Values Of External Magnetic Field Research Articles

Monte Carlo simulation study of magnetocaloric effect in NdMnO3 perovskite

The magnetocaloric effect in NdMnO3 perovskite is investigated by using the Monte Carlo simulations. The Curie temperature TC of NdMnO3 compound is deduced from the variation of the magnetization vs. the temperature with different values of external magnetic field. The variation of magnetization with the external magnetic field H is given. The specific heat with the temperature is established for different external magnetic field. The thermal magnetic entropy for different external magnetic field and different exchange interactions in NdMnO3 compound is obtained. The adiabatic temperature change is obtained. The relative cooling power with different external magnetic field is established. The magnetocaloric effect has been investigated from magnetization.

Monte Carlo Simulation Study of Magnetic Properties of Li 3 V 2(PO4)3

The magnetic properties of Li3V2(PO4)3 in the presence of a dependent magnetic field, exchange interactions, and crystal field are studied by using the Monte Carlo simulations. The thermal magnetizations and magnetic susceptibilities of Li3V2(PO4)3 are given with different values of exchange interactions, crystal field, and external magnetic field. The critical exponent associated with the magnetization and with magnetic susceptibilities is given for different values of exchange interactions, crystal field, and magnetic external field. The magnetic hysteresis cycle with the reduced temperatures, the exchange interactions, and the crystal field is established.

Ferromagnetic and antiferromagnetic order analysis of Fe- and FeO-modified Graphene-nano-ribbon: A Monte Carlo simulation study

The magnetic properties of Fe- and FeO-modified Graphene-nano-ribbon: C32H2Fe2 and C32H2Fe2O2 are studied using Monte Carlo simulations. The thermal magnetization and magnetic susceptibility with different values of exchange interactions, zero crystal field and zero magnetic field are established. The transition temperature is deduced for different values of exchange interactions. The internal energy, magnetization with a fixed value of exchange interactions, zero crystal field and external magnetic field are given. The magnetization versus the exchange interaction with different values of temperature, different values of crystal field and external magnetic field of are obtained. The magnetic hysteresis cycles have been deduced.

Thermal properties of [Cr(NH3)6](BF4)3 studied by adiabatic and relaxation calorimetry

Four (solid–solid) phase transitions were detected in the temperature range of (9 to 300)K in polycrystalline [Cr(NH3)6](BF4)3 at TC1=240.7K, TC2=108.0K, TC3=91.9K, and TC4=61.3K by adiabatic calorimetry. The measurements by relaxation calorimetry were followed on lowering temperature from 20K down to 0.35K under six different external magnetic field values (9, 7, 5, 3, 1 and 0)T. For non-zero values of applied magnetic field well-defined Schottky anomaly appears. Magnetic heat capacity was calculated assuming the zero-field splitting for the decoupled Cr(III) ions. There is no discrepancy between the observed and calculated values. Isothermal magnetization curve recorded up to 5T was measured at temperature of 1.8K.

Current-driven vortex domain wall motion in wire-tube nanostructures

We have investigated the current-driven domain wall motion in nanostructures comprised of a pair of nanotube and nanowire segments. Under certain values of external magnetic fields, it is possible to pin a vortex domain wall in the transition zone between the wire and tube segments. We explored the behavior of this domain wall under the action of an electron flow applied in the opposite direction to the magnetic field. Thus, for a fixed magnetic field, it is possible to release a domain wall pinned simply by increasing the intensity of the current density, or conversely, for a fixed current density, it is possible to release the domain wall simply decreasing the magnetic external field. When the domain wall remains pinned due to the competition between the current density and the magnetic external field, it exhibits a oscillation frequency close to 8 GHz. The amplitude of the oscillations increases with the current density and decreases over time. On the other hand, when the domain wall is released and propagated through the tube segment, this shows the standard separation between a steady and a precessional regime. The ability to pin and release a domain wall by varying the geometric parameters, the current density, or the magnetic field transforms these wire-tube nanostructures in an interesting alternative as an on/off switch nano-transistor.

Important defeats on pinning of 2D pancake vortices in highly anisotropic Bi-2212 superconducting matrix with homovalent Bi/La substitution

This comprehensive study aims to investigate the change of the flux pinning mechanism, electrical and superconducting properties of the inorganic solid Bi-2212 materials with the La inclusions inserted in the crystal structure by means of magnetotransport measurements exerted in the applied magnetic field range of 0—7T. Crucial characteristics as regards critical transition temperatures (Tconset and Tcoffset), room temperature resistivities (ρ300K), residual resistivities (ρ0), residual resistivity ratios (RRR), irreversibility fields (μ0Hirr), upper critical fields (μ0Hc2), thermodynamic critical fields (μ0Hc), activation energies (U0), penetration depths (λ) and coherence lengths (ξ) are evaluated from the experimental magnetoresistivity curves and available theoretical approaches. All the properties obtained above confirm the considerable degradation in the pinning of 2D pancake vortices with the increment of the La individuals randomly distributed in the Bi-2212 superconducting system. Thus, the improved recoupling linelike nature among the consecutively stacked layers leads to decoupling of the adjacent layers and suppression of the interlayer Josephson coupling length as a result of the enhancement in the thermal fluctuations of flattened pancake vortices. The long and short of it is that the La impurities undermine the elasticity of the vortex lattice. For example, the Tcoffset and Tconset values are found to be about 84.5K and 85.7K for the best (pure) sample while the material exposed to the La content level of x=0.2 obtains the values of 82.2K and 15.1K, respectively at zero applied magnetic field. In the case of the applied magnetic field of 7T, the Tcoffset value reduces considerably towards the lower temperature values of 72.6K for the former compound. However, the values belonging to the worst sample (La4) cannot be determined at higher external magnetic field value such as 1T due to the hybridization of La-3/states with the Cu3d–O2p states in the Cu–O2 layers (dissipation). This is attributed to the existence of the pair-breaking mechanism in Bi-site La substituted Bi-2212 systems. Moreover, the flux pinning energy values calculated from thermally activated flux flow (TAFF) model decrease dramatically with the enhancement of both the La content level and external magnetic fields. Numerically, the activation energy value is calculated to be about 5173K (1077K) for the pure sample at the field value of 0T (7T) whereas the values pertaining to the compound substituted by the La concentration level of x=0.15 are found to be in a range of 1196–281K. The lack of the experimental evidences does not enable us to find the energy values belonging to the La4 sample at higher applied field. As for the critical field parameters (μ0Hc1, μ0Hc, μ0Hirr, μ0Hc2 and μ0Hc3) and the extracted values (λ, ξ and κ), the changes in the parameters given also verify the degradation of the flux pinning ability (random distribution of the artificial pinning centers) with the La concentration as a result of the Cooper pair-breaking mechanism. To sum up, the La impurities are unfavorable for the potential applications of these materials in the commercial sector at high temperatures and magnetic fields.

Strong enhancement of Faraday rotation using one-dimensional conjugated photonic crystals containing graphene layers.

We propose a one-dimensional conjugated photonic crystal single heterojunction infiltrated with a single graphene layer to achieve large Faraday rotation (FR) angles as well as high transmission simultaneously. The effects of the external magnetic field values, incidence angle, number of unit cells, layer thickness of constituents of the conjugated photonic crystals, chemical potential of graphene, and ambient temperature on the Faraday rotation angle and transmission are investigated. Our results reveal that both the sign reversal and shifting of the FR peak can be obtained by changing the width of layers in the conjugated photonic crystal. In the case of negative FR angle, an increase of magnetic field enhances the FR angle and degrades the transmission. However, in the case of positive FR angle, when the magnetic field increases to a certain value, the FR angle is improved too. Further increase of the magnetic field leads to a decrease of FR angle. With increasing the number of unit cells, the FR angle is enhanced at the cost of decreasing the transmission. It is shown that normal incidence results in higher FR angle and transmission. It is also demonstrated that sign reversal and change of the FR angle is possible by manipulating the chemical potential of graphene and the ambient temperature.

Self-Generation of Parametric Soliton-Like Pulses in a Magnonic Quasi-Crystal Active Ring Resonator

This paper reports theoretical results of a parametric soliton-like pulse self-generation in an active ring resonator by using magnonic quasi-crystal (MQC) with Fibonacci-type structure. For the calculation of MQC transmission responses, the model based on the transfer matrix method is used. Besides, the model of the MQC active ring resonator that contains three perimetrically coupled differential equations and two differential equations of linear oscillators is used to calculate the parametric soliton-like pulse self-generation. It is established that such pulses are self-generated all over the range of the external static magnetic field values where three-wave parametric decay of the magnetostatic surface wave is allowed. The minimal threshold of the soliton-like pulse self-generation is observed at high values of a magnetic field. This threshold is increased at any value of a magnetic field when a magnonic crystal is used in a feedback loop.

NUMERICAL CALCULATION OF INTERNAL INDUCED FIELDS IN HUMANS DUE TO HIGH VOLTAGE TRANSMISSION LINES

Interaction of extremely low frequency (ELF) electromagnetic fields (EMF) with human has been a great concern over the previous years for researchers. ELF EMFs emanating from high voltage transmission lines interact with human by inducing electric fields internally in body. Various studies have shown the ill effects of this interaction on human organism. In this paper, numerical calculations of internally induced electric field and current density in human of different gender and age are done. Maximum values of external electric and magnetic fields are estimated from the detailed survey carried out on 132 kV high voltage transmission line. Human body is a complex structure comprising of several tissues with varying values of conductivity and relative permittivity. It is very difficult to describe the interaction of external fields with every single tissue and no direct method is available for measurement of internally induced fields. Internal fields are estimated with the help of homogeneous ellipsoid model. The total induced electric field and current density due to combined effect of external electric and magnetic field is calculated. Results obtained are compared with recommended exposure levels.

Morphological Properties And Birefringences Of Uniaxial Lyotropic Nematic Mesophases Under Influence Of Various Magnetic Field Values

One has studied time-dependent changes of morphological properties of uniaxial lyotropic nematic-calamitic NC and nematic- discotic ND mesophases with various external magnetic field values. Also, changes of optical birefringence values of NC and ND lyotropic mesophases under influence of the magnetic fields has been investigated based on time. Differences of morphological properties and changing birefringence values between NC and ND mesophases have been interpreted according to magnetic field values. The values of optical birefringence and morphological properties changing in time between NC and ND mesophases which are opposite signs of diamagnetic anisotropy have been compared with increasing magnetic field values.

Numerical simulation of graphene in an external magnetic field

In this paper the results of numerical simulation of monolayer graphene in external magnetic field are presented. The numerical simulation is performed in the effective lattice field theory with noncompact $3 + 1$-dimensional Abelian lattice gauge fields and $2 + 1$-dimensional staggered lattice fermions. The dependences of fermion condensate and graphene conductivity on the dielectric permittivity of substrate for different values of external magnetic field are calculated. It is found that magnetic field shifts insulator-semimetal phase transition to larger values of the dielectric permittivity of substrate. The phase diagram of graphene in external magnetic field is drawn.

Non-linear behavior of coercivity to the maximum applied magnetic field in La substituted nanocrystalline cobalt ferrite

The magnetic properties of nanocrystalline cobalt ferrite could be tuned with substituting small amount of non-magnetic rare earth cation at Fe site in cobalt ferrite. The variation in magnetic parameter of samples could also be obtained by measuring its anhysteretic magnetization curve without tailoring its chemical composition. The magnetic parameters such as coercivity, remanent magnetization and saturation magnetization critically depend upon different values of external magnetic fields. In the present study, the anhysteretic magnetization curve of the samples CoFe2−xLaxO4 (x=0.025, 0.05, 0.075 and 0.1) has been recorded and response of coercivity to different maximum values of applied field has been investigated. It has been observed that the response of coercivity to different maximum values of applied field shows non-linear behavior. The analysis of the response of coercivity to different values of applied field in low field regime has been carried out with the help of Rayleigh laws. The analysis of the plot yields significant information about magnetic anisotropy.

On the ordinary mode and whistler mode instabilities in the degenerate anisotropic plasmas

Employing Vlasov-Maxwell set of equations, we have investigated the O-mode and whistler mode instability in a degenerate anisotropic magnetoplasma environment and compared the results to those reported for classical plasmas. We propose the excitation of a new banded type of instability for the O-mode case, which grows at some particular values of temperature anisotropy and external magnetic field. For the case of whistler wave, we observe instability saturation mechanism similar to the case of classical plasmas. The existence of both O-mode and whistler mode instability has been observed only for some specific range of unstable wavenumbers. The possible excitation of such instabilities in solid state plasma has been discussed, particularly for semiconductor and semimetal plasmas.

Local Study of Magnetic Structures in High-Temperature Superconducting Composites

The results of magneto-optical investigations of the magnetization processes in high-temperature superconducting coated conductor composites are presented. The studies were performed in the temperature range of 4–80 K. It is shown that the re-magnetization of composites in external magnetic field is accompanied by formation and propagation of the magnetic flux annihilation waves (areas with zero magnetic induction). The relationship between penetration depth of annihilation front and the value of external magnetic field at different temperatures as well as temperature dependence of the rate of magnetic flux annihilation front motion are found. The experimental data agree qualitatively with the results of numerical calculations performed by using the Monte Carlo method.

DEPENDENCE OF ASYMMETRIES FOR CHARGE DISTRIBUTION WITH RESPECT TO THE REACTION PLANE ON INITIAL ENERGY IN HEAVY-ION COLLISIONS

In this paper, two combinations of correlators are defined in order to investigate the evolution of possible [Formula: see text] invariance violation in strong interactions with initial energy for heavy-ion collisions. These combinations correspond to absolute and relative asymmetry of distribution of electrically charge particles with respect to the reaction plane in heavy-ion collisions. Energy dependence of parameters under study was derived from data of STAR and ALICE experiments. Significant decreasing both absolute and relative asymmetry is observed at energies [Formula: see text]. This feature agrees qualitatively with other results of stage-I beam energy scan program in STAR experiment. General behavior of dependence of absolute asymmetry on initial energy agrees reasonably with behavior of similar dependence of Chern–Simons diffusion rate calculated at different values of external Abelian magnetic field. The observed behavior of parameters under study versus energy can be considered as indication on possible transition to predominance of hadronic states over quark–gluon degrees of freedom in the mixed phase created in heavy-ion collisions at intermediate energies.

Magnetoelectric susceptibility tensor of multiferroic TbMnO3 with cycloidal antiferromagnetic structure in external field

Magnetoelectric, dielectric, and magnetic susceptibility tensors of multiferroic TbMnO3 with cycloidal antiferromagnetic structure in external electric and magnetic fields have been investigated with taking into account dynamics of spin, electro-dipole, and acoustic subsystems. All components of tensors depend on values of external electric and magnetic fields. The possibility of control of electrodynamic properties of multiferroic TbMnO3 with cycloidal antiferromagnetic structure by external electric and magnetic fields has been shown. The resonant interaction of spin, electro-dipole, electromagnetic, and acoustic waves in such material is observed.

Velocity-selective double resonance in Doppler-broadened rubidium vapor

We study resonantly enhanced cascaded two-photon transitions in Doppler-broadened rubidium vapor, induced by an optical frequency comb. Cascaded two-step excitation of atoms from the ground state 5$S$${}_{1/2}$ to the final 5$D$${}_{5/2}$ state via an intermediate 5$P$${}_{3/2}$ state as well as the influence of the frequency comb repetition rate on the two-photon fluorescence signal have been investigated. It is shown that the careful choice of ${f}_{R}$ leads to enhancement of the two-photon signal with considerable increase of the final $5{D}_{5/2}$-state population due to velocity-selective double resonance. Since the double-resonance condition for two different rubidium isotopes is fulfilled for different ${f}_{R}$, the possibility of isotope-selective two-photon excitation is explored. The dependence of the two-photon signal on external magnetic field values and different repetition rates of the optical frequency comb is also investigated.

Effect of self-magnetic fields on the nonlinear dynamics of relativistic electron beam with virtual cathode

The report is devoted to the results of the numerical study of the virtual cathode (VC) formation conditions in the relativistic electron beam (REB) under the influence of the self-magnetic and external axial magnetic fields. The azimuthal instability of the relativistic electron beam leading to the formation of the vortex electron structure in the system was found out. This instability is determined by the influence of the self-magnetic fields of the relativistic electron beam, and it leads to the decrease of the critical value of the electron beam current (current when the non-stationary virtual cathode is formed in the drift space). The typical dependencies of the critical current on the external uniform magnetic field value were discovered. The effect of the beam thickness on the virtual cathode formation conditions was also analyzed.

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.

Size effect on magnetic properties of a nano-graphene bilayer structure: A Monte Carlo study

In this paper we use the Monte Carlo simulations to investigate the magnetic properties of an Ising ferromagnetic–antiferromagnetic model. The system is based on a nano-graphene structure-like bilayer with two bloc sizes: N=24 and 42 spins. For each size N, the upper layer A is formed with spin −3/2, whereas the lower layer B is composed of spin −5/2. We only consider the first nearest-neighbor interactions between the sites i and j. The magnetic properties are studied, in the absence as well as in the presence of a crystal magnetic field, and an external magnetic field. The increasing temperature and crystal field as well as the inter-layer coupling constant, are also studied for this system sizes N=24 and 42 spins. The zero-field-cooled and the field cooled magnetization behaviors are investigated for different values of external magnetic field and a fixed value of exchange interaction between the two blocs. The magnetizations as well as the magnetic susceptibilities versus the temperature are used in order to obtain blocking temperature.The saturation magnetization and coercive field are also obtained for the two sizes of the studied system. It is found that the blocking temperature decreases on increasing the crystal magnetic field and/or the external magnetic field, for a fixed system size. On the other hand, it is found that the blocking temperature increases on increasing the system size from N=24 to 42 spins, for fixed values of external and the crystal magnetic fields.