Structure In External Magnetic Field Research Articles

The Long Filament of PSR J2030+4415

Abstract New X-ray and optical observations shed light on the remarkable X-ray filament of the gamma-ray pulsar PSR J2030+4415. Images of the associated Hα bow shock’s evolution over the past decade compared with its velocity structure provide an improved kinematic distance of ∼0.5 kpc. These velocities also imply that the pulsar spin axis lies ∼15° from the proper motion axis, which is close to the plane of the sky. The multi-bubble shock structure indicates that the bow shock standoff was compressed to a small value ∼20–30 yr ago when the pulsar broke through the bow shock to its present bubble. This compression allowed multi-TeV pulsar e ± to escape to the external interstellar medium (ISM), lighting up an external magnetic field structure as the filament. The narrow filament indicates excellent initial confinement and the full 15′ (2.2 pc = 7 lt-yr) projected length of the filament indicates rapid e ± propagation to its end. Spectral variation along the filament suggests that the injected particle energy evolved during the breakthrough event.

Radiation from shallow oxygen impurity in AlGaN/GaN HEMT structures in magnetic field

The electrically excited impurity emission from AlGaN/GaN high electron mobility transistor (HEMT) structures in external magnetic field varying from 1.2 T to 1.5 T was investigated in this work at temperature of 4.2 K. We have observed the sharp emission line at (263 ± 1) cm−1 with FWHM of (5.8 ± 0.8) cm−1, which we have attributed to radiative electronic transitions in residual oxygen impurity atoms. The blueshift of resonant transition frequency due to presence of external magnetic field was observed. The width of the peak was found to be defined mainly by the thermal broadening at 4.2 K.

Magnetic and thermodynamic properties of a ternary metal nanoisland: A Monte Carlo study

Using the Monte Carlo simulation, the magnetic and thermodynamic properties of a ferrimagnetic mixed-spin (1, 3/2, 2) ternary metal nanoisland with core–shell structure in external magnetic field have been researched detailedly. The effects of crystal-field, exchange coupling and temperature on magnetization, susceptibility, blocking temperature and internal energy as well as hysteresis loops behavior of the system have been exhibited. Some interesting phenomena such as multiple saturation magnetizations and rich hysteresis loops behaviors have been found. The results can be comparable with some theoretical and experimental researches.

Composition- and magnetic field-driven antiferromagnetic-weak ferromagnetic transition in Bi1−xCaxFe1−xTixO3 multiferroics

The investigation aims at assessing the influence of Ca2+/Ti4+ co-doping on the crystal structure and magnetic properties of the BiFeO3 multiferroic exhibiting cycloidal spin ordering in the polar phase. We show that increasing the content of the substituents results in reducing the stability range of the cycloidal antiferromagnetic structure in external magnetic field. Above the critical concentration corresponding to the composition with x=0.15, the cycloidal order is removed to enable the formation of a weak ferromagnetic state. The spontaneous magnetization characteristic of the doping-stabilized weak ferromagnetic phase is very close to the locked magnetization releasing upon the magnetic field-induced cycloidal ordering ↔ canted ordering transition observed in the compounds with x≤0.15. Since the doping-driven magnetic transformation is not accompanied by changes in the symmetry of the crystal lattice, the Ca2+/Ti4+ co-substitution provides a promising opportunity to combine switchable magnetization and polarization in a single phase.

Proximity effect for asymmetrical three-layered F/S structures in external magnetic field

We study the critical temperature Tc of the three-layered ferromagnet/superconductor (F/S) structures in the external magnetic field H parallel to the film. For the F1/S/F2 and F1/F2/S asymmetrical trilayers, the triplet superconducting component is generated at noncollinear magnetizations of the F layers. Assuming that all S and F layers are dirty, we solve boundary problem for the Usadel function. The results of numerical calculations for Tc as function thicknesses both F1 and F2 layers at various parameters F/S structure are presented. The application to the spin-switch problem is discussed. We found that asymmetry can essentially change the spin-switch observation condition. The re-entrant superconductivity caused by external magnetic field is predicted for the F1/F2/S trilayer.

Proximity Effect for Asymmetrical Three-Layered FS Structures in External Magnetic Field

We study asymmetrical three-layers F1F2S and F1SF2 structures in an external parallelmag-netic field. Assuming that all F and S layers are dirty, we solve the boundary value problem for theUsadel function. We calculate the critical temperature of in the F1F2S and F1SF2 systems as functionof the F layers thicknesses and external magnetic field.

Magnetic Nanotubes as an Element in Biocomposites

In this work magnetic nanorods have been synthesized by electrodeposition inside the nanotubes fixed to anodic alumina oxide (AAO). The used templates have the pore diameter of 120 nm. In the first step different combinations of 3d elements oxide nanotubes such as: CoO, NiO, NiFe2O4, CoFe2O4 and Fe3O4, have been successfully fabricated inside the nanopores by wetting chemical deposition followed by thermal decomposition. Oxide/Fe, wires were obtained in the next step by electrodeposition The morphology of obtained structures were studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The magnetic properties of the nanostructures were determined on the base of behavior of the structures in external magnetic field. Local magnetic moment orientation is not strictly determined up to now. The potential biological application as an enzyme carrier was tested.

Gravitational dynamos and the low-frequency geomagnetic secular variation.

Self-sustaining numerical dynamos are used to infer the sources of low-frequency secular variation of the geomagnetic field. Gravitational dynamo models powered by compositional convection in an electrically conducting, rotating fluid shell exhibit several regimes of magnetic field behavior with an increasing Rayleigh number of the convection, including nearly steady dipoles, chaotic nonreversing dipoles, and chaotic reversing dipoles. The time average dipole strength and dipolarity of the magnetic field decrease, whereas the dipole variability, average dipole tilt angle, and frequency of polarity reversals increase with Rayleigh number. Chaotic gravitational dynamos have large-amplitude dipole secular variation with maximum power at frequencies corresponding to a few cycles per million years on Earth. Their external magnetic field structure, dipole statistics, low-frequency power spectra, and polarity reversal frequency are comparable to the geomagnetic field. The magnetic variability is driven by the Lorentz force and is characterized by an inverse correlation between dynamo magnetic and kinetic energy fluctuations. A constant energy dissipation theory accounts for this inverse energy correlation, which is shown to produce conditions favorable for dipole drift, polarity reversals, and excursions.

Changes of properties of bigyrotropic band gap structures in external magnetic field

The behaviour of reflection and transmission factors for linearly polarized irradiation passage through inhomogeneous multilayered bigyrotropic structure in external magnetic field is investigated. The changes of width, amplitude and position of the basic maximum on spectral curve of transmission factor and subordinate lobe on spectral curve of reflection factor are obtained. It is shown that the effects of basic maximum width and amplitude changes are even on the polarization sign (left- or right-hand circular), whereas the effect of basic maximum position shift on transmission factor curve is different for the signs for the indicated two polarizations.

The compressibility of bismuth and its upper transition pressure

The investigation aims at assessing the influence of Ca2+/Ti4+ co-doping on the crystal structure and magnetic properties of the BiFeO3 multiferroic exhibiting cycloidal spin ordering in the polar phase. We show that increasing the content of the substituents results in reducing the stability range of the cycloidal antiferromagnetic structure in external magnetic field. Above the critical concentration corresponding to the composition with x=0.15, the cycloidal order is removed to enable the formation of a weak ferromagnetic state. The spontaneous magnetization characteristic of the doping-stabilized weak ferromagnetic phase is very close to the locked magnetization releasing upon the magnetic field-induced cycloidal ordering ↔ canted ordering transition observed in the compounds with x≤0.15. Since the doping-driven magnetic transformation is not accompanied by changes in the symmetry of the crystal lattice, the Ca2+/Ti4+ co-substitution provides a promising opportunity to combine switchable magnetization and polarization in a single phase.