External Magnetic Eld Research Articles

Super dense coding in one-axis twisting model

We study thermal dense coding in a two-spin model under an external magnetic eld. Its depen-dencies on magnetic eld, strength of the spin squeezing and temperature are presented in detail.Our main goal now is to study how we can increase the thermal dense coding capacity in the presenceof magnetic eld, strength of the spin squeezing and temperature. It shows that the dense codingtend to valid value by setting the value of the input quantum correlations. Our most importantmotive for this study is to examine the relationship between the thermal properties of super quan-tum discord (SQD) and dense coding. The results show that the thermal properties of the SQD onour channel enable us to determine when and under what conditions the system is suitable for validdense coding. Our proposals could be lead to that this scheme is efficient for quantum informationprocessing.

Soliton surfaces induced by the coupled integrable dispersionless equation with self-consistent sources

The coupled integrable dispersionless equations have a signi cant interest because of structure, integrability, and the possibility of obtaining a soliton solution. In this paper, we construct soliton surfaces for integrable dispersionless equation with self-consistent sources in Riemann space. The surfaces, arising from M-XXXII equation and their reduction in R3, are studied. We obtain Gaussian and mean curvatures and also evaluate the area of surface parametrically de ned with the Riemannian metric. Using the scale transformation and transformation of dependent and independent variables of the coupled dispersionless equations we obtain the equation that describes a current-fed string interacting with an external magnetic eld in three-dimensional Euclidean space.

Unsteady double-diffusive natural convection with Soret and Dufour effects inside a two-sided lid-driven skewed enclosure in the presence of applied magnetic field

This article describes the heat and mass transfer as well as the entropy generation in an unsteady double-diffusive natural convection in the presence of an external magnetic eld, Soret and Dufour e ects. The analysis uses a two- dimensional skewed enclosure, where the inclined walls make a skew angle  with x-axis. The governing equations in the physical domain are transformed into an orthogonal computational domain by co-ordinate transformations, and then are solved using a nite volume method based on SIMPLE algorithm. The computations are carried out in the six skewed enclosures with skew angles  = 15, 30, 45, 60, 75, and 90, for a wide range of the Hartman number, Lewis number, buoyancy ratio, and Dufour coecient, while Soret coecient is kept constant at 0.25 in most of the study. Results show that the fluid flow, heat and mass transfer, as well as the entropy generation are sensible to some extent to the skew angle variation. Meanwhile, the Lewis number and buoyancy ratio have an aiding and opposing action, respectively, on suppression eff ect of Lorentz force against convective heat and mass transfer. It is also shown that the average entropy generation is an increasing function of Lewis number, buoyancy ratio, and Dufour coecient, while its a decreasing function of Hartman number.

QUANTUM DOTS IN FERROMAGNETIC HEISENBERG MODEL

Quantum Dots (QDs) are semiconductor-nanostructure materials which are also called arti cial atoms. QDs are classi ed as ferromagnetic material. Theoretically, Heisenberg model is regarded as a good model in describing these QDs. We applied Spin Wave Theory (SWT) on the above mentioned model to explore the physical properties of these materials, such as ground state energy, excitation energy and magnetization. We found that the ground state energy "g increased with the applied external magnetic eld B as B0:3. A phase transition was also observed around B~1T, which indicate a transition from singlet to a triplet state. Staggered magnetization reaches saturation around this point of transition.

POLARIZATION TRANSFORMATION BY A HYPERBOLIC METAMATERIAL ON A METAL SUBSTRATE

In the present paper we focus on the study of polarization properties of biaxial metamaterial, which consist of alternate ferrite and semiconductor layers, located on an ideally conducted metal substrate. The system is placed into an external magneticeld along the boundaries of the layers. The effective medium theory is applied. Effective linear-to-ellipt polarization conversion has been shown, by means of physical and geometrical parameters of the system under consideration.

The Effects of the Random Transverse Crystal Field on the Spin-1 Model

The e ects of random transverse crystal eld are investigated in the meaneld approximation on the spin-1 model. The transverse crystal eld is applied on a lattice in a bimodal random distribution with a tunable parameter adjusting the strength of one mode with respect to the other one. Then, the phase diagrams are calculated on the reduced temperature-transverse crystal eld planes for given values of probability p and coordination number q at zero external magnetic eld h. It was found that the model gives both secondand rst-order phase transitions and tricritical points which is a well-known behavior of the spin-1 model. In addition, the model also yields critical end points and end points for the rst-order phase transition lines for appropriate p values.

Andreev Transport in Double Quantum Dot Cooper Pair Splitters in the Presence of External Magnetic Field

The e ect of external magnetic eld on the transport properties of double quantum dots coupled to normal and superconducting leads is studied by means of the real-time diagrammatic technique in the sequential tunneling regime. This device works as a gate-controlled Cooper pair splitter. We focus on the transport regime where the current is blocked due to the spin triplet blockade. It is shown that external magnetic eld can modify the Andreev current and di erential conductance. In particular, magnetic eld can suppress the negative di erential conductance associated with the triplet blockade.

The Magnetic Field Effects on Spin Polarization of T-Shaped Double Quantum Dots Coupled to Ferromagnetic Leads

We analyze the spin-dependent conductance and spin polarization of a double quantum dot in a T-shape conguration coupled to ferromagnetic leads in the presence of external magnetic eld. The calculations are performed with the aid of the numerical renormalization group method. We show that in the antiparallel con guration, nite magnetic eld can give rise to the full spin polarization of the current, which can be controlled by tuning the dots' levels. On the other hand, for parallel con guration enhanced spin polarization can be generated by an exchange eld due to the presence of ferromagnetic leads and can be also tuned by changing level position or external magnetic eld. The magnetic eld can be thus used to improve the spin-resolved properties of the system.

Electromagnetic Waves Absorption by Graphene-Magnetic Semiconductor Multilayered Nanostructure in External Magnetic Field: Voight Geometry

Absorption of electromagnetic waves by graphene magnetic semiconductor multilayered structure has been investigated for the Voight geometry with taking into account the dissipation processes. The possibility of control of electrodynamic properties of the structure by an external magnetic eld, changing in number of periods of the structure, chemical potential of the graphene layers and temperature has been shown. Electrodynamics of the structure is also sensitive to polarization of the incident wave. The structure shows to be especially controllable at terahertz frequencies.

Second-Harmonic Generation Studies of Inhomogeneous Magnetization Distributions in Thin Garnet Film

The magnetization processes can be e ectively studied using magnetization-induced second-harmonic generation e ect (MSHG). The aim of the current work is the investigation of inhomogeneous magnetization distributions induced in the surface area of the garnet lm by ion implantation. The studies were performed on magnetic garnet lm of (111) symmetry, implanted with H+2 ions of 1.5 × 10 cm−2 dose and 60 keV energy. The measurements of MSHG e ect were performed as a function of the sample rotation angle and the amplitude of external magnetic eld. The observed MSHG intensity hystereses were subjected to a decomposition procedure into contributions having di erent magnetic eld dependences. The contributions originating from the implanted and unimplanted parts of the lm volume of di erent magnetic ordering were analyzed and discussed.

Dielectric Properties of Lyotropic Magnetic Liquid Crystal

Dielectric Properties of Lyotropic Magnetic Liquid Crystal P. Kop£anský, L. Tom£o, J. Jadzyn, J. Swiergiel, J. Majoro2ova, M. Kubov£ikova, M. Timko, M. Raj¬ak, K. ’ipo2ova, Z. Gaoova, Z. Bednarikova, N. Toma2ovicova, Chin-Kun Hu, S. Hayryan, I. Studenyak , T.M. Kovalchuk and O.V. Kovalchuk Institute of Experimental Physics, Slovak Academy of Sciences, Ko2ice, Slovakia Faculty of Aeronautics, Technical University, Ko2ice, Slovakia Institute of Molecular Physics, Polish Academy of Sciences, Pozna«, Poland Department of Biochemistry, Institute of Chemistry, P.J. Safarik University in Ko2ice, Slovakia Institute of Physics, Academia Sinica, 128 Sec.2, Academia Rd., Nankang, Taipei 11529, Taiwan Physics Faculty, Uzhhorod National University, Uzhhorod, 88000, Ukraine Institute of Semiconductor Physics, National Academy of Science of Ukraine, Kyiv, Ukraine Kyiv National University of Technologies and Design, Kyiv, Ukraine An important feature of lyotropic liquid crystals is the self-assembly of the amphiphilic molecules as supermolecular structures. We have studied the formation of nematic liquid crystal phase in solutions containing lysozyme amyloid brils and magnetic nanoparticles using oscilloscopic method. Interaction of brils with magnetic nanoparticles under the external magnetic eld resulted in bril re-arrangement. The analysis of the obtained results suggests that the decrease in conductivity of solutions in presence of magnetic eld is due to decrease of the ion mobility caused by re-arrangement of structures in the solution. The obtained results allow determination of the optimum ratio of the components which can lead to preparation of solutions with a more ordered structure in presence of magnetic eld.

High Resolution Tips for Switching Magnetization MFM

Switching magnetization magnetic force microscopy (SM-MFM) is based on two-pass magnetic force microscopy with opposite orientation of tip magnetization between two scans. The sum of the scanned data with reversed tip magnetization depicts local van der Waals forces, and their di erence maps the local magnetic forces. Tip magnetization can be easily reversed in external magnetic eld during the scanning. The separation of the forces mapped enables scanning in close proximity of the sample (∼ 5 nm). Therefore, extremely high spatial resolution (10 nm) is achievable by the SM-MFM. Image phase resolution of the MFM method depends on various geometric parameters of the tip, such as tip length, its apex radius and taper angle. The parameters are determined by the evaporation process, within which the standard atomic force microscopy tips are coated with magnetic layer. In this work we show that the thickness of the coated layer is important for the SM-MFM spatial resolution.

Influence of Magnetic Field on Dielectric Breakdown in Transformer Oil Based Ferrofluids

In this paper the experimental study of the breakdown eld strength in a transformer oil based ferro uid is reported. The experiments are conducted on ve ferro uid samples with di erent magnetic volume fraction. The in uence of external magnetic eld on the breakdown eld strength is investigated, when a quasi-homogenous magnetic eld was applied in parallel and perpendicular con guration in regard to the electric eld. The obtained results are analysed in accordance to the electron charging of ferro uid nanoparticles theory.

Imaging of Magnetic Domains and Domain Walls in Spherical Fe-Si Powder Using Magnetic Force Microscopy

The commercial Fe-Si powder, produced by Hoganes Corporation, represents promising soft magnetic material for technological applications. The powder consists of spherical particles with diameter up to 150 μm. Internal microstructure of the powder is formed by grains of diameter of about 30 μm. Each separate grain has a random orientation of the easy magnetization axis and is su ciently large to split into several magnetic domains. A comparative study of the atomic force microscopy (AFM) topography and the corresponding magnetic force microscopy (MFM) images was employed in order to examine the correlation between the grain size, boundaries of grains and characterization of the magnetic domains, which gives us an important knowledge about possible behavior of particles under the in uence of the external magnetic eld and further utilization of the spherical Fe-Si particles in electrotechnical industry. The grain size and the crystallographic orientation of grains were analyzed by the electron backscattering di raction (EBSD) technique.

Magnetization and Susceptibility of a Diluted Triangular Ising Antiferromagnet in a Field

Within the framework of the e ectiveeld theory with correlations we investigate e ects of an external magnetic eld and random site dilution on basic thermodynamic quantities, such as the magnetization and the magnetic susceptibility, on the geometrically frustrated triangular lattice Ising antiferromagnet. Behavior of these quantities is presented in the temperatureeld parameter space for selected mild degrees of dilution. It is found that, besides the anomalies associated with phase transitions from the ferrimagnetic to the paramagnetic state, in certain regions of the parameter space these functions display some more anomalies and peculiarities, as a result of joint e ects of the geometrical frustration, magnetic dilution, thermal uctuations and the applied magnetic eld.

Magnetic Properties of Epitaxial Fe/(Ga,Mn)As Hybrids

Thinlm structures composed of two kinds of ferromagnetic material metallic Fe and semiconducting (Ga,Mn)As were investigated by means of SQUID magnetometry and ferromagnetic resonance spectroscopy. Dependence of remnant magnetic moment on temperature showed unexpected anisotropic features when recorded along two orthogonal in-plane directions. For one of these orientations, the change in sign of the slope of m(T ) curve at the Curie point of (Ga,Mn)As was observed, while for the other, an analogous m(T ) curve retained monotonic character. Based on the comparison with ferromagnetic resonance data, the apparent non-monotonicity was attributed to the temperature-induced change of balance between the external magnetic eld and uniaxial magnetic anisotropy in the plane of Fe layer.

Magnetic Properties of RIrSi (R = Tb, Dy, and Ho) Compounds

The magnetic data for the polycrystalline samples of RIrSi (R = Tb, Dy and Ho) compounds are reported. These compounds are antiferromagnets with the Neel temperatures equal to 32 K (R = Tb), 7.0 K (R = Dy) and 4.8 K (R = Ho), respectively. The external magnetic eld induces the one step for TbIrSi and two step for DyIrSi and HoIrSi metamagnetic phase transitions. The values of the critical eld as Neel temperatures decrease with increase of the number of 4f electrons. The magnetic phase diagrams (H,T ) are determined.

Materials Bound by Non-Chemical Forces: External Fields and the Quantum Vacuum

We discuss materials which owe their stability to external elds. These include: 1)external electric or magnetic elds, and 2) quantum vacuum uctuations in these elds inducedby suitable boundary conditions (the Casimir e ect). Instances of the rst case include theoating water bridge and ferrouids in magnetic elds. An example of the second case is takenfrom biology where the Casimir e ect provides an explanation of the formation of stackedaggregations or \rouleaux" by negatively charged red blood cells. We show how the interplaybetween electrical and Casimir forces can be used to drive self-assembly of nano-structuredmaterials, and could be generalized both as a probe of Casimir forces and as a means ofmanufacturing nanoscale structures. Interestingly, all the cases discussed involve the generationof the somewhat exotic negative pressures. We note that very little is known about the phasediagrams of most materials in the presence of external elds other than those represented bythe macroscopic scalar quantities of pressure and temperature. Many new and unusual statesof matter may yet be undiscovered.

Monte Carlo Simulations of Ferromagnetic Nanocomposites

We present results of Monte Carlo simulations of a model system of Co nanoparticles in an external magnetic eld. In our simulations we take into account the interaction with the external magnetic eld, the energy of crystallographic anisotropy and the dipole dipole interactions between single domain nanoparticles. We apply the standard Metropolis algorithm to a cluster of 27 randomly distributed superparamagnetic Co nanoparticles. We investigate the dependence of blocking temperature TB on particle and cluster size.

Renormalization Group Approach for the Double Exchange Ferromagnets

The discovery of the colossal magnetoresistance (CMR) in the manganese oxides with perovskite structures T1−xDMnO3 (T = La, Pr, Nd; D=Sr, Ca, Ba, Pb) and its potential technological application motivated theoretical and experimental researchers to study the itinerant ferromagnetism. A rst theoretical description of this phenomenon in terms of the double-exchange mechanism was given a long time ago by Zener. In this model, the spin orientation of adjacent Mn-moments is associated with kinetic exchange of conduction eg electrons. Consequently, alignment of the core Mn-spins by an external magnetic eld causes higher conductivity. The Mn ions are considered as localized forming a spin of S = 3 2 and they are coupled to the itinerant electrons by a strong ferromagnetic Hund coupling, JH > 0. We apply the ow equation technique (nonperturbative method, based on continuous canonical transformation) to the double-exchange model for ferromagnetism described by the Kondo type Hamiltonian. We want to eliminate the interaction term responsible for non-conservation of magnon number and to take into account fermion and magnon degrees of freedom. We express the spin operators of Mn ions via the magnon operators (the Holstein Primako transformation) and investigate the magnon excitation spectrum determined by Green's function.