Interband absorption coefficient of the DMS cylindrical quantum wire

Using the free energy functional with two coupled order parameters the model of a rare earth ferromagnetic superconductor is considered by means of the Landau theory of phase transitions. By making the experimentally verified assumption about the dependence of critical temperatures for magnetic and superconducting subsystems on the concentration of magnetic rare earth atoms, the resulting phase diagrams are analysed in the temperature—concentration plane. It turns out that for weak coupling between magnetic and superconducting subsystems the uniform coexistence state of ferromagnetism and superconductivity sets in, while for strong coupling a spatially non‐uniform metastable state exhibiting hysteretic behaviour for ferromagnetic and superconducting phase appears. The explicit dependence of the order parameters on the temperature and concentration of magnetic atoms is also given.

In this theoretical study, we investigate optical properties of a hollow cylindrical quantum wire in the presence of a homogeneous magnetic field. The magnetic field is applied parallel to the axis of the quantum wire. The investigations were achieved by solving the Schrödinger equation within the effective mass approximation. The optical properties studied were absorption coefficient (AC) of electromagnetic radiation and changes in refractive index (CRI) of the hollow cylinder. The parallel applied magnetic field lifts the degeneracy of states of opposite angular momentum (the ±|m|\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\pm |m |$$\\end{document} states, m being the angular momentum quantum number) known as the Zeeman splitting. As such, in the presence of magnetic field, AC splits into two branches, one corresponding to a transition involving the positive m states and the other corresponding to a transition involving the negative m states. Increase in intensity of the electromagnetic radiation reduces the magnitude of the AC. Presence of inner radius of the hollow cylindrical wire lowers transition energies. Apart from absorption due to the (m=0→±1)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(m=0 \\rightarrow \\pm 1)$$\\end{document} transitions, the presence of the inner radius also facilitates absorption due the (m=-1→0)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(m=-1\\rightarrow 0)$$\\end{document} transition as the magnetic field strength increases, a phenomenon that does not happen in solid cylindrical quantum wires. The presence of the inner radius also enhances AC in strong magnetic field. Increase in intensity of the electromagnetic radiation affects the CRI (here considered up to third order), introducing a normal dispersion region in an otherwise anomalous region. The parallel magnetic field also splits the CRI depending on the sign of the m states involved in the transitions.

The mechanism of carriers accompanied by spin-wave cloud and Jahn–Teller phononic cloud, called composite polaron, is proposed to explain the unusual transport and thermodynamic properties in perovskite manganites over all the temperature and magnetic field range. It is shown that the energy bandwidth of composite polarons is strongly renormalized with the increases of temperature and magnetic field, the bandwidth narrows with elevated temperature, while it broadens with increasing magnetic field. The resistivity of composite polarons increases with elevated temperature strongly, reaches a maximum near the Curie temperature TC, and decreases with the increase of magnetic field. The specific heat of composite polarons also exhibits a maximum near TC. These results agree with experiments in a broad temperature and magnetic field range, suggesting that composite polarons contribute to the unusual properties in manganites.

The current work reports on the significant rise of the fusion triple product in experiments carried out on the compact spherical tokamak (ST) Globus-M2 with a twofold increase in the toroidal magnetic field. A tenfold rise in the n . T . τ E product was recorded during an increase in the magnetic field from 0.4 to 0.8 T and the plasma current from 0.25 to 0.4 MA at an unchanged auxiliary heating power value. Limited reasons may affect this positive trend, among which are energy confinement improvement and an increase in the efficiency of neutral beam heating. Despite the increase in the magnetic field, the neutral beam injection (NBI) led to clear and reproducible transition to the H-mode accompanied by a decrease in the turbulence level at the plasma edge. It was experimentally confirmed that strong dependence of the energy confinement time on the magnetic field value is conserved at a higher magnetic field approaching 0.8 T. Enhancement of energy confinement is connected to a collisionality (ν *) decrease. While for conventional tokamaks the confinement dependence on collisionality becomes weaker with decreasing ν * dependence, in the ST, in contrast, we observe its strengthening.

The flow of an electrically conducting incompressible viscous fluid in a plane channel with smooth expansion in the presence of a uniform transverse magnetic field has been analysed. A solution technique for the governing magnetohydrodynamic equations in primitive variable formulation has been developed. A co‐ordinate transformation has been employed to map the infinite irregular domain into a finite regular computational domain. The governing equations are discretized using finite‐difference approximations in staggered grid. Pressure Poisson equation and pressure correction formulae are derived and solved numerically. It is found that with increase in the magnetic field, the size of the flow separation zone diminishes and for sufficiently large magnetic field, the separation zone disappears completely. The peak u‐velocity decreases with increase in the magnetic field. It is also found that the asymmetric flow in a symmetric geometry, which occurs at moderate Reynolds numbers, becomes symmetric with sufficient increase in the transverse magnetic field. Thus, a transverse magnetic field of suitable strength has a stabilizing effect in controlling flow separation, as also in delaying the transition to turbulence. Copyright © 2008 John Wiley & Sons, Ltd.

In the present work, the optical properties of a GaAs cylindrical quantum dot in the presence of an applied magnetic field is studied. For this purpose, the effect of magnetic field on linear, nonlinear and total refractive index changes and absorption coefficients is investigated. According to the obtained results, it is found that: (i) The linear, nonlinear, and total refractive index changes increase and shift towards higher energies when the magnetic field increases. (ii) The linear, nonlinear, and total absorption coefficient increases when the magnetic field increases. Also, the resonance peak shifts towards higher energies by increasing magnetic field.

Magnetic and structural phase transitions in a dilute magnet with configurational degrees of freedom: II. Temperature-concentration phase diagrams

The magnetic properties of a diluted spin-2 and spin-5/2 ferrimagnetic Ising system are investigated on the basis of the effective-field theory with correlations. In particular, the effect of a positive single-ion anisotropy D on the compensation temperature in a pure system with D only on spin-5/2 atoms is investigated, in order to clarify the characteristic feature of the temperature dependence of the total magnetization M observed in a molecular-based magnetic material, . The influences of D and the concentrations of magnetic atoms on the properties of the system on a honeycomb lattice are examined. The results show that several (two or three) compensation points are possible in the diluted system with special values of D and concentrations of magnetic atoms.

Nickel (Ni) layers are commonly utilized in various applications, such as automotive components. By using a magnetic field during the electroplating process, it is possible to achieve better properties. Ni electroplating was conducted in 0.5 M nickel sulphate in this research. Various low intensities of the magnetic field (0.08 T and 0.14 T) were applied during the electroplating process. In the past, it has been demonstrated that an increase in low magnetic field could result in a decrease in crystallite size and a rise in hardness. Samples were weighed with a digital scale to determine the deposition rate and current efficiencies. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and hardness tester were performed to investigate Ni layers properties. The magnetic field influences the deposition rate, cathodic current efficiency, surface morphology, structure, and hardness properties. The increase in the magnetic field caused a wider grain and smaller crystallite sizes. The crystallite sizes of the NiS - 0, NiS - 8, and NiS - 14 samples are 33.536 nm, 33.083 nm, and 28.540 nm, respectively. The hardness of the NiS - 0, NiS - 8, and NiS - 14 samples are 212.33 HV, 255.01 HV, and 267.214 HV, respectively. Higher hardness could be reached by reducing the size of crystallites. The influence of the magnetic field could enhance hardness during the electroplating process.

Combined effects of magnetic and electric fields on the interband optical transitions in InAs/InP quantum wire

The ferrofluids synthesized from platelet magnets in liquid media are quite interesting due to their shape-induced magnetic response. In this paper, the magnetoviscosity of barium ferrite (BaM) ferrofluid is studied to understand the magnetic response of BaM platelet particles. The platelet particles were synthesized by the hydrothermal method and coated with oleic acid. The X-ray diffraction data confirm the platelets consisting of BaM phase. The field-emission scanning electron microscopy and transmission electron microscopy micrographs show hexagonal platelets of 3–5 nm thickness and 50–250 nm in size. The magnetization versus magnetic field plot shows hard ferromagnetic behavior of the nanoparticles. The ferrofluid was synthesized by dispersing coated platelets in paraffin. The flow curves of the ferrofluid exhibit shear thinning with power law behavior in the presence of magnetic field. The yield stress values are determined by extrapolating shear stress versus shear rate plots to zero shear rate at various applied magnetic field values using Herschel–Bulkley equation. The magnetoviscosity, $\eta $ , of the ferrofluid as a function of magnetic field is investigated at various shear rates. The $\eta $ value increases with the increase in magnetic field, reaches a maximum value and then saturates at higher fields. This trend is due to the alignment of platelet-shaped magnetic particles along the direction of magnetic field at different shear rates. With the increase in magnetic field, the interaction between the magnetic nanoparticles and their arrangement becomes stronger leading to stacked plate chain formation. This shows that the variation of magnetoviscosity as a function of shear rate can be controlled by competition between the flow field and the magnetic field.

The principle quantities which parameterize the antiferromagnetism of Cr are studied by neutron diffraction as a function of temperature, pressure, magnetic field, and concentration of solute atoms. In order to account for the observed intensities of the magnetic reflections, their dependence on magnetic field and temperature, the torque measurements of Montalvo and Marcus, and the creation of a ``single-Q'' state in field-cooling, a model is proposed based on the presumed existence of thermally active polarization domains within a ``single-Q'' region of the crystal. The variation of the polarization axis from place to place and with time lowers the free energy by an increase in entropy. The pressure dependence of the first-order phase change at 38.5°C is given as dTN/dP=−5.4 deg/kbar. The temperature dependence of the length of the wave vector below TN is given as (1/Q) (dQ/dT)=6.3×10−5 deg−1. Alloys with 0.5 and 0.78 wt% Fe and with 0.9 wt% Co show a decrease in TN of ∼20°K per at.% of solute. The amplitudes of the magnetization waves increase and the wave vector Q approaches commensurateness with the lattice periodicity with increasing solute concentration in contrast to results for other solutes. Some unusual effects were observed for 2.3 wt% Fe samples.

Four samples of austenite coatings deposited by reactive magnetron sputtering on silicon substrate at four different temperatures and pressures were investigated by ferromagnetic resonance (FMR) method at room temperature. The expanded austenite phase S (γ N) layers with thickness in the 160–273 nm range and concentration of magnetic atoms: 72 % Fe, 18 % Cr and 10 % Ni, were obtained. The coatings with nanometric size grains were strongly textured and grown mostly in [100] direction, perpendicular to the sample surface. Intense FMR spectra were recorded at various angles between the static magnetic field direction and the sample surface. A strong magnetic anisotropy of the main uniform FMR mode was observed and the effective magnetization 4πM eff determined. Spin wave resonance (SWR) modes were observed in all investigated samples in out-of-plane geometry of the magnetic field. The resonance fields of SWR modes in our samples varied linearly with the spin wave mode number. The value of the effective magnon stiffness constant was determined assuming a parabolic shape of the magnetization variation across the sample thickness.

Heat capacity and entropy of two electrons quantum dot in a magnetic field with parabolic interaction

Spin orientation in charge-tunable InP quantum dots