High External Magnetic Field Research Articles

Coherent forward-scattering spectra of Cs I 852.1-nm with a light-emitting diode and a diode laser in a Voigt configuration

The coherent forward scattering (CFS) spectra of Cs I 852.1-nm line was measured using a CFS spectrometer in a Voigt configuration with an electromagnet and temperature-controlled Cs gas cell. A light-emitting diode (LED) and a diode laser (DL) were used as broadband and narrowband light sources, respectively. The relation of the CFS intensity and external magnetic field (B) was log–log plotted. Results showed that the CFS signal intensities depend on B to the power of 1.69 ± 0.38 and 1.51 ± 0.06 for DL and LED, respectively. A higher external magnetic field should be favorable when a broadband light source is used. However, the CFS signal decreased with an LED source as B approached 300 mT. To explain this observation, the hyperfine Paschen–Back splitting pattern of the Cs I 852.1-nm transition was calculated. The decrease in the CFS signal was caused by the level-crossing of π- and σ-components of the Cs I 852.1-nm transition in a Voigt configuration.

Optimization of power used in liver cancer microwave therapy by injection of Magnetic Nanoparticles (MNPs)

In this paper, the effects of the input power of a microwave antenna (MWAN) on liver cancer tissue when injected with Magnetic Nanoparticles (MNPs) are studied. First, for basic simulation, we validated our results by comparison with other literature data. After that, we used a 1.8-cm hepatocellular carcinoma (HCC) tumor, which was treated experimentally for 3-min ablation using MWAN operating at a frequency of 2.45 GHz with a power of 90 W. At the next step of the simulation, the obtained results were compared with experimental results. As a last step, the effects of various MWAN input powers on the tumor after injection of MNPs were studied. Our results show that MNPs can be used as excellent heat sources and reduce input power significantly to produce a similar hyperthermia. When maghemite γ-Fe2O3 MNPs are used, the input power decreases from 90 W to 35 W. In addition, it has been shown that using a higher external magnetic field can treat a larger tumor. The optimized simulated values of the external magnetic field and the input microwave power are 15 mT and 35 W, respectively.

Theoretical and computational study of instability in streaming negative ion plasma under static magnetic field

The instability and electrostatic wave modes generation in a cold negative ion plasma which streams across a static magnetic field has been analysed by fluid dynamical model and computer simulation technique. In the theoretical approach, we observed different kinds of acoustic modes and cyclotron modes at an oblique angle to the static magnetic field. At some critical wave number, the positive and negative ion acoustic modes split up into two, fast and slow waves. The value of critical wave numbers and wave growth rates depends on the plasma streaming velocity, electron concentration in the system, and magnetic field intensity. In the presence of high intense external magnetic fields, we observed a wave coupling between different electrostatic modes. With the help of computer simulation performed by the Particle In Cell method, we confirmed the presence of theoretically proposed wave modes and studied the evolution of instability in detail.

Anomalous magnetoresistance and magnetocaloric behaviour in layered intermetallic compound NdRu2Si2

The magnetoresistance (MR) and magnetocaloric properties of naturally occurring layered compound NdRu2Si2 with a Néel temperature TN = 24 K have been investigated in the temperature range 60 ≥ T ≥ 1.8 K. It has been shown that a high external magnetic field greatly modifies the MR properties of the compound which in its low temperature ferromagnetic state (T < 10 K) exhibits an unusual positive MR instead of being negative. Although, the magnetocaloric investigations at this field and temperature range further indicates that the compound is in a predominantly ferromagnetic state. With the lowering of temperature, the MR value changes from a negative 34% near TN to a positive 5% at 5 K. Magnetocaloric (MCE) investigations on NdRu2Si2 exhibit two well defined peaks corresponding to the magnetic transitions. A table like MCE behaviour has been observed in the temperature range from 5 K to 45 K.

Spatial configurations of topological defects in mesoscopic p-wave superconducting squares

In the framework of the microscopic Bogoliubov-de Gennes theory, we study the spatial configurations of topological defects under high external magnetic field in mesoscopic p-wave superconducting square systems. Besides the multivortex state with four conventional vortices, two novel types of multiskyrmionic states containing four separated coreless skyrmions with the topological charge Q = 2 or Q = 3 can be obtained as the ground states, accompanied with the half-quantum vortex-antivortex pair in one or two components of the order parameter. Moreover, when the superconducting pairing interaction is enlarged, more complex single or multiple skyrmionic structures as well as the skyrmion-vortex coexisting modes can remain (meta-)stable in the mesoscopic chiral sample.

Theoretical Analysis and PIC Simulation of a 220-GHz Second-Harmonic Confocal Waveguide Gyro-TWT Amplifier

Confocal gyrotron traveling-wave tube (gyro-TWT) is capable of operating in higher order modes, so it is attractive in high-frequency (> 100 GHz) band. However, the reported experimental and simulation results of confocal gyro-TWT usually operated at fundamental harmonic, so high external magnetic field was essential. In this paper, a second harmonic 220-GHz confocal gyro-TWT was designed through linear and nonlinear theory and particle-in-cell (PIC) simulation. The key problem of suppressing the backward-wave oscillations (BWOs) of both fundamental and second harmonics was solved by limiting the cavity length of the first section less than the critical BWOs length. In PIC simulations, the gyro-TWT operates at HE07 mode with an output power of 4.55 kW, the efficiency of 2.2% gain of 21.8 and the −3 dB bandwidth of 6 GHz. The calculated results from the nonlinear theory are in good agreement with the results from PIC simulation.

Mott insulator behavior in the yttrium-based antimoniate oxide Ba2YSbO6

A careful experimental and theoretical study of the double perovskite type material Ba2YSbO6 is reported. The results show that this yttrium-based antimoniate oxide crystallizes in a cubic structure, Fm3¯m (#225) space group, with evidence of the cationic ordering that characterizes a rocksalt superstructure, and tolerance factor slightly less than the unit (τ = 0.9791) due to the size differences between the Y-O6 and Sb-O6 octahedrons. The magnetic response shows weak ferromagnetic effects for the temperature values studied (50, 200 and 300 K), with evidence of an antiferromagnetic reentrance at T = 118 K under the application of low magnetic fields, which is attributed to the presence of polar ordering, accompanied by octahedral distortions caused by the movement of the cations Y3+ and Sb5+, whose effects are no longer observed in the presence of a fairly high external magnetic field (of the Tesla order). The results of the optical characterization by diffuse reflectance suggest the occurrence of a band gap Eg = 4.61 eV, which is characteristic of an insulating material. The electronic structure calculations corroborate the insulating nature of the Ba2YSBO6 complex perovskite. The results allow classifying this material as a Mott insulator, in which the occurrence of intra-site spin-exchange facilitates unpaired spins to the 4d-t2g Yttrium states, mediated by the 2p Oxygen orbitals and 5p Antimony orbitals, resulting in the ferromagnetic character of the insulating material.

Instrument to characterize the wetting behavior of molten metal on a solid substrate under high magnetic field.

A specially developed experimental platform to measure the wettability of molten metals on solid substrates under high magnetic fields in combination with the sessile drop method is presented in this work. The desired magnetic field was generated by a superconducting magnet containing a channel with a diameter of 300 mm, in which the main body of the experimental apparatus was installed. The developed setup was used to observe the in situ wetting behavior of a molten metal on a solid substrate and simultaneously record sample images in real time under a high magnetic field during the wetting process. Contact angles were determined by analyzing the recorded images with the help of analytical software. Experiments using a typical molten metal and a solid substrate were conducted. The results revealed that the wettability of the molten metal on the solid substrate was obviously improved under a high external magnetic field.

Enhancement of intrinsic magnetic damping in defect-free epitaxial Fe3O4 thin films

We have investigated the magnetic damping of precessional spin dynamics in defect-controlled epitaxial grown Fe3O4(111)/Yttria-stabilized Zirconia nanoscale films by all-optical pump-probe measurements. The intrinsic damping constant of the defect-free Fe3O4 film is found to be strikingly larger than that of the as-grown Fe3O4 film with structural defects. We demonstrate that the population of the first-order perpendicular standing spin wave (PSSW) mode, which is exclusively observed in the defect-free film under sufficiently high external magnetic fields, leads to the enhancement of the magnetic damping of the uniform precession (Kittel) mode. We propose a physical picture in which the PSSW mode acts as an additional channel for the extra energy dissipation of the Kittel mode. The energy transfer from the Kittel mode to the PSSW mode increases as in-plane magnetization precession becomes more uniform, resulting in the unique intrinsic magnetic damping enhancement in the defect-free Fe3O4 film.

Preparation, Crystal Chemistry, and Hidden Magnetic Order in the Family of Trigonal Layered Tellurates A2Mn(4+)TeO6 (A = Li, Na, Ag, or Tl).

We report the first four magnetic representatives of the trigonal layered A2M(4+)TeO6 (here, M = Mn) family. Na2MnTeO6 was synthesized from NaMnO2, NaNO3, and TeO2 at 650-720 °C, but analogues for which A = Li and K could not be obtained by direct synthesis. However, those for which A = Li, Ag, and Tl (but not K) were prepared by exchange reactions between Na2MnTeO6 and the corresponding molten nitrates. The oxygen content was verified by redox titration. According to the X-ray diffraction Rietveld analysis, the four new compounds are isostructural with Na2GeTeO6, trigonal ( P3̅1 c), based on ilmenite-like layers of edge-shared oxygen octahedra occupied by Mn(4+) and Te(6+) in an ordered manner. These layers are separated by cations A, also in a distorted octahedral coordination. However, off-center displacement of Tl+ is so strong, due to the lone-pair effect, that its coordination is better described as trigonal pyramid. Each MnO6 octahedron shares two opposite faces with AO6 octahedra, whereas TeO6 octahedra avoid sharing faces. Besides this double-layered structure, Na2MnTeO6 was often accompanied by a transient triple-layered rhombohedral polytype. However, it could not be prepared as a single phase and disappeared on annealing at 700-720 °C. All A2MnTeO6 samples (A = Ag, Li, Na, or Tl) revealed the unusual phenomenon of hidden magnetic order. Low-field magnetic susceptibility data exhibit a Curie-Weiss type behavior for all samples under study and do not show any sign of the establishment of long-range magnetic order down to 2 K. In contrast, both the magnetic susceptibility in sufficiently high external magnetic fields and the zero-field specific heat unambiguously revealed an onset of antiferromagnetic order at low temperatures. The frustration index f = Θ/ TN takes values larger than the classical values for three-dimensional antiferromagnets and implies moderate frustration on the triangular lattice.

Influence of high magnetic field on carbides and the dislocation density during tempering of high Chromium-containing steel

Abstract The influence of a 12 Tesla magnetic field on the microstructure of high Chromium-containing steel during tempering was investigated. The experimental results revealed that an external magnetic field significantly increases the number density of carbide (Fe, Cr)3C and the dislocation density. The external magnetic field decreases the Gibbs free energy of (Fe, Cr)3C and then decreases the nucleation barrier; hence, the number density of (Fe, Cr)3C increases by approximately 2.42 times. The higher number density of carbides doubles the dislocation density, corresponding to the larger critical unpinning stress τ c , which results in a dislocation pile-up in front of the carbides. The hardness change is negligible with an external 12 T magnetic field because the increment of hardness due to the denser carbides (Fe, Cr)3C and dislocations that originate from the 12 T magnetic field offsets the decrement of hardness that results from the decrease in the solid solution strengthening from the carbon atoms. The investigation of the impact of an external high magnetic field on the behavior of carbides and dislocations can provide a better understanding for the precipitation strengthening mechanism of nuclear fusion steels.

Magnetic-Field Tuning of Light-Induced Superconductivity in Striped La_{2-x}Ba_{x}CuO_{4}.

Optical excitation of stripe-ordered La_{2-x}Ba_{x}CuO_{4} has been shown to transiently enhance superconducting tunneling between the CuO_{2} planes. This effect was revealed by a blueshift, or by the appearance of a Josephson plasma resonance in the terahertz-frequency optical properties. Here, we show that this photoinduced state can be strengthened by the application of high external magnetic fields oriented along the c axis. For a 7T field, we observe up to a tenfold enhancement in the transient interlayer phase correlation length, accompanied by a twofold increase in the relaxation time of the photoinduced state. These observations are highly surprising, since static magnetic fields suppress interlayer Josephson tunneling and stabilize stripe order at equilibrium. We interpret our data as an indication that optically enhanced interlayer coupling in La_{2-x}Ba_{x}CuO_{4} does not originate from a simple optical melting of stripes, as previously hypothesized. Rather, we speculate that the photoinduced state may emerge from activated tunneling between optically excited stripes in adjacent planes.

The Spin‐Dependent Coupling in the Hybrid Quantum Dot–Majorana Wire System

The transport properties of a quantum dot coupled to two metallic contacts and side‐coupled to a topological superconductor wire hosting Majorana zero energy modes (Majorana wire) have been studied. The spin‐dependent tunneling amplitude between quantum dot and Majorana wire has been assumed. The polarization of tunneling amplitudes causes the polarization of spin‐dependent zero‐bias conductance, but the total conductance of a quantum dot depends very weakly on the polarization of tunneling amplitudes. The complex behavior of the zero‐bias anomaly of conductance in the presence of an external magnetic field is shown. The zero‐bias conductance peaks at high external magnetic field can be the fingerprint of the presence of Majorana fermions.

The magnetization of dense aggregated dipolar fluids

The magnetization for dipolar fluids is studied treated separately at low and high external magnetic field. Canonical ensemble Monte Carlo simulations have been performed in dipolar hard sphere fluid in order to test these theoretical results. New expressions are introduced at low and high external field and ultimately the synthesized formula is given. The main difference in the structure of dipolar liquids at different external field is the average orientation of the formed chains. In case of infinitesimal external magnetic field there is no a well-specified direction, while at high enough external field actually the chains are parallel to this field. The present theory yields good result in the intermediate region as well where the most conspicuous failures are provided by the former theories.

On the applicability of the electrodynamic approximation in the simulation of the electrovortex flow in the presence of an external magnetic field

Experimental and numerical results on the effect of an external axial magnetic field on the structure of the flow which occurs when an electric current passes through a conducting medium between two hemispheres are presented. Results show that for high external axial magnetic field it is absolutely necessary to take into account the induced currents generated by the flow. These results can be used in electrometallurgy for a priori estimates of the flow structure in the direct-current-arc furnaces.

Investigation of the magnetic and magnetocaloric properties in metamagnetic REFe2Si2 (RE = Pr and Nd) compounds

• Single phased PrFe 2 Si 2 and NdFe 2 Si 2 compounds were prepared. • Magnetic and magnetocaloric properties in PrFe 2 Si 2 and NdFe 2 Si 2 were studied. • Antiferromagnetic ordering at 8.5 and 15.5 K for RE = Pr and Nd, respectively. • Field-induced metamagnetic transition below T N for both compounds. • The origin of MCE and its potential application in RE Fe 2 Si 2 were discussed. The crystal structure, cryogenic magnetic and magnetocaloric properties in NdFe 2 Si 2 and PrFe 2 Si 2 compounds have been investigated. The NdFe 2 Si 2 and PrFe 2 Si 2 crystallized in the body-centered tetragonal structure with the space group of I4/mmm, and underwent first order magnetic transition from paramagnetic to antiferromagnetic (PM – AFM) around Néel temperatures T N of 8.5 K and 15.5 K, respectively. Under an applied-field change of ΔH = 5 T, the maximum values of magnetic entropy change (−Δ S M max ) are 6.4 J/kg·K and 12.4 J/kg·K for PrFe 2 Si 2 and NdFe 2 Si 2 , corresponding to relative cooling power ( RCP ) values of 0.8 J/cm 3 and 1.0 J/cm 3 , respectively. Moreover, under low applied field change and at low temperatures, the PrFe 2 Si 2 and NdFe 2 Si 2 show an inverse MCE because of the existence of the AFM ordering, while under high external magnetic field change, a normal reversible MCE is observed, which is caused by first-order magnetic transition from antiferromagnetic (AFM) to ferromagnetic (FM) state.

Performance evaluation of an energy meter for low-voltage system monitoring

The paper presents the design, realization and performance evaluation of an energy meter to be installed in LV power networks with specific features to be live-installable, with high accuracy and with high immunity vs. external electric and magnetic fields. The device can be controlled both through Bluetooth and Power Line Communications (PLC) protocols. Such an instrument has been commissioned by some main European utilities for online periodic comparison of energies and powers measured by smart energy meters installed in houses for billing purposes.

Electrothermal Modeling of Quench in REBCO Roebel Cables

The possibility of REBCO Roebel cables to carry a large amount of current in high external magnetic fields makes them suitable for application in future particle accelerator magnets. The physical phenomena related to the initiation and propagation of a quench event in Roebel cables have not yet been fully analyzed. In particular, given the peculiar architecture of these conductors, the features of the current redistribution and normal zone propagation after quench in individual tapes still require experimental and theoretical investigation. In this paper, an innovative quasi-3D electrothermal FEM model is developed to analyze the effect of quench in HTS Roebel cables. The model is based on a reduced dimensionality approach, under the assumption of a negligible thickness of the individual REBCO tapes. While the tapes are meshed in an identical 1-D pattern, the noncontinuous electrical and thermal contacts among them are accounted for as a sources in the corresponding thermal and electrical equations. Notwithstanding these significant assumptions, the main physical aspects involved in the quench initiation and propagation are retained and correctly described by the reduced dimensionality approach. The quench energy and the normal zone propagation velocity are analyzed for different cable configurations.

Surface Superconductivity in Ni50Mn36Sn14 Heusler Alloy

The changes in the magnetizations of Ni50Mn36Sn14 Heusler alloy (L21-NiMnSn-HA) with an antiferromagnetic interfacial exchange coupling have been investigated by using the effective field theory as a function of temperature and external magnetic field. It is shown that the Ni component is antiferromagnetic and its other components are ferromagnetic while the L21-NiMnSn-HA has a ferrimagnetic ordering below TC. And, they are paramagnetic above TC. The L21-NiMnSn-HA and its Ni component have the triple hysteresis loops below T* and the other components have only single hysteresis loop below TC. It is found that they exhibit type II/1 superconductivity at higher external magnetic field below T* and type II/2 superconductivity at lower external magnetic field above T*. Moreover, it is suggested that the surface superconductivity emerges below the conversion temperature of T∗≈ 0.74 and can be associated with the triple hysteresis loops which occur in the systems with an antiferromagnetic interfacial exchange coupling. And, the vortex state terminates at TV ≈ 4.37 for the Ni component of the L21-NiMnSn-HA. The HC-T phase diagrams of the L21-NiMnSn-HA and its Ni component are in qualitatively good agreement with the experimental and theoretical findings.

Morphology‐Dependent Magnetism in Nanographene: Beyond Nanoribbons

AbstractImprinting self‐sustainable magnetic features into graphene has recently generated much interest owing to its potential application in spintronics. Several strategies for imprinting magnetic features into graphene are proposed theoretically. However, only a few of them are realized experimentally. Here, the first scalable synthesis of magnetic graphene nanoplatelets with diverse morphologies, including nanoribbons and triangular, pentagonal, hexagonal, and other polyhedral shapes, is reported. This material enters the ferromagnetic regime at a temperature of ≈37 K with magnetization approaching ≈0.45 emu g−1 under high external magnetic fields. Theoretical calculations are used to explain this sort of morphology‐driven magnetism of graphene nanoplatelets, which emerges from the synergistic effects of the size, geometry of nanographenes, edge terminations, and angle between adjacent edges. In addition, they suggest a new way for preparing magnetically ordered graphene nanoplatelets with a higher transition temperature. In this respect, triangular motifs with zigzag edges represent the most promising morphology of graphene nanoplatelets, which can remain magnetically ordered up to ≈107 K. Based on these challenging results, further tuning of the size and morphology in spatially confined nanographenes combined with doping and sp3 functionalization will enable the preparation of magnetically ordered half‐metallic carbon sustainable up to room temperature, thus opening new opportunities in spintronics.