Electromagnetic Spin Research Articles

Spatial dynamics of hybrid electromagnetic spin waves in a lateral multiferroic microwaveguide

Regimes of the formation of spatial structures at the propagation of hybrid electromagnetic spin waves in a system of laterally coupled multiferroics, which consist of parallel ferromagnetic microwaveguides with a ferroelectric layer, are studied experimentally and theoretically. Brillouin spectroscopy measurements at frequencies near the ferromagnetic resonance by the method of selection of mode patterns reveal a sharp increase in the spatial scales of transfer of power between microwaveguides. The calculations of the characteristics of propagation of electromagnetic spin wave in a lateral multiferroic structure with a finite width show that energy exchange between films is due to the features of intermodal coupling between waves. Higher transverse modes and electric-field-induced transformation of spectra of the electromagnetic spin waves in the adjacent multiferroics are studied experimentally and numerically.

Computational modeling of magnetohydrodynamic convection from a rotating cone in orthotropic Darcian porous media

Free convective magnetohydrodynamic flow from a spinning vertical cone to an orthotropic Darcian porous medium under a transverse magnetic field is studied. The non-dimensionalized two-point boundary value problem is solved numerically using the Keller Box implicit finite difference method. The effects of spin parameter, orthotropic permeability functions, Prandtl number and hydromagnetic number on flow characteristics are presented graphically. Tangential velocity and swirl velocity are accentuated with increasing permeability owing to a corresponding decrease in porous media resistance. Temperatures are depressed with increasing permeability. Validation of the solutions is achieved with earlier studies. Applications of the study arise in electromagnetic spin coating materials processing.

The 2015 outburst of the accreting millisecond pulsar IGR J17511–3057 as seen by INTEGRAL,Swift, andXMM-Newton

We report on INTEGRAL, Swift and XMM-Newton observations of IGR J17511-3057 performed during the outburst that occurred between March 23 and April 25, 2015. The source reached a peak flux of 0.7(2)E-9 erg/cm$^2$/s and decayed to quiescence in approximately a month. The X-ray spectrum was dominated by a power-law with photon index between 1.6 and 1.8, which we interpreted as thermal Comptonization in an electron cloud with temperature > 20 keV . A broad ({\sigma} ~ 1 keV) emission line was detected at an energy (E = 6.9$^{+0.2}_{-0.3}$ keV) compatible with the K{\alpha} transition of ionized Fe, suggesting an origin in the inner regions of the accretion disk. The outburst flux and spectral properties shown during this outburst were remarkably similar to those observed during the previous accretion event detected from the source in 2009. Coherent pulsations at the pulsar spin period were detected in the XMM-Newton and INTEGRAL data, at a frequency compatible with the value observed in 2009. Assuming that the source spun up during the 2015 outburst at the same rate observed during the previous outburst, we derive a conservative upper limit on the spin down rate during quiescence of 3.5E-15 Hz/s. Interpreting this value in terms of electromagnetic spin down yields an upper limit of 3.6E26 G/cm$^3$ to the pulsar magnetic dipole (assuming a magnetic inclination angle of 30{\deg}). We also report on the detection of five type-I X-ray bursts (three in the XMM-Newton data, two in the INTEGRAL data), none of which indicated photospheric radius expansion.

Confined states in photonic-magnonic crystals with complex unit cell

We have investigated multifunctional periodic structures in which electromagnetic waves and spin waves can be confined in the same areas. Such simultaneous localization of both sorts of excitations can potentially enhance the interaction between electromagnetic waves and spin waves. The system we considered has a form of one dimensional photonic-magnonic crystal with two types of magnetic layers (thicker and thinner ones) separated by sections of the dielectric photonic crystals. We focused on the electromagnetic defect modes localized in the magnetic layers (areas where spin waves can be excited) and decaying in the sections of conventional (nonmagnetic) photonic crystals. We showed how the change of relative thickness of two types of the magnetic layers can influence on the spectrum of spin waves and electromagnetic defect modes, both localized in magnetic parts of the system.

Tuning the bandgaps in a magnonic crystal–ferroelectric–magnonic crystal layered structure

A dispersion relation has been obtained for the hybrid electromagnetic spin wave in a magnonic crystal–ferroelectric–magnonic crystal layered structure. The mechanisms of the bandgap formation in this structure have been revealed, and the ability to double tune bandgap characteristics by means of the electric and magnetic fields has been shown.

Spin state switching of metal complexes by visible light or hard X-rays.

Electromagnetic stimuli of spin crossover compounds restricted to UV-vis light irradiation for many years could be recently extended to X-ray excitation. This review covers a large variety of light-induced effects, as well as recent analogues stimulated by X-ray irradiation which have not yet been reviewed. The focus is also on multistable multinuclear spin crossover compounds which are the subject of lively discussions within the spin crossover community. Their spin transition often occurs incompletely and with different switching mechanisms. In this review, we recall a predicted sequential switching induced thermally as well as a concerted stimulation mechanism by light irradiation for these interesting multifunctional materials.

Optical torque: Electromagnetic spin and orbital-angular-momentum conservation laws and their significance

The physics involved in the fundamental conservation equations of the spin and orbital angular momenta leads to new laws and phenomena that I disclose. To this end, I analyse the scattering of an electromagnetic wavefield by the canonical system constituted by a small particle, which I assume dipolar in the wide sense. Specifically, under quite general conditions these laws lead to understanding how is the contribution and weight of each of those angular momenta to the electromagnetic torque exerted by the field on the object, which is shown to consist of an extinction and a scattering, or recoil, part. This leads to an interpretation of its effect different to that taken up till now by many theoretical and experimental works, and implies that a part of the recoil torque cancels the usually called intrinsic torque which was often considered responsible of the particle spinning. In addition, I obtain the contribution of the spatial structure of the wave to this torque, unknown to this date, showing its effect in the orbiting of the object, and demonstrating that it often leads to a negative torque on a single particle, i.e. opposite to the incident helicity, producing an orbital motion contrary to its spinning. Furthermore, I establish a decomposition of the electromagnetic torque into conservative and non-conservative components in which the helicity and its flow play a role analogous to the energy and its flux for electromagnetic forces. I illustrate these phenomena with examples of beams, also showing the difficulties of some paraxial formulations whose fields do not hold the transversality condition.

On the transformations generated by the electromagnetic spin and orbital angular momentum operators

We present a study of the properties of the transversal "spin angular momentum" and "orbital angular momentum" operators. We show that the "spin angular momentum" operators are generators of spatial translations which depend on helicity and frequency and that the "orbital angular momentum" operators generate transformations which are a sequence of this kind of translations and rotations. We give some examples of the use of these operators in light matter interaction problems. Their relationship with the helicity operator allows to involve the electromagnetic duality symmetry in the analysis. We also find that simultaneous eigenstates of the three "spin" operators and parity define a type of standing modes which has been recently singled out for the interaction of light with chiral molecules. With respect to the relationship between "spin angular momentum", polarization, and total angular momentum, we show that, except for the case of a single plane wave, the total angular momentum of the field is decoupled from its vectorial degrees of freedom even in the regime where the paraxial approximation holds. Finally, we point out a relationship between the three "spin" operators and the spatial part of the Pauli-Lubanski four vector.

Theoretical analysis of microwave properties of ferrite-ferroelectric magnonic crystals

Microwave properties of ferrite-ferroelectric magnonic crystals are investigated for the first time. The electric and magnetic rearrangement of the band gaps in the spectrum of proper electromagnetic spin waves in such structures is demonstrated.

Electromagnetic spin–orbit interaction and giant spin-Hall effect in dielectric particle clusters

Abstract We report a phenomenon that electromagnetic spin–orbit interactions can be tailored by dielectric nanoparticles, and self-similar giant spin-Hall effect has been observed in the dielectric particle cluster. The near-field phase singularities and phase vorticity in the longitudinal component of scattered field can also be controlled by such a dielectric structure. The origin of phenomena is believed to be due to the collective resonance excitation in the dielectric particle cluster. It is expected to find applications in optics information processing and designing new nanophotonic devices.

Rashba fields in a two-dimensional electron gas at electromagnetic spin resonance

Rashba fields in a two-dimensional electron gas at electromagnetic spin resonance

Envelope solitons of electromagnetic spin waves in an artificial layered multiferroic

The nonlinear wave properties of an artificial multiferroic medium consisting of a ferroelectric layer and a ferromagnetic layer have been studied. The simultaneous effect of wave nonlinearities of both layers on the formation and propagation of envelope solitons has been analyzed. It has been shown that bright envelope solitons of electromagnetic spin waves can appear in such a medium owing to the wave nonlinearity of ferroelectric layer. In order to confirm the theoretical results, the coefficients of the nonlinear Schrodinger equation have been calculated and this equation has been solved numerically.

Hybridization of electromagnetic, spin and acoustic waves in magnetic having conical spiral ferromagnetic order

The spectrum of hybrid electromagnetic–spin–acoustic waves for magnetic having conical spiral ferromagnetic structure defined by heterogeneous exchange and relativistic interactions has been received. The possibility of resonant interaction of spin, electromagnetic and acoustic waves has been shown. The electromagnetic waves reflectance from the half-infinity layer of magnetic having conical spiral ferromagnetic order has been calculated for different values of external magnetic field (angle of spiral). The acoustic Faraday effect has been considered.

Electronic structure and Fermi surface of iron-based superconductors R2Fe3Si5 (R = Lu;Y;Sc) from first principles

Electronic structures of three superconducting rare-earth iron silicides (Lu;Y;Sc)2Fe3Si5 and non-superconducting Lu2Ru3Si5, adopting a tetragonal crystal structure (P4/mnc), have been calculated employing the full-potential local-orbital method within the density functional theory. The investigations were focused particularly on the band structures and Fermi surfaces, existing in four bands and containing rather three-dimensional electronlike and holelike sheets. They support an idea of unconventional multi-band superconductivity in these ternaries, proposed earlier by other authors for Lu2Fe3Si5, based on heat-capacity, resistivity, electromagnetic and muon spin rotation measurements. Finally, a discussion on differences in the electronic structures between the investigated here and other common families of iron-based superconductors is carried out.

Role of Different Reactive Oxygen Species in Homocysteine‐induced NALP3 Inflammasome Activation in Mouse Podocytes

Our recent studies have demonstrated the importance of NADPH oxidase‐mediated NALP3 inflammasome activation in both cultured podocytes and glomeruli of mice with hyperhomocysteinemia (hHcys). However, it remains unknown whether NADPH oxidase‐derived superoxide (O2•−) or other reactive oxygen species (ROS) are responsible for this activation. The present study tested the role of four common endogenous ROS – O2•−, hydrogen peroxide (H2O2), peroxynitrite (ONOO−), and hydroxyl radical (OH) in NALP3 inflammasome activation by using their selective scavengers or enzyme inhibitors. Confocal microscopy showed that dismutation of O2•− by 4‐hydroxy‐2,2,6,6‐tetramethyl‐piperidinyloxy (TEMPOL) markedly reduced Hcysinduced colocalization of inflammasome protein NALP3 with ASC by 60.4% and NALP3 with caspase‐1 by 64.1% in podocytes. Size exclusion chromatography also demonstrated that TEMPOL inhibited Hcys‐induced NALP3 inflammasome formation by preventing ASC recruitment to higher molecular weight fractions. Scavenging of ONOO− by uric acid also prevented Hcys‐induced aggregation of NALP3 inflammasome proteins. Furthermore, TEMPOL and uric acid treatment were able to inhibit Hcys‐induced caspase‐1 activation, respectively by 40.5% and 39.2%, as well as IL‐1β production by 46.8% and 39.4%. By electromagnetic spin resonance spectrometry, Hcys was shown to increase superoxide production by 2.2 folds compared to control podocytes, which was inhibited by 71.5% by TEMPOL and 62.2% by uric acid. However, H2O2 decomposer, catalase and hydroxyl radical scavenger, tetramethylthiourea (TMTU) had no inhibitory effects on Hcys‐induced NALP3 inflammasome protein aggregation and increases in caspase‐1 activity and IL‐1β production. These results indicate that O2•− and ONOO−, but not H2O2 or OH play an important role in mediating Hcys‐induced NALP3 inflammasome activation in podocytes (supported by NIH grants HL057244 and DK54927).

On the sensitivity of surface NMR in the presence of electrical conductivity anomalies

The surface-NMR tomography technique is based on the principles of electromagnetic induction and proton spin dynamics. Electromagnetic fields emitted by large surface current-driven loops are employed to locate and quantify groundwater reservoirs. The oscillating magnetic fields interact with proton spins of water molecules in the electrically conductive subsurface. To study the influence of changing subsurface electrical properties on the nuclear spin response, we consider the spin magnetization as a virtual magnetic dipole receiver. The numerical solutions for the electric and magnetic fields of the transmitter and the virtual receiver in 3-D heterogeneous ground are based on the finite-element method. We explicitly compute the frequency-domain electromagnetic sensitivities for separate spin magnetizations in a groundwater aquifer to study the distortion of the NMR response because of electrical heterogeneities in the medium. Analyses of entire pulse moment sequences yield the cumulative sensitivities to electrical conductivity and water-content variations in the subsurface. We illustrate the influence of conductivity on NMR responses using a limited number of models. From these models we found that electrical conductivity anomalies in the shallow subsurface (<50 m) having values =0.1 S m-1 and volumes with linear dimensions in the order of our loop size (i.e. edge length 100 m) can have a strong influence on the NMR response and ought to be taken into account in the inversion of surface-NMR data. The effect increases non-linearly with increased body size, increased conductivity contrast and decreased anomaly depth.

Scattering by an electromagnetic radiation field

Motion of test particles in the gravitational field associated with an electromagnetic plane wave is investigated. The interaction with the radiation field is modeled by a force term {\it \`a la} Poynting-Robertson entering the equations of motion given by the 4-momentum density of radiation observed in the particle's rest frame with a multiplicative constant factor expressing the strength of the interaction itself. Explicit analytical solutions are obtained. Scattering of fields by the electromagnetic wave, i.e., scalar (spin 0), massless spin $\frac12$ and electromagnetic (spin 1) fields, is studied too.

Electromagnetic spin polarization on the surface of topological insulator

We study the spin polarization of the electrons on the surface of topological insulators under a dc electric field or a circularly polarized light by using the Keldysh Green's function formalism. When a dc electric field ${E}_{x}\ensuremath{\sim}{10}^{3}\phantom{\rule{0.28em}{0ex}}\mathrm{V}/\mathrm{m}$ is applied, a spin polarization $\ensuremath{\langle}{\ensuremath{\sigma}}_{y}\ensuremath{\rangle}\ensuremath{\simeq}5.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\phantom{\rule{0.28em}{0ex}}{\AA{}}^{\ensuremath{-}2}$ is induced. Furthermore, we also find that a light illumination induces the out-of-plane component of the spin polarization as a result of the inverse Faraday effect. The magnitude of the spin polarization is proportional to the square of the lifetime $\ensuremath{\tau}$ and $\ensuremath{\langle}{\ensuremath{\sigma}}_{z}\ensuremath{\rangle}\ensuremath{\simeq}2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\phantom{\rule{0.28em}{0ex}}{\AA{}}^{\ensuremath{-}2}$ for typical parameters. Finally, we investigate the spin polarization in the presence of the warping term. By the symmetry consideration of the system, we find that the out-of-plane spin polarization is cubic of the current and that the magnitude of the induced spin polarization depends on the direction of the applied current.

NADPH Oxidase‐Mediated Activation of Inflammasomes by Increased Homocysteine in Mouse Podocytes and Glomeruli

Recent studies in our laboratory have found that activation of inflammasomes may turn on the inflammatory response to homocysteine (Hcys), leading to podocyte dysfunction and glomerular sclerosis. The present study was designed to test whether NADPH oxidase-mediated redox signaling contributes to Hcys-induced inflammasome activation in podocytes. By confocal microscopy, Hcys treatment was found to induce inflammasome formation and activation, as shown by an approximate 2.5-fold increase in colocalization between the 3 major inflammasome components - NALP3, apoptosis-associated speck-like protein (ASC), and caspase-1. Accompanying such aggregation of inflammasome components, caspase-1 activity was doubled and IL-1β production was markably increased (1.05±0.12 vs. 0.39±0.06 pg/ml of control). All of these changes in podocytes were significantly blocked by silencing the ASC gene or by inhibition of NADPH oxidase using apocynin, gp91phox peptide, and gp91phox siRNA. Using electromagnetic spin resonance spectrometry, Hcys-induced superoxide production was considerably inhibited by 60% with gp91phox siRNA. In wild type mice with hyperhomocysteinemia (hHcys) induced by folate-free diet, NALP3, ASC, and caspase-1 aggregation in the glomeruli was found at an early stage, which occurred in podocytes as shown by colocalization with podocyte marker such as podocin. In gp91phox knockout mice, however, hHcys-induced inflammasome formation and activation were not observed. These results suggest that Hcys-induced NADPH oxidase activation is importantly involved in the switching on process of NALP3 inflammasomes in podocytes (supported by NIH grants HL057244 and DK54927).

Reversal by Growth Hormone of Homocysteine-induced Epithelial-to-Mesenchymal Transition through Membrane Raft-Redox Signaling in Podocytes

Epithelial-to-Mesenchymal Transition (EMT) is an important pathogenic mechanism mediating glomerular injury or sclerosis in a variety of renal and systemic diseases such as hyperhomocysteinemia (hHcys). The present study was designed to test whether Hcys-induced EMT in podocytes is reversed by growth hormone (GH), a hormone regulating cell differentiation and growth and to explore the cellular and molecular mechanism mediating its action. It was found that Hcys induced significant EMT in podocytes, as shown by marked decreases in slit diaphragm-associated protein P-cadherin and zonula occludens-1 as epithelial markers and by dramatic increases in the expression of mesenchymal markers, fibroblast specific protein-1 and α-smooth muscle actin, which were detected by all examinations via immunocytochemistry, real time RT-PCR and Western blot analysis. When podocytes were treated with GH at 25 ng/mL, however, Hcys failed to induce podocyte EMT. Using electromagnetic spin resonance spectrometry, Hcys-induced superoxide (O₂.^-) production via NADPH oxidase was found to be significantly inhibited by GH (66%). Functionally, GH was shown to substantially inhibit Hcys-induced increases in the permeability of podocyte monolayers and to block the decrease in podocin expression in these cells. In addition, NADPH oxidase subunit, gp91^phox and GH receptors aggregated in membrane raft clusters, which produced O₂.^- in response to Hcys and could be blocked by GH, membrane raft disruptors filipin and MCD or NADPH oxidase inhibitor, apocynin. It is concluded that Hcys-induced podocyte EMT is associated with transmembrane membrane raft-redox signaling and that GH reverses this Hcys-induced EMT protecting podocytes from functional disturbance.