Nonmagnetic Medium Research Articles

ChemInform Abstract: Polymer‐Coated Magnetic Carbonyl Iron Microparticles and Their Magnetorheological Characteristics

AbstractReview: 49 refs.

Wave coupling theory of quadratic electro-optic effect and its applications

Wave coupling theory of quadratic electro-optic effect is developed by considering the third-order nonlinearity as a perturbation in lossless nonmagnetic centrosymmetric medium. A general solution of the resultant equations is given to describe the quadratic electro-optic effect for the electromagnetic wave propagating along an arbitrary direction with applied external electric field. The effect of the polarization state on electro-optic coupling is studied in paraelectric phase KLTN crystals. A novel application of wave coupling theory of quadratic effect is described, namely polarization rotator, which can rotate the polarization of the electromagnetic wave with an arbitrary angle.

Interfacial spin polarization and resistance in lateral spin-valves incorporating Bi and BiPb thin films

Electrical spin injection and detection have been investigated at cryogenic temperatures using a lateral spin-valve structure. Either Bi or BiPb was used as a nonmagnetic spin medium, while CoFe and NiFe were employed as the spin injector and spin detector, respectively. A large magnetoresistance signal corresponding to ΔR=1.2 mΩ was detected from the BiPb-based spin-valves. From this result, a large spin diffusion length of 230 μm and a high interfacial spin polarization of 10% were derived. From an independent calculation, it was found that the interfacial spin polarization and the associated spin accumulation are strongly correlated with the interfacial resistance.

Reply to “Comment on ‘Poynting vector, heating rate, and stored energy in structured materials: A first-principles derivation’ ”

I argue that the form of the macroscopic Poynting vector derived in my paper [M. G. Silveirinha, Phys. Rev. B 80, 235120 (2009)] is self-consistent with the usual form of the microscopic Poynting vector in nonmagnetic media, and that therefore there is no arbitrariness in the definition of the macroscopic Poynting vector as long as the usual expression for the microscopic Poynting vector is accepted as valid. I also emphasize that the macroscopic Poynting vector derived in my paper is coincident with the most general form of the Poynting vector reported in the literature for reciprocal stationary spatially dispersive media.

Electromagnetic energy within magnetic spheres

Consider that an incident plane wave is scattered by a homogeneous and isotropic magnetic sphere of finite radius. We determine, by means of the rigorous Mie theory, an exact expression for the time-averaged electromagnetic energy within this particle. For magnetic scatterers, we find that the value of the average internal energy in the resonance picks is much larger than the one associated with a scatterer with the same nonmagnetic medium properties. This result is valid even, and especially, for low size parameter values. Expressions for the contributions of the radial and angular field components to the internal energy are determined. For the analytical study of the weak absorption regime, we derive an exact expression for the absorption cross section in terms of the magnetic Mie internal coefficients. We stress that, although the electromagnetic scattering by particles is a well-documented topic, almost no attention has been devoted to magnetic scatterers. Our aim is to provide some new analytical results, which can be used for magnetic particles, and emphasize the unusual properties of the magnetic scatters, which could be important in some applications.

Polymer-coated magnetic carbonyl iron microparticles and their magnetorheological characteristics

We review core/shell structured magnetic carbonyl iron (CI)/polymer hybrid particles fabricated with various polymeric systems and their magnetorheological (MR) characteristics when dispersed in non-magnetic suspending medium. Their morphology and magnetization properties are compared with those from different fabrication methodologies. Rheological characteristics of the MR fluids, exhibiting improved dispersion stability compared to the pure CI based MR fluid, are presented along with their potential engineering applications.

Boundary Eigenvalue Problem for Maxwell Equations in a Nonlinear Dielectric Layer

The propagation of TM-polarized electromagnetic waves in a dielectric layer filled with lossless, nonmagnetic, and isotropic medium is considered. The permittivity in the layer defines by Kerr law. We look for eigenvalues of the problem and reduce the issue to the analysis of the corresponding dispersion equation. The equivalence of the boundary eigenvalue problem and the dispersion equation is proved. We show that the solution of the problem exists and from dispersion equation it can be numerically obtained. Using this solution the components of electromagnetic field in the layer can be numerically obtained as well. Transition to the limit in the case of a linear medium in the layer is proved. Some numerical results are presented also.

Polariton spectrum of a bounded antiferromagnet with a center of antisymmetry in an external electric field oriented normally to the surface

The features of transmission of TE and TM polaritons through an interface between magnetic and nonmagnetic media and their localization at the interface in an external dc electric field have been studied. This field is directed along the hard magnetization axis. The magnetic medium is an easy-plane tetragonal antiferromagnet; it is odd with respect to inversion. A magnetic plate and a 1D magnetic photonic crystal in an external dc electric field, oriented normally to the interface, are considered.

Dynamics of a charged particle in progressive plane waves propagating in vacuum or plasma: Stochastic acceleration

AbstractThe dynamics of a charged particle in a relativistic strong electromagnetic plane wave propagating in a nonmagnetized medium is studied first. The problem is shown to be integrable when the wave propagates in vacuum. When it propagates in plasma, and when the full plasma response is considered, an exhaustive numerical work allows us to conclude that the problem is not integrable. The dynamics of a charged particle in a relativistic strong electromagnetic plane wave propagating along a constant homogeneous magnetic field is studied next. The problem is integrable when the wave propagates in vacuum. When it propagates in plasma, the problem becomes nonintegrable. Finally, one particle in a high intensity wave, propagating in a nonmagnetized medium, perturbed by a low intensity traveling wave is considered. Resonances are identified and conditions for resonance overlap are studied. Stochastic acceleration is shown by considering a single particle. It is confirmed in plasma in realistic situations with particle-in-cell code simulations.

Comparison of the thin flux tube approximation with 3D MHD simulations

The structure and dynamics of small vertical photospheric magnetic flux concentrations has been often treated in the framework of an approximation based upon a low-order truncation of the Taylor expansions of all quantities in the horizontal direction, together with the assumption of instantaneous total pressure balance at the boundary to the non-magnetic external medium. Formally, such an approximation is justified if the diameter of the structure (a flux tube or a flux sheet) is small compared to all other relevant length scales (scale height, radius of curvature, wavelength, etc.). The advent of realistic 3D radiative MHD simulations opens the possibility of checking the consistency of the approximation with the properties of the flux concentrations that form in the course of a simulation. We carry out a comparative analysis between the thin flux tube/sheet models and flux concentrations formed in a 3D radiation-MHD simulation. We compare the distribution of the vertical and horizontal components of the magnetic field in a 3D MHD simulation with the field distribution in the case of the thin flux tube/sheet approximation. We also consider the total (gas plus magnetic) pressure in the MHD simulation box. Flux concentrations with super-equipartition fields are reasonably well reproduced by the second-order thin flux tube/sheet approximation. The differences between approximation and simulation are due to the asymmetry and the dynamics of the simulated structures.

Atom transfer radical polymerized PMMA/magnetite nanocomposites and their magnetorheology

We synthesized core/shell-typed magnetic nanoparticle composites using poly(methyl methacrylate) (PMMA) as a shell and magnetite nanoparticle (MN) as a core, in which the PMMA shell was prepared via atomic transfer radical polymerization (ATRP) method. Chemical structure and morphology of the synthesized MN–PMMA nanocomposite were investigated using FT-IR and TEM, respectively. Magnetorheological (MR) fluid was prepared by dispersing synthesized MN–PMMA in non-magnetic medium. Both shear stress and shear viscosity of the MR fluids as a function of shear rate were measured using a rotational rheometer with a magnetic field generator, exhibiting that a yield stress increased with an external magnetic field strength.

Preparation and characterization of MR fluid consisting of magnetite particle coated with PMMA

To improve physical characteristics of MR fluid, we synthesize magnetite nanoparticles (MNP) in shape of magnetic core- poly(methyl methacrylate) (PMMA) polymeric shell by atomic transfer radical polymerization. Prepared MNPs-PMMA which possesses a density lower than that of pure MNPs were characterized by FT-IR, XPS and TEM. Synthesized MNP-PMMA based MR fluid which was dispersed in non-magnetic medium lubricant oil (Yu-base 8) with 10 vol% was prepared. Rheological properties such as shear viscosity, shear stress and storage modulus were measured by both static and dynamic tests using a rotational rheometer with various external magnetic field strength applied.

Wave heating of the solar chromosphere

The nonmagnetic interior of supergranulation cells has been thought since the 1940s to be heated by the dissipation of acoustic waves. But all attempts to measure the acoustic flux have failed to show sufficient energy for chromospheric heating. Recent space observations with TRACE, for example, have found 10% or less of the necessary flux. To explain the missing energy it has been speculated that the nonmagnetic chromosphere is heated mainly by waves related to the magnetic field. If that were correct, the whole chromosphere, magnetic as well as nonmagnetic, would be heated mainly by waves related to the magnetic field. But contrary to expectation, the radiation emerging from the nonmagnetic chromosphere shows none of the signatures of magnetic waves, only those of acoustic waves. Nearly all the heating of the nonmagnetic chromosphere must therefore be due to acoustic waves. In the magnetic network on the boundary of supergranulation cells, on the other hand, the small filling factor of the magnetic field in the photosphere implies that only a small fraction of the wave flux that travels upward to heat the chromosphere can be channeled by the magnetic field. Hence, while some of the energy that is dissipated in the magnetic network is in the form of magnetic waves, most of it must be in the form of acoustic waves. Thus, the quiet solar chromosphere, instead of being heated mainly by magnetic waves throughout, must be heated mainly by acoustic waves throughout. The full wave flux heating the quiet chromosphere must travel through the photosphere. In the nonmagnetic medium, this flux is essentially all in the form of acoustic waves; TRACE registers at most 10% of it, perhaps because of limited spatial resolution.

SH-wave propagation and localization anomalies in semi-infinite 1D magnetic phononic crystal

At the present, the composite magnetic materials with a superstructure (magnetic photonic crystals) are actively investigated in view of conditions of electromagnetic wave transmission. Some of these materials are acoustically continuous media and, then, can be considered as magnetic phononic crystals (MPC). However, the dynamic acoustic peculiarities of such structures have been disregarded. Theoretical investigation of SH-wave propagation in the gyrotropic and nongyrotropic semi-infinite one dimensional magnetic phononic crystals (1D MPC) is presented here. We have taken into account magnetoelastic interaction and the commensurability a wavelength and 1D MPC period. The transfer matrix method allowed us to determine the specific features of volume SH-wave localization and propagation near the rigid interface of 1D MPC and nonmagnetic medium. In particular, the necessary conditions of existence and dispersion relations for three types of shear surface acoustic waves localized near the external surface of 1D MPC have been found. This type of elastic excitation are exists also for a case when elastic properties of MPC components are identical. The conditions of reflectionless transmission of volume SH-waves through a finite 1D MPC have been determined.

Polariton dynamics of a bounded weak ferromagnetic in an external DC electric field normal to the interface

With a bounded easy-plane weakly ferromagnetic crystal magnetized tangentially to its surface taken as an example, it is shown that the external DC electric field (collinear simultaneously both with the easy magnetic axis and with the normal to the interface) can lead to the formation of multiple anomalies due to the quadratic magnetooptical interaction under the conditions of propagation of a volume TM or TE wave through the interface between magnetic and nonmagnetic media.

Effects of structural transformations in magnetic emulsions

Structural transformations and relevant changes in the magnetic and optical properties of magnetosensitive emulsions based on magnetic fluids are experimentally studied. Peculiarities of the changes in the magnetic susceptibility of emulsions associated with the deformation of their microdroplets and the effect of phase inversion (the transformation of dispersions of magnetic droplets in nonmagnetic media into dispersions of nonmagnetic droplets in magnetic fluids) are established. Optical effects occurring in magnetic emulsions under the combined action of a shear flow and a magnetic field are studied. It is concluded that optically active composition media may be developed on the basis of magnetic fluids.

On the refractive index for a nonmagnetic two-component medium: Resolution of a controversy

The refractive index of a dielectric medium comprising both passive and inverted components in its permittivity was determined using two methods: (i) in the time-domain, a finite-difference algorithm to compute the frequency-domain reflectance from reflection data for a pulsed plane wave that is normally incident on a dielectric half-space and (ii) in the frequency-domain, the deflection of an obliquely incident Gaussian beam on transmission through a dielectric slab. The dielectric medium was found to be an active medium with a negative real part for its refractive index. Thereby, a recent controversy in the scientific literature was resolved.

New mechanism of the schoch effect in nonmagnetic dielectrics

A new type of a linear relation between the components of the magnetic field vector and those of the elastic strain tensor (a dynamic piezomagnetic interaction) is proposed. This relation is irrespective of the crystal symmetry and of the presence of a magnetic structure in the dielectric medium. This leads to anomalies in the reflection of a beam of shear bulk waves incident from the depth of the nonmagnetic dielectric medium on either its mechanically free surface or its slip boundary with a semibounded magnetic medium.

Localization of a transverse elastic wave in a semibounded acoustic superlattice of ferrimagnetic and superconducting layers: 3. Leaky surface modes and associated resonances

In terms of the effective medium method, conditions for the existence of leaky shear surface acoustic waves in a semibounded fine-layered magnetic superlattice consisting of ferrimagnetic and superconducting layers are determined. On this basis, the possibility of a resonance interaction between a surface elastic SH wave propagating in the magnetic superlattice and a shear bulk wave propagating in the adjacent nonmagnetic medium is investigated.

Modeling and simulation of surface roughness in magnetorheological abrasive flow finishing (MRAFF) process

Magnetorheological abrasive flow finishing (MRAFF) process was developed for super finishing of internal geometries of hard materials. This process relies for its performance on magnetorheological effect exhibited by carbonyl iron particles along with abrasive particles in non-magnetic viscoplastic base medium. The extent of finishing action depends on radial and tangential forces coming on abrasive particles due to carbonyl iron particles (CIPs) arranged in columnar structure in the presence of external magnetic field. Experiments were conducted on stainless steel work pieces with different combinations of CIP and SiC particles in MRP-fluid for same volume concentration. CIP chain structure and surface roughness evaluation model have been proposed. Magnitudes of the forces on abrasive particles were then calculated and change in surface roughness was computed using the model developed to simulate final surface roughness.