Applied Field Strength Research Articles

Structural, magnetic, magnetocaloric and specific heat investigations on Mn doped PrCrO3 orthochromites

We have synthesized PrCr0.85Mn0.15O3 (PCMO) chromite and investigated the influence of manganese (Mn) doping at Cr-sites on the structural, magnetic, magnetocaloric and thermal properties of PrCrO3 compound. No structural transition was observed with Mn substitution and the doped compound crystallized into distorted orthorhombic structure with Pnma space group which was confirmed by Rietveld refinement of x-ray powder diffraction patterns. Neel temperature, noticed at 168 K from the temperature variation of magnetization, smaller than that reported for PrCrO3, indicated the influence of Mn3+ substitution in decreasing the antiferromagnetic ordering. Magnetization was almost eight times higher than that reported for undoped sample. Magnetocaloric effect measured via the magnetic entropy change and relative cooling power demonstrated significant values in the temperature range 10–20 K. The values of magnetic entropy change are much superior to that reported for other polycrystalline orthochromites and even at smaller applied field strength. The material exhibited second order magnetic phase transition. The Debye temperature and the density of states at Fermi level were also calculated. The overall results make PrCr0.85Mn0.15O3 chromite a potential candidate to replace the existing materials for low temperature magnetic refrigeration.

Effect of dipole moments on orientation and alignment of a bounded molecule

A diatomic molecule modeled by Shifted Deng-Fan (SDF) oscillator potential and restricted to a small region of space has been considered. Energy spectra and radial matrix elements have been calculated using an accurate nine-point finite difference method. Orientation and alignment is generally studied by taking into account only the permanent dipole moment of the molecule. However, in this work, dependence of these properties on the actual set of matrix elements has been explored. A comparative study of the two has been presented. Effect of boundary radius and applied field strength has also been studied.

Unconventional electroabsorption in monolayer MoS2

Signal modulation in optoelectronics is obtained by modulation of either the refractive index or the absorbance by an electric field. However, electromodulators have not kept up with the miniaturization of other electronic and optical components. Here we show a strong transverse electroabsorption signal in a monolayer of the 2D semiconductor MoS2. The electroabsorption spectrum is dominated by an apparent linewidth broadening of around 15% at a modulated voltage of only Vpp = 0.5 V. Contrary to known variants of the Stark effect, the broadening increases linearly with the applied field strength and arises from a linear variation of the distance between the strongly overlapping exciton and trion resonances. The achievable modulation depths exceeding 0.1 dB nm−1 bear the scope for extremely compact, ultrafast, energy-efficient electroabsorption modulators for integrated photonics, including on-chip optical communication.

Wasp waisted-like hysteresis loops observed in the γ-Fe2MnGa compound

Bulk and local magnetic properties of the polycrystalline Fe2MnGa compound, submitted to cold-work and annealing, have been studied using DC magnetization measurements and 57Fe Mössbauer spectroscopy in a broad temperature range (15–400 K). Structural characterization has shown stabilization of an ordered L12-type structure for annealed materials. Mechanical cold-work induces grain refinement and internal stress enhancement in the L12-type structure, favoring antisite disorder. The chemical disorder favors competitions between antiferro and ferromagnetic interactions and, consequently, leading to a frustrated magnetic state when Fe and Mn sublattices ordered magnetically. Due to the chemical disorder intrinsically found in as-prepared sample or enhanced in annealed cold-work materials, we have shown (i) metamagnetic transition from antiparallel Fe and Mn coupling to a non-collinear magnetic state when applied field strength is increased and (ii) a wasp-waisted magnetic loop character (measured in annealed materials) as consequence of frustration in magnetic interactions between misplaced Fe and Mn neighbors. We also demonstrated that even under similar experimental annealing conditions, the chemical disorders in as-prepared, ribbon and powder samples of the same batch are different, producing distinct magnetic properties of the final product.

On the role of magnetising frequency and magnetic field intensity on hysteresis loop characteristics

The goal of present research work is to study the variation in the shape of hysteresis loop owing to change in the analysis parameter i.e., magnetising frequency and applied magnetic field strength upon pack carburised low carbon steel samples. Pack carburised heat treatment performed at three different temperatures to induce varying hardness into steel samples. Hysteresis loop characteristics such as coercivity, permeability, power loss and remanence were measured in a wide range of magnetising frequency and magnetic field intensity. Coercivity is observed to increase with increase in magnetising frequency and applied field strength. In low-frequency range ( 1 Hz) results into increase in remanence and power loss. However, with an increase in magnetic field strength both remanence and power loss were found to increase.

Influence of geometry and material of insulating posts on particle trapping using positive dielectrophoresis

Insulator-based dielectrophoresis (iDEP) is a powerful particle analysis technique based on electric field scattering at material boundaries which can be used, for example, for particle filtration or to achieve chromatographic separation. Typical devices consist of microchannels containing an array of posts but large scale application was also successfully tested. Distribution and magnitude of the generated field gradients and thus the possibility to trap particles depends apart from the applied field strength on the material combination between post and surrounding medium and on the boundary shape.In this study we simulate trajectories of singe particles under the influence of positive DEP that are flowing past one single post due to an external fluid flow. We analyze the influence of key parameters (excitatory field strength, fluid flow velocity, particle size, distance from the post, post size, and cross-sectional geometry) on two benchmark criteria, i.e., a critical initial distance from the post so that trapping still occurs (at fixed particle size) and a critical minimum particle size necessary for trapping (at fixed initial distance). Our approach is fundamental and not based on finding an optimal geometry of insulating structures but rather aims to understand the underlying phenomena of particle trapping.A sensitivity analysis reveals that electric field strength and particle size have the same impact, as have fluid flow velocity and post dimension. Compared to these parameters the geometry of the post's cross-section (i.e. rhomboidal or elliptical with varying width-to-height or aspect ratio) has a rather small influence but can be used to optimize the trapping efficiency at a specific distance. We hence found an ideal aspect ratio for trapping for each base geometry and initial distance to the tip which is independent of the other parameters.As a result we present design criteria which we believe to be a valuable addition to the existing literature.

Energy coupled to matter for magnetic alignment of rare earth–doped alumina

ABSTRACTEnergy coupled to matter (ECM) concepts such as magnetic field–assisted processing were used to align rare earth–doped alumina ceramics in the presence of applied fields. The addition of gadolinium and ytterbium dopants to alumina increased the magnetic susceptibility anisotropies, and induced magnetic torques that led to significant alignment of ceramic particles under the application of magnetic fields as low as 1.8 T. In comparison, undoped alumina materials showed minimal alignment under applied field strengths as high as 9 T. Density function theory modeling indicated that the specific dopant type dictated changes in the magnetic properties of different rare earth–doped alumina systems by directly affecting the magnetic moment localization and magnetocrystalline anisotropy.

Electroporation Parameters for Successful Transdermal Delivery of Insulin.

This work investigates the effects of electroporation parameters on the transdermal delivery of insulin. Electroporation (EP) is known to induce temporal pores in the membrane, which are expected to enhance the diffusion of insulin through rabbits' skin. For such purpose, 5 different formulations of insulin and enhancers are applied to rabbit groups (5 rabbits each) with induced hyperglycemia in the presence of electroporative pulses. The blood sugar level (BSL) is followed up to 5-hour duration starting from the administration of the hyperglycemia-inducing factor. The effect of different electroporation parameters on BSL of rabbits is examined and compared with control groups. Results show that the increase in the number of pulses (from 15 up to 60 successive pulses) at an insulin concentration of 50 IU/mL, the increase in insulin concentration (from 50 to 70 IU/mL), and the decrease in applied field strength (from 200 to 100 V/cm) result in a significant decrease in BSL compared with control. Among all of the investigated formulations, the best performance is recorded for the insulin solution + EP (without enhancers) in almost all of the studied experimental conditions.

Anharmonic Bloch oscillations of electrons in electrically biased superlattices

The phenomenon of anharmonic Bloch oscillations (i.e., oscillations with a frequency which is a multiple of the Bloch frequency) is considered. The energy-band structure of silicon-carbide polytypes where these oscillations are observed is calculated ab initio. A one-dimensional model potential making it possible to calculate the Stark wave functions in a biased superlattice is constructed for these polytypes. The transfer matrix method is used to find the set of energy levels (the so-called Stark ladder) and calculate the electron wave functions. It is shown that both radiative transitions between neighboring Stark levels (at the Bloch frequency) and transitions in the form of jumps via several levels, accompanied by emission at frequencies that are multiples of the Bloch frequency, may occur. The calculated probabilities of transitions between Stark-ladder levels increase with increasing applied field strength.

Path length tunable light-matter interaction in magnetic nanofluid based field-induced photonic crystal-glass structure

The ability to control the light–matter interaction and the simultaneous tuning of both the structural order and disorder in materials, although important in photonics, remain major challenges. In this paper, we demonstrate that path length dictates light–matter interaction for the same crystal structure, formed by the ordering of magnetic nanoparticle self-assembled columns inside magnetic nanofluid under applied field. When the path length is shorter the condition for maintaining temporal coherence for the constructive interference is therefore satisfied, resulting in the formation of a concentric diffraction ring pattern; while for a longer path length only a corona ring of scattered light is observed. Analysis of diffraction ring pattern suggests the formation of 3D hexagonal crystal structure, where the longitudinal and lateral inter-column spacings are 5.281 μm and 7.344 μm, respectively. Observation of speckles and diffuse scattering background within the diffraction ring pattern confirms the presence of certain degree of crystal disorder, which can be tuned by controlling the applied field strength, nanoparticle size and particle volume fraction. Our results provide a new approach to develop next generation of tunable photonic devices, e.g. tunable random laser, based on simultaneous harnessing of the properties of disordered photonic glass and 3D photonic crystal.

Impact of in Vivo High-Field-Strength and Ultra-High-Field-Strength MR Imaging on DNA Double-Strand-Break Formation in Human Lymphocytes.

Purpose To determine the impact of different magnetic field strengths (1, 1.5, 3, and 7 T) and the effect of contrast agent on DNA double-strand-break (DSB) formation in patients undergoing magnetic resonance (MR) imaging. Materials and Methods This in vivo study was approved by the local ethics committee, and written informed consent was obtained from each patient. To analyze the level of DNA DSBs, peripheral blood mononuclear cells were isolated from blood samples drawn directly before, as well as 5 minutes and 30 minutes after MR imaging examination. After performing γH2AX immunofluorescence staining, DSBs were quantified with automated digital microscopy. MR group consisted of 43 patients (22 women, 21 men; mean age, 46.1 years; range, 20-77 years) and was further subdivided according to the applied field strength and administration of contrast agent. Additionally, 10 patients undergoing either unenhanced or contrast material-enhanced computed tomography (CT) served as positive control subjects. Statistical analysis was performed with Friedman test. Results Whereas DSBs in lymphocytes increased after CT exposure (before MR imaging: 0.14 foci per cell ± 0.05; 5 minutes after: 0.26 foci per cell ± 0.07; 30 minutes after: 0.24 foci per cell ± 0.07; P ≤ .05), no alterations were observed in patients examined with MR imaging (before MR imaging: 0.13 foci per cell ± 0.02; 5 minutes after: 0.12 foci per cell ± 0.02; 30 minutes after: 0.11 foci per cell ± 0.02; P > .05). Differentiated analysis of MR imaging subgroups again revealed no significant changes in γH2AX level. Conclusion Analysis of γH2AX foci showed no evidence of DSB induction after MR examination, independent of the applied field strength and administration of gadolinium-based contrast agent.

Theoretical Study of the Charge-Transfer State Separation within Marcus Theory: The C60-Anthracene Case Study

We study, within Marcus theory, the possibility of the charge-transfer (CT) state splitting at organic interfaces and a subsequent transport of the free charge carriers to the electrodes. As a case study we analyze model anthracene-C60 interfaces. Kinetic Monte Carlo (KMC) simulations on the cold CT state were performed at a range of applied electric fields, and with the fields applied at a range of angles to the interface to simulate the action of the electric field in a bulk heterojunction (BHJ) interface. The results show that the inclusion of polarization in our model increases CT state dissociation and charge collection. The effect of the electric field on CT state splitting and free charge carrier conduction is analyzed in detail with and without polarization. Also, depending on the relative orientation of the anthracene and C60 molecules at the interface, CT state splitting shows different behavior with respect to both applied field strength and applied field angle. The importance of the hot CT in helping the charge carrier dissociation is also analyzed in our scheme.

Tuning the caloric response of BaTiO3 by tensile epitaxial strain

We investigate the effect of epitaxial strain on the electrocaloric effect (ECE) in BaTiO3 by means of ab-initio–based molecular-dynamics simulations. We show that tensile strain can be used to optimize the operation range for ferroic cooling. Strain in the range of ≤ 1% can be used to shift the operation temperature by several hundreds of kelvin both to higher and lower temperatures, depending on the direction of the external field. In addition, the transformation between multi-domain and mono-domain states, induced by an in-plane electric field, results in an additional peak of the adiabatic temperature change at lower temperatures, and a broad temperature interval where the caloric response scales linearly with the applied field strength, even up to very high fields.

Thickness and Stacking Dependent Polarizability and Dielectric Constant of Graphene–Hexagonal Boron Nitride Composite Stacks

The giant carrier mobility of graphene is significantly reduced due to external perturbations, such as substrate based charge impurities, and their impact can be minimized by encapsulating graphene between hexagonal boron nitride (hBN) layers. Using density functional theory (DFT) based ab initio calculations, we study the static response of such a composite by placing it in a vertical electric field. We find that at relatively low electric field (∼0.1 V/A), although the relative permittivity (er) of a composite stack increases with the number of layers, er for a fixed stack thickness is independent of the field strength. However, at higher electric field strength, er increases monotonically with the applied field strength even for a fixed stack thickness, signifying nonlinear response. The relative permittivity changes more readily for graphene rich stacks as compared to hBN rich stacks, which is consistent with the property of the pristine phases. We also present an empirical formulation to calculate th...

Determining the time-dependent effective relaxation time of biofunctionalized magnetic nanoparticles conjugated with biotargets by using a high-Tc SQUID-based ac susceptometer for a magnetic immunoassay

In this study, we determined the time-dependent effective relaxation time (τeff) of biofunctionalized magnetic nanoparticles (BMNs) that were conjugated with biotargets for magnetic immunoassays. The BMNs were anti-alphafetoprotein (AFP)-coated onto dextran-coated magnetic nanoparticles to yield Fe3O4–anti-AFP. The biotarget was AFP. The time-dependent phase delay θ(t) of magnetization relative to the applied field strength was determined using a homemade high-Tc superconducting quantum interference device-based ac susceptometer. The detected θ(t) was then analyzed to derive τeff(t), the results of which showed that τeff(t) increased over time. Additionally, the change in τeff after the BMNs conjugated with the AFP (Δτeff) increased with the AFP concentration (ΦAFP). We attribute this to the additional magnetization generated when the BMNs conjugated with the AFP, which thereby reduced the Néel and Brownian relaxations and consequently improved the τeff. We established the relationship between ΔτAFP and ΦAFP and thus provide a foundation for assaying unknown quantities of AFP.

Correlation Between the Field-Driven Microscopic Magnetization Reversal and the Disorders in Ferromagnetic Systems

Understanding the field-driven microscopic magnetization reversal in a disordered ferromagnetic (FM) film is a fundamentally intriguing issue for the application of a disorder-induced magnetic memory. We present the field dependence of the correlation between local coercivity and switching time in the FM films showing two typical reversal processes: wall-motion and nucleation dominant ones. As the applied field strength increases, the correlation coefficient in the wall-motion sample decreases, whereas the one in the nucleation sample holds nearly zero value. The change in the wall-motion sample is well explained by the transition of the magnetization reversal mechanism from a thermal activation reversal to a viscous motion. This paper shows that the magnetization reversal mechanism depending on the time scale as well as the materials has a strong influence on the correlation.

Ferrofluids containing Fe3O4 nanoparticles in solidified photoresist carrier

Ferrofluids, formed by magnetic nanoparticles uniformly dispersed in a liquid carrier, respond to an external magnetic field, which enable the fluid’s position by applying a magnetic field. Here, ferrofluids composed of Fe3O4 nanoparticles with oleic acid and oleylamine as the surfactant and photoresist, respectively, were prepared. Under an external magnetic field, the movement and the position of ferrofluids and the injection of the fluids into complex shapes were easily achieved. The ferrofluid surfaces were distorted under the magnetic field, and the surface structue was controlled by the applied field strength. Using a photoresist as the liquid carrier, it was possible to solidify the ferrofluids by UV irradiation. The shape and the position of the solid superparamagnetic nanoparticles/polymer composites were also determined by the external magnetic field.

Influence of Electrolyte Concentration on the Aggregation of Colloidal Particles near Electrodes in Oscillatory Fields.

Micron-scale particles suspended in various aqueous electrolytes have been widely observed to aggregate near electrodes in response to oscillatory electric fields, a phenomenon believed to result from electrically induced flows around the particles. Previous work has focused on elucidating the effects of the applied field strength, frequency, and electrolyte type on the aggregation rate of particles, with less attention paid to the ionic strength. Here we demonstrate that an applied field causes micron-scale particles in aqueous NaCl to rapidly aggregate over a wide range of ionic strengths, but with significant differences in aggregation morphology. Optical microscopy observations reveal that at higher ionic strengths (∼1 mM) particles arrange as hexagonally closed-packed (HCP) crystals, but at lower ionic strengths (∼0.05 mM) the particles arrange in randomly closed-packed (RCP) structures. We interpret this behavior in terms of two complementary effects: an increased particle diffusivity at lower ionic strengths due to increased particle height over the electrode and the existence of a deep secondary minimum in the particle pair interaction potential at higher ionic strength that traps particles in close proximity to one another. The results suggest that electrically induced crystallization will readily occur only over a narrow range of ionic strengths.

Synthesis and properties of 1D Sm-doped CeO2 composite nanofibers fabricated using a coupled electrospinning and sol–gel methodology

Ce1−xSmxO2(x=0, 0.2, 0.5 and 0.8) nanofibers (NFs) were synthesized by coupling sol–gel with electrospinning and using poly-vinyl pyrrolidone (PVP) as the polymer medium, in an ethanol/water mixture. Control over the fabrication conditions was achieved through analysis of the most key synthetic factors, which include: (i) the applied field strength; (ii) the solution feed rate and (iii) the PVP content in the electrospinning solution. The optimum microstructural fiber morphology (high quality beeds-free fibers) was achieved using the following electrospinning parameters: an applied voltage of 18.5kV, a 7ml/h of solution feed rate and a 12% (w/w) of PVP composition. Morphological features of the resulting fibers were examined by scanning electron microscopy (SEM). The average fiber diameter was typically found to be in the range of 200–1100nm and 50–300nm, before and after calcination at 500°C, respectively. X-ray diffraction (XRD) results showed that the fluorite cubic structure was preserved for the entire Ce1−xSmxO2 compositional range studied, while elemental analysis using EELS and X-ray photoelectron spectroscopy (XPS) confirmed the purity of the bulk and surface composition of the fibers. Selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM) proved that the NFs are highly crystalline. The thermal stability of the composite (polymer/inorganic nitrate salts) NFs was further investigated in an inert atmosphere (N2) using thermogravimetric analysis (TGA), which allowed the transformation process of the NFs from composite to oxide to be monitored. The reducibility of the metal oxide NFs (mobility of oxygen species in the fluorite cubic lattice) as well as their thermal stability in successive oxidation–reduction cycles was evaluated using temperature-programmed reduction in a H2 atmosphere (H2-TPR). Acidic–basic features of the NFs and powder surfaces were studied through temperature programmed desorption (TPD) using NH3 and CO2 as probe molecules, where weak, medium and strong acid sites were successfully traced with profound differences depending on the morphology. The NFs' potential performance towards NH3 oxidation was also evaluated. Two types of basic sites, hydroxyl groups and surface lattice oxygen are present on the NFs, as probed by CO2 adsorption. Pyridine adsorption followed by infrared spectroscopy (Py-FT-IR) studies unveiled the more profound Lewis acid presence in Ce0.5Sm0.5O2 NFs compared to bulk powder Ce0.5Sm0.5O2.

C. elegans Demonstrates Distinct Behaviors within a Fixed and Uniform Electric Field.

C. elegans will orient and travel in a straight uninterrupted path directly towards the negative pole of a DC electric field. We have sought to understand the strategy worms use to navigate to the negative pole in a uniform electric field that is fixed in both direction and magnitude. We examined this behavior by quantifying three aspects of electrotaxis behavior in response to different applied field strengths: the mean approach trajectory angles of the animals’ tracks, turning behavior (pirouettes) and average population speeds. We determined that C. elegans align directly to the negative pole of an electric field at sub-preferred field strength and alter approach trajectories at higher field strengths to maintain taxis within a preferred range we have calculated to be ~ 5V/cm. We sought to identify the sensory neurons responsible for the animals’ tracking to a preferred field strength. eat-4 mutant animals defective in glutamatergic signaling of the amphid sensory neurons are severely electrotaxis defective and ceh-36 mutant animals, which are defective in the terminal differentiation of two types of sensory neurons, AWC and ASE, are partially defective in electrotaxis. To further elucidate the role of the AWC neurons, we examined the role of each of the pair of AWC neurons (AWCOFF and AWCON), which are functionally asymmetric and express different genes. nsy-5/inx-19 mutant animals, which express both neurons as AWCOFF, are severely impaired in electrotaxis behavior while nsy-1 mutants, which express both neurons as AWCON, are able to differentiate field strengths required for navigation to a specific field strength within an electric field. We also tested a strain with targeted genetic ablation of AWC neurons and found that these animals showed only slight disruption of directionality and turning behavior. These results suggest a role for AWC neurons in which complete loss of function is less disruptive than loss of functional asymmetry in electrotaxis behavior within a uniform fixed field.