External Magnetic Field Interaction Research Articles

Magnetic field-induced asymmetric mechanical metamaterials

We propose a magnetic field-induced asymmetric mechanical metamaterial. The tunable metamaterial integrates hard-Magnetic Active Elastomers (hMAEs) into the microstructural design combining snap-through, bi-stability, and local resonant effects. The proposed metamaterial design comprises resonating units made out of hMAE, and these units are supported by highly deformable curved beams connected with an elastomeric matrix. Activated by a magnetic field, the resonating units attain an unstable regime with dramatic configuration and stiffness variation. These controlled transformations significantly affect the elastic wave propagation. We illustrate that the proposed magnetoactive metamaterial enables bandgap tunability over a broadband low-frequency range. Thus, the proposed design allows remote and reversible control of the metamaterial performance. Moreover, the hMAE-based systems can incorporate the polarity and chirality stemming from the interaction of external magnetic fields and hMAE phases, giving rise to the unusual behavior of the metamaterial, and potentially enabling elastic cloaking.

Notch tensile properties of Magnetically Impelled Arc Butt (MIAB) welded T11 steel tubes

The Magnetically Impelled Arc Butt (MIAB) welding process uses a rotating arc as its heat source and is known as an efficient method for tube welding. Interaction of external magnetic field and induced magnetic flux results in the creation of Lorentz force along peripheral edges of tubes. The circumferential arc rotation helps in the uniform heating of faying surfaces. After sufficient melting, faying surfaces are pressed against each other for weld formation. This paper aims at studying the notch tensile properties of T11 tubes welded by MIAB welding. In MIAB welded T11 steel tubes various Thermo-Mechanically Affected Zones (TMAZ) are formed as an effect of heat and pressure during welding. Tensile properties of all these TMAZs are different due to varying microstructures. Therefore notched tension testing was carried out to compare the properties of various zones in welded T11 tubes. All TMAZs show higher notch ductility with Notch Strength Ratio (NSR) greater than one. In comparison to the base metal, all TMAZs except TMAZ III display no loss in notch strength. The presence of granular bainite in TMAZ III causes lower notch strength with a Normalized Notch strength (NTSN) ratio less than unity.

Thermomagnetic characterization of Ising-type ferromagnets of spins S=5/2 and σ=7/2: a Monte Carlo study

In this investigation through of Monte Carlo simulations we characterize thermomagnetically two Ising type ferromagnetic models of spins S = ±5/2, ±3/2, ±1/2 and σ = ±7/2, ±5/2, ±3/2, ±1/2 located alternately in a square lattice, formed by two sublattices A and B each with 120 sites containing the spins S and σ, respectively. The ferromagnetic configurations studied are defined by and H1 and H2 Hamiltonians with next neighbors and next nearest neighbors exchange interactions, and single ion anisotropy and external magnetic field interactions. The thermomagnetic analysis of the system defined by H1 Hamiltonian shows discontinuities in the magnetization, as well as a strong influence of magnetic field on the critical and discontinuous transition temperatures. For the case of the ferromagnet defined by H2 Hamiltonian, after analyzing the effects of the next nearest neighbors interactions and magnetic field, we find an almost linear dependence on the critical temperature. The study of hysteresis behavior in both ferromagnets shows the phenomenon of exchange bias.

MHD effect under the interaction of external magnetic field with electrolytic hydrogen and oxygen bubbles

MHD effect under the interaction of external magnetic field with electrolytic hydrogen and oxygen bubbles

Generation of Au nanorods by laser ablation in liquid and their further elongation in external magnetic field

Laser-assisted single-step generation of elongated Au NPs is reported. Laser-generated Au NPs have some fraction of spherical NPs and elongated NPs with aspect ratio of 6–8. The behavior of these NPs in a permanent magnetic field up to 7 Tesla is experimentally studied using in-situ optical absorption spectrometry. It is found that magnetic field causes irreversible changes in the aspect ratio of elongated Au NPs. Residence in magnetic field for time of order of tens minutes is accompanied by further elongation of Au NPs and formation of Au nanowires with aspect ratios up to 17–18. This is corroborated with TEM images of Au NPs before and after the action of magnetic field. The results are interpreted on the basis of interaction of external magnetic field with that of electrons that take part in longitudinal plasmon oscillations in elongated Au NPs.

Monte Carlo study of the magnetization reversal times in a core/shell magnetic nanoparticle

In this work, we present an investigation of the magnetization reversal times for a ferromagnetic/antiferromagnetic core/shell nanoparticle, by means of Monte Carlo simulations. The magnetic behavior of the nanoparticle was evaluated with a classical Heisenberg Hamiltonian, which includes terms for the exchange interaction, external magnetic field interaction and uniaxial anisotropy. We determined the magnetization reversal times for the core and core interface, when the system is initially ordered and it is subjected to a negative magnetic field. We computed the influence of the core/shell exchange interaction, as well as the core anisotropy, core size and temperature dependence on the reversal times. It was found that there exists a strong influence of core/shell exchange interaction on the core sites reversal time. These parameters influence the reversal time in different ways. In general, the increment of the temperature and the core/shell exchange interaction produce a faster magnetization reversal. Moreover, the core interface reverses faster than the core bulk. On the other hand, the reversal time depends on the anisotropy and the uncompensated sites in the shell interface. In this way, it is possible to control the core reversal time in these kind of nanoparticles by means of the core/shell interface.

Reentrant and spin compensation phenomena in an Ising type ferrimagnetic system

A mixed spin-1 and spin-2 Ising ferrimagnetic system is investigated on a square lattice of spins S=±2,±1,0 and Q=±1,0 in the presence of an h′ external magnetic field, such that S and Q are nearest-neighbors antiferromagnetically coupled. Using Monte Carlo simulations we calculate the finite temperature phase diagrams of the magnetization and the specific heat. We consider ferromagnetic interactions between next-nearest neighbors, S spins (J2′), as well as between the Q spins (J3′), and crystal field and external magnetic field interactions at each point of the lattice. Under these conditions the system exhibits spin compensation temperatures and a first-order reentrant behavior in a certain range of the parameters of the Hamiltonian. We analyze the behavior of the critical and compensation temperatures, as well as the first order phase transition temperatures, with the external magnetic and crystal fields, and the next-nearest neighbors interaction between S spins. We found that the existence of compensation temperatures and a first order phase transition depends on the strength of h′, J2′ and D′.

Evidence for the ferromagnetic frustration in a classical spin-[formula omitted] system with multisite interaction in external magnetic field: Exact results

We investigate the influence of the multisite interaction among sites within elementary triangles of the kagome-like recursive lattice on the properties of the classical spin-1∕2 ferromagnetic Ising model in the external magnetic field. The exact solution of the model is found and it is shown that the model exhibits a nontrivial structure of the first order as well as second order phase transitions in nonzero external magnetic fields related to the multisite interaction. The equation for the exact determination of the positions of the critical points of the second order phase transitions is derived. The thermodynamic properties of the model are investigated in detail and it is shown that the competition between the ferromagnetic interaction and the multisite interaction leads to the appearance of strong ferromagnetic frustration effects represented by the formation of a nontrivial system of macroscopically degenerated plateau-like and single-point-like ground states. The residual entropies of all ground states are found and the kagome spin-ice-like highly macroscopically degenerated plateau state with nonzero magnetization is identified with the exact residual entropy per site s∕kB=ln(4∕3)∕3≈0.095894. The properties of the specific heat are investigated, its Schottky-type behavior near the single-point ground state values of the magnetic field is identified, the existence of large magnetocaloric effect is discussed, and the existence of the first order phase transitions without the specific heat capacity change is demonstrated.

Vectorized magnetometer for space applications using electrical readout of atomic scale defects in silicon carbide

Magnetometers are essential for scientific investigation of planetary bodies and are therefore ubiquitous on missions in space. Fluxgate and optically pumped atomic gas based magnetometers are typically flown because of their proven performance, reliability, and ability to adhere to the strict requirements associated with space missions. However, their complexity, size, and cost prevent their applicability in smaller missions involving cubesats. Conventional solid-state based magnetometers pose a viable solution, though many are prone to radiation damage and plagued with temperature instabilities. In this work, we report on the development of a new self-calibrating, solid-state based magnetometer which measures magnetic field induced changes in current within a SiC pn junction caused by the interaction of external magnetic fields with the atomic scale defects intrinsic to the semiconductor. Unlike heritage designs, the magnetometer does not require inductive sensing elements, high frequency radio, and/or optical circuitry and can be made significantly more compact and lightweight, thus enabling missions leveraging swarms of cubesats capable of science returns not possible with a single large-scale satellite. Additionally, the robustness of the SiC semiconductor allows for operation in extreme conditions such as the hot Venusian surface and the high radiation environment of the Jovian system.

Backward flowing molten metal in weld pool and its influence on humping bead in high-speed GMAW

The additional electromagnetic force generated by the interaction of external magnetic field and the welding current was applied to suppress the momentum of the backward flowing metal and to prevent the occurrence of humping bead in high speed gas metal arc welding. The vision-based observation was utilized to capture the images of the weld pool and the features of the backward flowing molten metal in the weld pool were extracted and compared under different welding speeds and excitation currents of the magnetic field. The velocity of the backward molten metal flow on the surface of the weld pool was calculated and analyzed by the combination of the visual observation and the tracer particle technique. It was found that the velocity of the backward flow metal are decreased and the humping was disappeared when the external magnetic field was applied.

Unexpected transitions induced by spin-dependent, hyperfine and external magnetic-field interactions

Unexpected transitions are induced by weaker interactions not included in the gross structure model of the ion under investigation. We discuss different examples of such decay channels, starting with relativistic spin-induced transitions. These represented an important field of study a few decades ago, and we illustrate how some challenging cases can be treated very accurately with todayʼs computational techniques, while close degeneracy sometimes still prevents ab initio methods from obtaining accurate results. For hyperfine induced transitions we review some recent results and discuss remaining challenges for experiment and theory. Finally, we discuss the newly opened field of accurate calculations for transitions induced by an external magnetic field and point to some examples of where these are accessible for experimental tests.

Collision of two atoms in laser radiation field with formation of Feshbach resonances

Based on the simplest two-channel model we theoretically consider laser induced elastic and inelastic collision of two atoms with formation of Feshbach resonance. In cases of one- and two-photon resonances of laser radiation with two discrete vibrational molecular levels, we show that Feshbach resonances appear at interaction of external magnetic field with dressed states formed via Autler-Townes effect. We also study the laser-induced inelastic collision and its influence on the considered processes. In case of two-photon resonance between discrete vibrational molecular states the Feshbach resonances arise under action of magnetic field via Autler-Townes effect, while the laser-induced transition into the elastic-channel continuum is in this case absent. We obtain the cross-sections of elastic and inelastic scattering and show that quenching of resonance occurs under certain conditions. The obtained results can be employed in new studies of collisions of atoms, e.g., of alkali metal atoms, and for interpretation of new experiments in BECs.

Thermal entangled quantum Otto engine based on the two qubits Heisenberg model with Dzyaloshinskii–Moriya interaction in an external magnetic field

Based on the isotropic two spin-1/2 qubits Heisenberg model with Dzyaloshinskii–Moriya interaction in a constant external magnetic field, we have constructed the entangled quantum Otto engine. Expressions for the basic thermodynamic quantities, i.e. the amount of heat exchange, the net work output and the efficiency, are derived. The influence of thermal entanglement on these basic thermodynamic quantities is investigated. Moreover, some intriguing features and their qualitative explanations in zero and finite magnetic field are given. The validity of the second law of thermodynamics is confirmed in the system. The results obtained here have general significance and will be useful in increasing understanding of the performance of an entangled quantum engine.

Hopping transport in two-dimensional systems with spin-orbit interaction in external magnetic field

The theory of spin rotation waves (SRWs), representing excitations of a new type arising in twodimensional systems with spin-orbit interaction in an external electric field, has been developed. These intrinsic modes correspond to rotation of the magnetic moment vector in the plane formed by the electric field vector and the normal to the sample plate surface. An experimental method is proposed for detecting SRWs by measuring the frequency dependence of the magnetic susceptibility, which exhibits a resonance at the intrinsic mode frequency. A particular calculation is performed for a hopping conductivity model (for small-size polarons), but it is likely that intrinsic oscillations of the SRW type also take place for the band transport, since their appearance is related to the symmetry of the system.

バルク高温超伝導体開発の現状

Recent advancement in materials processing enabled us to grow large single-grain bulk RE-Ba-Cu-O superconductors (RE: rare earth elements) with high critical current densities. These superconductors can exhibit a large electromagnetic force with the interaction of external magnetic fields. Various devices have been developed by utilizing such a force: magnetic bearings, flywheels for energy storage, load transport, hysteresis motors, and several levitation devices. A large magnetic field can also be trapped by bulk superconductors, which can function as a quasipermanent magnet. Trapped field values have already reached 10T, thus leading to many novel applications of high trapped field magnets. The final target will be a second-generation Maglev train.

Magnetically Tailored Arc and Glow Discharge Plasmas for Atomic Spectroscopy

Three magnetic field-plasma configurations are used to study the interaction of external magnetic fields with analytically useful plasma devices. First, a magnetic field oscillating at 60 Hz and normal to the electric field in a 12-A direct current arc plasma is used to obtain an Ē×B̄ drift motion of the arc current channel. This causes a periodic vertical displacement of the channel. Second, a cw magnetic field is used to alter the structure and radiative properties of a demountable glow discharge lamp that uses a center-post cathode. The magnetic field axis is parallel to the cathode axis, and the lamp is operated in a pseudo-magnetron mode. Third, a damped, oscillatory magnetic field produced by discharging a capacitor through a coil is used to alter the radiative characteristics of several commercial hollow cathode lamps. The magnetic field is parallel to the cathode axis, and again the lamps operate in a pseudo-magnetron mode. In all three systems, the presence of the magnetic field drastically alters the radiative properties of the plasmas.

Magnetically Tailored, Atmospheric-Pressure Plasmas for Atomic Spectroscopy

Three magnetic field-plasma configurations are used to study the interaction of external magnetic fields with analytically useful, atmospheric-pressure plasmas. A magnetic field normal to the electric field in the plasma produced by the capacitive discharge vaporization of a thin Ag film is used to obtain an ExB drift motion of the plasma. Photographs show that this drift motion can drastically alter the size, shape, and location of the plasma. The same plasma-generation technique is combined with a nonuniform magnetic field to obtain an adiabatic magnetic-mirror ion trap. Finally, the cylindrically symmetric plasma produced by the capacitive discharge vaporization of a thin metal wire or a bundle of graphite fibers is combined with an axial magnetic field to obtain a theta pinch of the plasma. In all cases, the plasma current is used to generate the magnetic field in a large air-core inductor surrounding the plasma. Radiative and electrical properties of these magnetically modified plasmas will be presented.

Effect of Electron Spin Paramagnetism on the Velocity of Sound in Metals

Increase of sound velocity in metals due to external magnetic field interaction with magnetic moment of conduction electrons