Influence Of High Magnetic Field Research Articles

A study on the magnetothermal properties and magnetocaloric effect in [formula omitted] ([formula omitted

In this study, we investigate the Gd1−xCexMn2Ge2 system with x=0.17 and x=0.33 using the mean field theory. Ab-initio based calculations are used to determine the density of states at Fermi energy, D(Ef), and Debye temperature θD for GdMn2Ge2 main compound. Our aim is to determine key properties such as magnetization, magnetic heat capacity, and the magnetocaloric effect main aspects including both isothermal entropy change and adiabatic temperature change. We examine these parameters under various conditions by applying different field changes up to 6 T and at temperatures spanning a range up to 400 K. The two systems have a Curie temperature, that is around room temperature (around 330 K). Using the trapezoidal method, the Gd1−xCexMn2Ge2 systems exhibit a maximum ΔSm value of 0.79 J/mol K for ΔH=6 T, and a ΔT value of an average 1.3 K/Tesla. In our study, the relative cooling power (RCP) was investigated and moreover, we examined the nature of phase transitions using universal curves and Arrott plots to confirm that the nature of phase transition at Tc in this system corresponds to a second-order phase transition (SOPT). The influence of high magnetic fields on the magnetization was also examined, and it showed first-order phase transition (FOPT) at low temperatures and high fields. Additionally, due to FOPT, a change in magnetic order from ferrimagnetism to ferromagnetism took place.

Controversies about hydrogen bonds in water molecules on the influence of high magnetic fields: implications on structural and electronic parameters

ABSTRACT The application of a magnetic field in water has been the subject of discussion because of possible technological innovations and controversies. Herein, theoretical calculations were carried out and a high magnetic field was applied in different directions, senses and intensity in water dimers. Our findings point out that these three variables significantly impact the obtained trend and results considering the hydrogen bond strength. Keeping this in mind, a better description of the experimental arrangement should occur to inform the positioning of the field in relation to the system to avoid controversies, especially in fields smaller than 100 T.

Revealing the influence of high magnetic field on the solute distribution during directional solidification of Al-Cu alloy

The effect of the high magnetic field (MF) on the distribution of solute concentration during directional solidification of Al-Cu alloy under low growth speed was experimentally investigated. The amount of non-equilibrium eutectic is quantified via X-ray computed tomography (XCT) and demonstrated to reduce with the application of MF. Further, experimental results reveal that the MF alleviates the microsegregation and increases the average Cu concentration in solid solution, leading to the increases of the effective partition coefficient ke. It was also found that Cu concentration in solid solution increases continuously with the increasing intensity of MF, following the strengthening of micro-hardness. The change of ke under the MF is demonstrated to attribute to the thermoelectric magnetic convection (TEMC) in the mushy zone and the thermoelectric magnetic force (TEMF) acting on the solid. The TEMC is supposed to cause secondary convection owing to the inequality in flow velocities of circulation in different positions of dendrite stem. And the vacancies created by the proliferation and movement of dislocations induced by TEMF in the matrix is supposed to be able to capture solute atoms and thus enhance the solute concentration in the solid solution.

A novel strategy for hierarchical structure in multicomponent nano-precipitated steels by high magnetic field aging

The influence of high magnetic field (HMF) during aging on the precipitation behavior of co-precipitates consisted of Cu-rich precipitates and Ni(AlMn) precipitates in multicomponent nano-precipitated steels was carefully investigated. It was indicated that HMF promoted the construction of hierarchical structures of Cu-rich and Ni(AlMn) co-precipitates. It was thought that HMF increased nucleation rates of secondary co-precipitates during aging because of the thermodynamics change, thus refining the secondary precipitates. Meanwhile, HMF increased the Ostwald ripening rate of primary particles during the further aging after tempering because of increasing diffusion of Cu, thus accelerating the coarsening process.

Influence of high magnetic field on the liquid-liquid phase separation behavior of an undercooled Cu–Co immiscible alloy

Abstract In this work, the influence of 10 T high magnetic field on the liquid-liquid phase separation behavior of Cu-33.33 at.%Co immiscible alloy was systematically investigated. The results show that the separation behavior was significantly altered via the application of a high magnetic field. Both the Co-rich phase and the non-ferromagnetic Cu-rich phase are found to be elongated along the magnetic field direction due to the action of static magnetic energy and the coordinating of deformation. The relatively homogeneous microstructure of uniform dispersion of Co-rich phase on the matrix is obtained in the direction perpendicular to the magnetic field. The drag force induced by the thermoelectric magnetic convection under a high magnetic field hinders the solute transport of Co-rich phase, leading to a decline in the number of Cu-rich phase produced by the secondary decomposition. Moreover, the applied high magnetic field results in the variations of the undercooling during rapid solidification. The finally solidified Cu–Co alloy in a magnetic field of 10 T with higher undercooling exhibited a slightly lower saturation magnetization and higher coercivity and residual magnetizations. The present research provides new insights into the influence of high magnetic field on the liquid-liquid phase separation behavior of immiscible alloys.

Structural, ferromagnetic, and optical properties of Fe and Al co-doped ZnO diluted magnetic semiconductor nanoparticles synthesized under high magnetic field

In this study, 2% Fe and 3% Al co-doped ZnO nanoparticles were synthesized using a hydrothermal method under high magnetic field (HMF). The influences of HMF on the structural, optical, and ferromagnetic properties of Fe and Al co-doped ZnO nanoparticles were characterized and analyzed. The single-phase wurtzite structure of the synthesized samples was confirmed using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy analysis. The application of HMF decreases the particle size of the spherical nanocrystal as observed by scanning electron microscopy (SEM). Optical analysis indicated that the absorption edge shifted towards a higher wavelength (red shift). The nanoparticles synthesized under the HMF exhibited high room temperature ferromagnetism (RTFM) performance because of the high oxygen vacancy (VO) content as revealed by X-ray photoelectron spectroscopy (XPS), which was in agreement with the prediction of the bound magnetic polarons theory.

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.

Magnetoresistance of (Co40Fe40B20)x(SiO2)100−x and (Co84Nb14Ta2)x(Al2O3)100−x nanocomposites below the percolation threshold in pulsed magnetic fields

We present results of experimental studies of magnetic properties, resistivity and magnetoresistance (MR) focusing on MR in high magnetic fields of (Co40Fe40B20)x(SiO2)100−x and (Co84Nb14Ta2)x(Al2O3)100−x nanocomposites near the percolation threshold. The nanocomposite films with x = 47–58 at.% were deposited onto a glass-ceramic substrate by the ion-beam sputtering. The samples consist of metallic nanogranules embedded into the nonstoichiometric matrix. According to the structural and magnetic data a large amount of metallic atoms are dispersed between magnetic nanogranules. With decreasing metal volume fraction the temperature dependence of conductivity changes from lnT behavior, matches a strong tunnel coupling between nanogranules, to the T1/2 dependence below the metal-insulator transition. MR was studied in pulsed magnetic fields up to 20 T at T = 65–300 K. The pulse duration was 11 ms. Negative MR almost saturates with increasing magnetic field but slowly increases or decreases in high magnetic fields. There is an evidence of linear positive contribution to MR above saturation at 65–300 K with the slope (3–9) 10−3% T−1. It was shown that possible reason for positive MR is influence of high magnetic field on the tunnel barrier height and as a result on the tunnel transparency.

Spinodal Decomposition in Fe-25Cr-12Co Alloys under the Influence of High Magnetic Field and the Effect of Grain Boundary.

Fe-Cr-Co alloys precipitate nanosized α1 particles through spinodal decomposition, and their magnetic performance is susceptible to influence by the shape and arrangement of α1 particles. We studied spinodal decomposition during the heat treatment of Fe-Cr-Co alloys by both experimental and numerical simulation. Fe-Cr-Co alloys were fabricated first by directional solidification, followed by thermomagnetic treatment in a high magnetic field (HMF) and step aging. The experimental results show a spinodally decomposed structure consisting of nanosized α1 particles. The applied HMF caused the α1 phase to change into a rod-like shape. Moreover, a feather-like structure was observed near the grain boundary (GB), with slim α1 rods regularly arranged along the direction perpendicular to the GB. With the shape change and alignment of the α1 phase in the HMF, Fe-Cr-Co alloys show magnetic coercivity that is superior to those of samples without an HMF. To reveal the influence of HMF on phase transformations and the effect of GB, we conducted phase-field simulations of spinodal decomposition in the Fe-Cr-Co alloy. A migrating GB contributes to the elongation and arrangement of the α1 phase in the regions where the GB has passed. Thus, the α1 phase is arranged as parallel rods that are perpendicular to the GB. This GB effect consists of the effect of enhanced atomic mobility and the elastic energy. The α1 rods are elongated along the direction of HMF. The simulation results indicate that the feather-like structure is caused by a combined effect of both the GB and HMF. It is shown that the model generates microstructures which are qualitatively similar to those observed experimentally.

Influence of high magnetic field on access to stationary H-modes and pedestal characteristics in Alcator C-Mod

Recent Alcator C-Mod experiments have explored access to and characteristics of H-modes at magnetic fields approaching 8 T, the highest field achieved to date in a diverted tokamak. The H-modes originated from L-mode densities ranging from to , allowing insight into the density dependence of the H-mode power threshold at high magnetic field. This dependence is compared to predictions from the ITPA scaling law ([]), finding that the law is approximately accurate at 7.8 T. However, the law underpredicted the high density H-mode threshold at lower magnetic field in previous C-Mod experiments ([]), suggesting that the overall dependence of the threshold on magnetic field is weaker than predicted by the scaling law. The threshold data at 7.8 T also indicates that the onset of a low density branch at this magnetic field on C-Mod occurs below , which is lower than predicted by an existing model for low density branch onset. The H-modes achieved steady-state densities ranging from to , and higher transient densities, and had values of q95 from 3.3 to 6.0. This parameter range allowed the achievement of all three types of H-mode routinely observed at lower magnetic field on C-Mod: the stationary, ELM-suppressed Enhanced Dα (EDA) regime, seen at high densities and high values of q95; the nonstationary ELM-free regime, seen at lower densities and values of q95; and the ELMy regime, seen at low density, moderate q95, and specialized plasma shape. The parameter space in which these regimes occur at 7.8 T is consistent with lower magnetic field experience. Pressure pedestal height at 7.8 T is compared to EPED [, ] predictions, and a scaling law for EDA density pedestal height developed between 4.5 T and 6.0 T is updated to include fields from 2.7 T to 7.8 T. Overall, this analysis increases confidence in the use of low magnetic field experience to predict some elements of high magnetic field tokamak behavior.

High Magnetic Field-Induced Formation of Banded Microstructures in Lamellar Eutectic Alloys During Directional Solidification

The influences of high magnetic field (up to 12 T) on the morphology of Pb-Sn and Al-Al2Cu lamellar eutectics during directional solidification were investigated. The experimental results indicate that, along with a decrease in eutectic spacing, the banded structure forms at lower growth speeds under high magnetic field and the band spacing decreases as the magnetic field increases. Moreover, the application of a magnetic field enriches the Cu solute in the liquid ahead of the liquid/solid interface during directional solidification of an Al-Al2Cu eutectic alloy. The effects of high magnetic field on the eutectic points of non-ferromagnetic alloys and the stress acting on the eutectic lamellae during directional solidification have been studied. Both thermodynamic evaluation and DTA measurements reveal that the high magnetic field has a negligible effect on the eutectic points of non-ferromagnetic alloys. However, the high magnetic field caused an increase of the nucleation temperature and undercooling. The numerical results indicate that a considerable stress is produced on the eutectic lamellae during directional solidification under high magnetic field. The formation of a banded structure in a lamellar eutectic during directional solidification under high magnetic field may be attributed to both the buildup of the solute in the liquid ahead of the liquid/solid interface and the stress acting on the eutectic lamellae.

Magneto-heat capacity study on Kondo lattice system Ce(Ni 1−x Cu x )2Al3

Heat capacity studies on the Kondo lattice system Ce(Ni1−x Cu x )2Al3, in the presence of magnetic fields, were reported for x = 0.0−0.4. The physical properties of the intermediate compositions like x = 0.3 and 0.4 were known for their enhanced thermoelectric power and hence have been analysed with an extra interest. It was also shown from the X-ray diffraction that these systems with x = 0.3 and 0.4 were in single phase in terms of sample purity and it stabilized the phases easily with the increase in the Cu doping in the system. The low temperature rise in C p/T below 10 K under the influence of high magnetic fields was analysed using a multi-level Schottky effect. A gradual decrease of the total angular momentum (J) with the increase of applied magnetic fields indicated a scenario of screening of Ce3+ magnetic moment while simultaneously the system settled for the Fermi liquid state. The screening thus seen was in line with the expectations of electrical conductivity measurements on these samples.

Effects of High Magnetic Field Postannealing on Microstructure and Properties of Pulse Electrodeposited Co-Ni-P Films

The influence of high magnetic field annealing on the morphology, microstructure, and properties of pulsed-electrodeposited Co-Ni-P films was investigated. The as-deposited film with a rough surface changed into uniform nanocrystalline during the magnetic field annealing process. In particular, the formation of intestine-like appearance with spherical clusters vanishing is favored from a moderate magnetic field strength of 6 T, due to the polarized effects. Meantime, the diffraction peak (111) of α (fcc) phase shifts to the right direction, which is attributed to the fact that more Co atoms from phosphide phase are incorporated into the Ni lattice, in comparison with the case of annealing under 0 T and 12 T magnetic fields. The mechanical and magnetic properties of the films reach relative optimum values at B=6 T. The evolution of magneto-induced modification in the Co-Ni-P morphology, structure, and properties can be explained by the polarized effect and the diffusion-acceleration effect under a high magnetic field.

Microstructural evolution and magnetic properties of nanocrystalline Fe films prepared in a high magnetic field

In this study we have explored how a high magnetic field (HMF) affects the structure and magnetic properties of Fe thin films fabricated on Si (100) substrates at various substrate temperatures by using a thermal evaporation method. At a substrate temperature of room temperature (RT), the HMF increased the width of column and the formation energy of the films. This behavior occurred because the HMF induced an excess energy-Zeeman energy which is larger than the sum of the kinetic energy and thermal energy of Fe without the HMF. This increased the particle size and decreased the roughness of the film deposited at RT and 6 T. When the substrate temperature was increased to 400 °C, the growth mode is changed from columnar (RT) to layered (400 °C). The HMF increased the grain size. The film deposited at RT and 6 T had much improved soft magnetic properties from its modified microstructure. While thermal disturbances decreased the effect of HMF on the magnetic properties of the film deposited at 400 °C. In particular, the influence of HMF on the microstructure and magnetic properties of Fe films is significant not in the evaporation stage but in the condensation process of film.

Magneto-transport properties of poly-silicon in SOI structures at low temperatures

Silicon-on-insulator structures are an important material for modern microelectronic devices, in particular, for sensors of various physical values. As the electro-transport properties of such initially polycrystalline dispersed structures vary with the treatment of poly-silicon layer, this will determine, in particular, the device implementation of SOI at low temperatures. In this paper we report on extended AC and DC studies of low-temperature electrical conductivity of SOI-structures with initial boron concentrations in the vicinity to metal–insulator transition (2.4×1018сm−3 and 4.8×1018сm−3 for non-recrystallized and recrystallized samples, respectively) and its peculiarities at the influence of high magnetic fields. In particular, together with the results of DC studies of resistivity the observation of negative magnetoresistance at low magnetic fields imply the hopping conductivity of poly-silicon layers at low temperatures (lnρ~Т−1/4). The study of the properties of poly-silicon layers in SOI structures by impedance analysis method (AC measurements) allowed for determining the effect of material dispersion on its low-temperature conductivity and for separating and identifying the contributions of various microstructure elements in the sample conductivity. In both the DC and AC cases the Mott law hopping conductivity in non-recrystallized poly-Si samples has been confirmed at cryogenic temperatures around liquid helium point. A capacitive type of Nyquist plot in turn supported this assumption. In laser-recrystallized poly-Si layers the charge carrier transport is limited by grain barriers and corresponds rather to percolation type of conduction, obeying the Shklovskii–Efros law.

Influence of high magnetic field on the luminescence of Eu3+-doped glass ceramics

Rare earth (RE) doped materials have been widely exploited as the intriguing electronic configuration of RE ions offers diverse functionalities from optics to magnetism. However, the coupling of magnetism with photoluminescence (PL) in such materials has been rarely reported in spite of its fundamental significance. In the present paper, the effect of high pulsed magnetic field on the photoluminescence intensity of Eu3+-doped nano-glass-ceramics has been investigated. In our experiment, Eu-doped oxyfluoride glass and glass ceramic were prepared by the conventional melt-quenching process and controlled heat treatment. The results demonstrate that the integrated PL intensity of Eu3+ decreases with the enhancement of magnetic field, which can be interpreted in terms of cooperation effect of Zeeman splitting and magnetic field induced change in site symmetry. Furthermore, as a result of Zeeman splitting, both blue and red shift in the emission peaks of Eu3+ can be observed, and this effect becomes more prominent with the increase of magnetic field. Possible mechanisms associated with the observed magneto-optical behaviors are suggested. The results of the present paper may open a new gate for modulation of luminescence by magnetic field and remote optical detection of magnetic field.

Suppression of decoherence in a graphene monolayer ring

The influence of high magnetic fields on coherent transport is investigated. A monolayer graphene quantum ring is fabricated and the Aharonov-Bohm effect is observed. For increased magnitude of the magnetic field, higher harmonics appear. This phenomenon is attributed to an increase of the phase coherence length due to reduction of spin flip scattering.

Effect of tempering temperature on carbide precipitation behaviours in high strength low alloy steel under high magnetic field

The influence of high magnetic field on carbide precipitation behaviours during the tempering of a high strength low alloy steel was investigated by means of transmission electron microscopy. TEM analysis results indicated that the applied high field effectively promoted the precipitation of Fe5C2 type carbide at low temperature (200°C) and the precipitation of M6C type carbide at intermediate temperature (530°C). The promotion of specific carbides at low and intermediate temperature was caused by the reduction in magnetic Gibbs free energy. Regarding the magnetic Gibbs free energy of carbides, not only the magnetization but also the internal field induction related to the morphology of carbide was taken into consideration. It was observed that there was no pronounced effect of high magnetic field on the precipitation sequence of alloy carbides when specimens were tempered at 700°C, because they were changed into paramagnetic phases at this temperature.

Influence of High Magnetic Field on β-a Phase Transformation in TC4 Titanium Alloy

In the TC4 titanium alloy subject to high pulsed magnetic field, the phase transformation from α to β occurs. When the magnetic induced intensity increased from 2T, 3T to 4T with constant 30 pulses, the percent of α phase adds up gradually. When the magnetic induced intensity is 4T the volume fraction of α phase amounts up to 59%. It is ascertained that magnetic field has taken a positive influence on the phase transformation because of the variation of inner energy induced by magnetic field.

Effects of high magnetic field on isothermal pearlite transformation and microstructure in a hypereutectoid steel

A high magnetic field was applied during the isothermal pearlite transformation of a hypereutectoid carbon steel at three different temperatures. It was found that the magnetic field applied can increase the transformation rate and the pearlite nodule growth rate, decrease the interlamellar spacing of pearlite and the amount of low angle boundary in ferrite lamella. The magnetic field effects are more obvious at high temperature. The mechanism of field-effect was discussed by analyzing the influences of high magnetic field on the eutectoid temperature, diffusion activation energy in austenite, Gibbs free energy of ferrite and dislocation mobility.