LDPE composites were subjected to DC breakdown, space charge, and dielectric spectrum tests. When the crystal arrangement of the sample was loose and its size was large, the breakdown process developed along a shorter path, and the field strength of the composite breakdown decreased. The order of AC and DC breakdown field strengths of the samples was as follows: micro-ZnO/LDPE < pure LDPE < micro-nano-ZnO/LDPE < nano-ZnO/LDPE. The DC and AC breakdown field strengths of the micro- and nano-ZnO/LDPE were 4.7% and 3.2% higher than those of the pure LDPE, respectively. Moreover, the DC and AC breakdown field strengths of the nano-ZnO/LDPE were 11.02% and 15.8% higher than those of the pure LDPE, respectively. The doping of inorganic ZnO particles restrained the space charge accumulation, and the residual charges decreased after short-circuit treatment. The dielectric constant of all nanocomposites was lower than that of LDPE, and the dielectric loss of all composites was higher than that of LDPE.

Magnetotransport through ac driven ferromagnetic graphene nanoribbons

We present a theoretical study on the spin-dependent transport through the ferromagnetic graphene nanoribbons in the presence of a magnetic and an in-plane ac electric field, and find that when the ac field is applied, in the two-terminal ferromagnetic graphene device, for the parallel configurations of the electrodes' magnetizations, the width of the even-number conductance plateaus decrease, the new conductance plateaus appear at the odd-number positions, and the even-number conductance plateaus at the high energy are quenched under the sufficiently strong ac field. In contrast, for the antiparallel configuration of the electrodes' magnetizations, the odd-plateaus of the conductance shrink, and the new plateaus developed at the even-number positions. The magnetic resistance exhibits a successive rectangular-like oscillation structure close to the band edge, whereas experiences an alternative transition between the sharp peak and dip near the zero energy with increasing the ac field strength. In the six-terminal ferromagnetic graphene device, the variations of the longitudinal and Hall resistances' plateaus as well as the addition of the new quantized plateaus with the rise of the ac field strength are also revealed.

Forced response and dynamic hysteresis of magnetic nanoparticles with mixed uniaxial and cubic anisotropy in superimposed strong ac and dc bias fields

The stationary response of ferromagnetic nanoparticles with mixed uniaxial and cubic anisotropy to superimposed external ac and dc bias fields of arbitrary strength is investigated using Brown's continuous diffusion of orientations model [W. F. Brown Jr., Phys. Rev. 130, 1677 (1963)]. The susceptibility and dynamic magnetic hysteresis (DMH) loops of an individual nanoparticle are calculated in extensive ranges of the superimposed fields, their orientation, damping, temperature, and specific mixed anisotropy parameter. The DMH loops and nonlinear dynamic susceptibility strongly depend on the dc and ac field strengths, the polar angle between the easy axis of the particle and the external field vectors, as well as the temperature and damping, simultaneously displaying a marked dependence on the mixed anisotropy parameter.

Transient Dynamics of Super Bloch Oscillations of a 1D Holstein Polaron under the Influence of an External AC Electric Field

AbstractTheoretical formalism for DC‐field polaron dynamics is extended to the dynamics of a 1D Holstein polaron in an external AC electric field using multiple Davydov trial states. Effects of carrier–phonon coupling on detuned and resonant scenarios are investigated for both phase and nonzero phase. For slightly off‐resonant or detuned cases, a beat between the usual Bloch oscillations and an AC driving force results in super Bloch oscillations, that is, rescaled Bloch oscillations in both the spatial and the temporal dimension. Super Bloch oscillations are damped by carrier–phonon coupling. For resonant cases, if the carrier is created on two nearest‐neighboring sites, the carrier wave packet spreads with small‐amplitude oscillations. Adding carrier–phonon coupling localizes the carrier wave packet. If an initial broad Gaussian wave packet is adopted, the centroid of the carrier wave packet moves with a certain velocity and with its shape unchanged. Adding carrier–phonon coupling broadens the carrier wave packet and slows down the carrier movement. Our findings may help provide guiding principles on how to manipulate the dynamics of the super Bloch oscillations of carriers in semiconductor superlattice and optical lattices by modifying DC and AC field strengths, AC phases, and detuning parameters.

Photoassisted transport in silicon dangling bond wires

We theoretically investigate charge transport through dangling bond (DB) nanostructures built on a passivated silicon (100) surface by selectively removing hydrogen atoms. We focus on dangling bond wires and on T-junctions. In the latter case, destructive quantum interference effects lead to a strong suppression of charge transport mediated by the DB electronic states. We demonstrate, however, that by applying a time periodic voltage, mimicking irradiation with monochromatic light, a dramatic enhancement of the current up to the μA range can be achieved. This result is however limited by the restriction on the AC field strength and frequency that bulk states should minimally contribute to charge transport; otherwise current leakage will set in. Despite this constraint, transconductance values of the order of 10−6 A/V can be achieved, illustrating the potential of the discussed systems to find applications in nanoscale electronics.

Effect of viscosity on harmonic signals from magnetic fluid

We explored the effect of viscosity on harmonic signals from a magnetic fluid. Using a numerical simulation that accounts for both the Brownian and Neel processes, we clarified how the magnetization mechanism is affected by viscosity. When the excitation field varies much slower than the Brownian relaxation time, magnetization can be described by the Langevin function. On the other hand, for the case when the excitation field varies much faster than the Brownian relaxation time, but much slower than the Neel relaxation time, the easy axes of the magnetic nanoparticles (MNPs) turn to some extent toward the direction of the excitation field in an equilibrium state. This alignment of the easy axes of MNPs caused by the AC field becomes more significant with the increase of the AC field strength. Consequently, the magnetization is different from the Langevin function even though Neel relaxation time is faster than time period of the external frequency. It is necessary to consider these results when we use harmonic signals from a magnetic fluid in a high-viscosity medium.

Nonlinear susceptibility and dynamic hysteresis loops of magnetic nanoparticles with biaxial anisotropy

The nonlinear ac susceptibility and dynamic magnetic hysteresis (DMH) of a single domain ferromagnetic particle with biaxial anisotropy subjected to both external ac and dc fields of arbitrary strength and orientation are treated via Brown's continuous diffusions model [W. F. Brown, Jr., Phys. Rev. 130, 1677 (1963)] of magnetization orientations. The DMH loops and nonlinear ac susceptibility strongly depend on the dc and ac field strengths, the polar angle between the easy axis of the particle, the external field vectors, temperature, and damping. In contrast to uniaxial particles, the nonlinear ac stationary response and DMH strongly depend on the azimuthal direction of the ac field and the biaxiality parameter Δ.

Micromagnetic Study of Microwave-Assisted Magnetization Reversals of Exchange-Coupled Composite Nanopillars

Microwave-assisted magnetization reversals of exchange-coupled composite nanopillars were studied by micromagnetic simulation. Magnetization reversal occurred in one or two frequency regions associated with magnetic resonance arising from the soft magnetic section. Significant reductions in ac field strength and frequency, which are required for magnetization switching, were obtained in cases where there was a large interface exchange constant between the soft and hard sections. It was also found that the large saturation magnetization of the soft magnetic section tends to enhance magnetization switching.

The Effect of Y2O3 on AC Susceptibility Measurements of MPMG YBCO Superconductor

In this study, two kinds of melt-powder-melt-growth (MPMG) YBCO sample grown on a buffer layer of Y2O3 addition were fabricated. The compacted powders were located on a crucible with Y2O3 powder freely poured and a buffer layer of pressed Y2O3. AC susceptibility measurements of the samples as a function of temperature was reported for several different AC magnetic-field amplitudes (Hac) in the presence of static bias magnetic field (Hb) directed along Hac. The loss peaks are found to shift towards lower temperatures as the AC field strength is increased. The frequency effect on the AC susceptibility was also measured. As the frequency increases, the peak temperature shifts to higher temperature. This effect can be interpreted in terms of flux creep.

Fiber-Optic Electric Field Sensor Based on Electrostriction Effect

This paper presents a new method for measuring AC field strength, with application of electrostriction effect of electrostrictive ceramics and technology of fiber Bragg grating. We use electrostriction effect to design the fiber-optic electric field sensor. This device turns the strain of electrostriction material influenced by electric field into the strain of fiber Bragg grating, then wavelength of feedback changes. We can get the strain of electrostriction material through the comparison between initial wavelength and wavelength of feedback, then measurement of electric field strength can be achieved by detecting the strain of electrostriction material. Experiments indicate that fiber-optic electric field sensor based on electrostriction effect is of effective value for measuring electric field strength, and the response of measuring system to AC electric field is linear. We apply an effective method for the research of measuring electric field strength.

Experimental Study on the Iron Loss Curve at High Field Strength of Non-Oriented Electrical Steel Sheet

At high AC field strength, BH loop tends to twist slightly near the tip point. It results in apparent decrease of iron loss because the overturned parts introduce negative iron loss value. In order to correct this error the phase difference between flux density and magnetic field strength needs to be eliminated. We studied on the problem and got satisfactory results.

Manipulating single annealed polyelectrolyte under alternating current electric fields: Collapse versus accumulation

Effective manipulation and understanding of the structural and dynamic behaviors of a single polyelectrolyte (PE) under alternating current (AC) electric fields are of great scientific and technological importance because of its intimate relevance to emerging bionanotechnology. In this work, we employ fluorescence correlation spectroscopy (FCS) to study the conformational and AC-electrokinetic behaviors of a model annealed PE, poly(2-vinyl pyridine) (P2VP) under both spatially uniform and non-uniform AC fields at a single molecule level. Under spatially uniform AC-fields, we observe a gradual and continuous coil-to-globule conformational transition (CGT) of single P2VP at varied AC-frequency when a critical AC-field strength is exceeded, in contrast to the pH-induced abrupt CGT in the absence of AC-fields. On the contrary, under spatially non-uniform AC-fields, we observe field-driven net flow and accumulation of P2VP near high AC-field regions due to combined AC electro-osmosis and dielectrophoresis but surprisingly no conformational change. Thus, distinct AC-electric polarization effect on single annealed PE subject to AC-field homogeneity is suggested.

Surfactant-free dielectrophoretic deposition of multi-walled carbon nanotubes with tunable deposition density

The effects of AC field strength and AC frequency on the density of dielectrophoretically deposited multi-walled carbon nanotubes (MWCNTs) were investigated and explained in terms of existing theory. We show that while both parameters can be used to control deposition density, the experimentally observed frequency trend can not be explained by the theoretical Clausius–Mossotti factors. We demonstrate the ability to make surfactant-free dispersions of long, difficult to disperse MWCNTs and use them with dielectrophoresis to make clean, single and few connections between electrodes.

A theoretical study of harmonic generation in a short period AlGaN/GaN superlattice induced by a terahertz field

Based on an improved energy dispersion relation, the terahertz field induced nonlinear transport of miniband electrons in a short period AlGaN/GaN superlattice is theoretically studied in this paper with a semiclassical theory. To a short period superlattice, it is not precise enough to calculate the energy dispersion relation by just using the nearest wells in tight binding method: the next to nearest wells should be considered. The results show that the electron drift velocity is 30% lower under a dc field but 10% higher under an ac field than the traditional simple cosine model obtained from the tight binding method. The influence of the terahertz field strength and frequency on the harmonic amplitude, phase and power efficiency is calculated. The relative power efficiency of the third harmonic reaches the peak value when the dc field strength equals about three times the critical field strength and the ac field strength equals about four times the critical field strength. These results show that the AlGaN/GaN superlattice is a promising candidate to convert radiation of frequency ω to radiation of frequency 3ω or even higher.

Electrochemical etching technique for neutron dosimetry

In the present work we have employed allyl diglycol carbonate (CR-39) and cellulose triacetate (CTA) plastic for detection of neutron recoil tracks without radiator. For CR-39, the results reveal that registration efficiency is a function of duration of chemical pre-etching and the best results are obtained with chemical pre-etching of 3 hours. It was also investigated that the ac field strength of 28 kV/cm having 2.5 kHz frequency was optimum for revelation of tracks. Interestingly the sensitivity is fluence dependent and it was constant up to a fluence of about 108 n/cm2. The sensitivity abruptly decreased with increased fluence. At optimum experimental conditions the minimum detection limit for CR-39 was found to be 0.47 mSv. For CTA, the tracks have been revealed by electrochemical etching (ECE) only and the minimum detection limit was found to be 0.85 mSv at optimum experimental parameters.

Photo-induced Hall Effect in graphene — effect of boundary types

We theoretically predict, with the Keldysh Green's function combined with the Floquet method, that the AC electric field of a circularly polarized light should induce a Hall effect, in the absence of uniform magnetic fields, in graphene with a pair of Dirac dispersions. Although the Hall coefficient is not quantized, the dynamical gap generated by the AC field and the associated Hall effect bear a topological origin which can be traced back to the Dirac cones. We also study the dependence on boundary conditions. The required AC field strength is estimated to be realistic.