Effect Of High Magnetic Field Research Articles

Magnetic Field-Induced Precipitation Behaviors of Alloy Carbides M2C, M3C, and M6C in a Molybdenum-Containing Steel

The effect of a 12-T high magnetic field on alloy carbide precipitation in an Fe-C-Mo alloy during tempering at an intermediate temperature was investigated. Thin foils and carbon extraction replicas of the treated specimens were examined by transmission electron microscopy (TEM). The results show that the applied high field effectively promoted the precipitation of (Fe,Mo)6C alloy carbide. The concentration of Fe atom in Fe6−xMoxC carbide is increased whereas that of Mo atom decreased when the high magnetic field was applied. However, the high magnetic field almost had no detectable influence on the atom concentration in (Fe,Mo)2C and (Fe,Mo)3C carbides. First principle calculations have been performed to calculate the magnetic moment per iron atom of the carbides to explore the origin of the effect of the magnetic field. The influence of the high magnetic field on the precipitation behaviors of alloy carbides was closely related to the magnetic moment of (Fe,Mo)2C, (Fe,Mo)3C, and (Fe,Mo)6C. The magnetic field promotes the formation of the carbides with high total magnetic moment. The effect of the high magnetic field on the substitutional solute atom (Fe and Mo) concentration change in the three alloy carbides was attributed to their magnetization differences per Fe atom.

Effects of high magnetic field on structure and optical properties of metal ions doped modified CaTiO3

In the paper, the changes of structures and optical properties of metal ions doped modified CaTiO3 prepared under different magnetic field intensities (up to 12 T) and 800 ℃ are studied. The results indicate that the photo absorption performances are enhanced with the ions doped concentration increasing and red shift occurs significantly. With the same doped concentration, the photo absorption performances of the samples prepared under magnetic field are improved compared with under no magnetic field, while there are little differences among the absorption curves of these samples prepared under different magnetic field intensities. Furthermore, it is observed that the X-ray diffraction curve peaks of pure CaTiO3 prepared under magnetic field are all left-shifted and cutoff wavelengths of UV-vis are augmented, which indicates that the interplanar spacing and lattice constant are increased while the band gap is narrowed.

Progress on High Magnetic Field-Controlled Transport Phenomena and Their Effects on Solidification Microstructure

The recent contributions on changes induced by high magnetic fields in transport phenomena, such as convection, solute diffusion, solute or phase migration in the liquid, are reviewed and analyzed. Selectivity provided by the Lorentz, thermoelectromagnetic (a special kind of Lorentz force), and magnetic forces or combinations enables the control of transport phenomena in liquids. This possibility, together with the capability of the transport phenomena to affect solidification in alloys, allows a level of control over solidification microstructures. As a result, recent relevant work can be found dealing with the effects of high magnetic fields on transport phenomena and the corresponding solidification microstructure evolution of alloys, based on the Lorentz, thermoelectromagnetic, and magnetic forces or combinations thereof.

Effect of weak and high magnetic fields in longitudinal and transverse configurations on magneto-thermoelectric properties of quantum Bi wires

We report on the magneto-thermopower of single-crystal Bi nanowires with diameters 75 and 250 nm in a longitudinal and transverse magnetic fields of 0–14 T. The temperature range is 1.5–300 K. Bi nanowires in a glass capillary have been prepared by the high frequency liquid phase casting. The temperature dependence R(T) shows the transition from metallic to semiconducting behavior due to quantum size effect, where the Bi-wire diameter is reduced to less than 80 nm. It is for the first time that the effect of the negative magneto-resistance in a transverse magnetic field, due to the quantum size effect on 75 nm Bi wires, has been observed. The thermopower is very sensitive to the wire diameter, up to a change in the sign from negative to positive at low temperatures, and to a significant extent in a weak longitudinal magnetic field. The field dependences of longitudinal and transverse magneto-resistance have features characteristic of the occurrence of the quantum size effect and galvanomagnetic size effect, and provide information on the parameters of the energy spectrum and charge carrier mobility. The enhancement of the thermoelectric figure of merit for Bi nanowires is discussed. We also discuss the power factor α2σ and its dependence on the diameter, magnetic field and temperature.

Effects of high magnetic fields on the crystal orientation and magnetostriction of a TbFe2 based alloy during treatment in the semi-solid state

A TbFe2 based alloy was treated in the semi-solid state under high magnetic fields of 0T, 4.4T, 8.8T and 11.5T. The effects of high magnetic fields on crystal orientation, magnetization and magnetostriction of the alloys were investigated. We found that with an increase in the magnetic flux density from 0T to 11.5T the orientation of the TbFe2 phase experienced a transformation from 〈113〉 to 〈111〉 to 〈110〉. The alloy treated at 8.8T showed magnetic anisotropic behavior, while the alloys treated at 0T, 4.4T and 11.5T showed magnetic isotropic behavior. Compared with the alloy treated at 0T, the magnetostrictive property was slightly lower at 4.4T, but significantly higher at 8.8T and 11.5T. The change in magnetostrictive property comes from the evolution of TbFe2 crystal orientation.

Effect of an axial high magnetic field on Sn dendrite morphology of Pb–Sn alloys during directional solidification

The influence of an axial high magnetic field (up to 12 T) on Sn dendrite morphology in directionally solidified Pb–Sn alloys has been investigated experimentally. Results show that the magnetic field has modified the Sn-dendrite morphology dramatically. Indeed, it has been found that the applied magnetic field has destroyed the Sn-dendrite array and caused the occurrence of the columnar-to-equiaxed transition (CET) at lower growth speeds (R<20μm/s). Along with the occurrence of the CET, equiaxed grains are aligned under the magnetic field. The effect of the magnetic field weakens as the growth speed increases. Further, the amplitude and distribution of the thermoelectric magnetic force (TEMF) and thermoelectric magnetic convection (TEMC) during directional solidification of Pb–Sn alloys have been studied. Numerical results reveal that the TEMF acts on the tip and bottom of the dendrite/cell. The value of the TEMF increases with the magnetic field and the maximal value of the force is of the order of 105N/m3 under a 10 T magnetic field. The above results should be attributed to the coupling effects between the TEMF and the magnetization force. Present work may initiate a new method to prepare the “aligned equiaxed grains” via an applied high magnetic field (B⩾8T) at a low growth speed (R⩽20μm/s) during directional solidification.

Comparison of surface effects in SiO2 coated and uncoated nickel ferrite nanoparticles

Magnetic properties of uncoated and silica coated nickel ferrite nanoparticles of comparable sizes have been studied in detail. Silica coated and uncoated nanoparticles were prepared by sol–gel and co-precipitation methods, respectively. Average crystallite size determined by X-ray diffraction is 12nm and 14nm for the silica coated and uncoated nanoparticles, respectively. Normalized saturation magnetization value of the coated nanoparticles was found to be lower than of uncoated nanoparticles, while a comparable small coercivity is observed for both the samples. Zero field cooled/field cooled (ZFC/FC) measurements reveal that the average blocking temperature (TB) of coated nanoparticles is lower than of the uncoated nanoparticles and is shifted to lower temperatures at high field. Thermoremanent magnetization (TRM) measurement indicates that the relaxation of coated nanoparticles have not been influenced very much with increasing cooling field as compared to uncoated nanoparticles and is attributed to enhanced surface effects in coated nanoparticles. The main source of enhanced surface effects in the coated nanoparticles is foremost disordered surface spins due to silica matrix. Temperature dependent AC susceptibility exhibits two peaks for the coated nanoparticles’ sample. First peak corresponds to blocking of huge core spin while second peak at lower temperature is may be due to enhanced surface effects (spin-glass behavior). All these findings such as lower saturation magnetization, faster shift of blocking temperature at high field, small effect of high magnetic field on magnetic relaxation, low temperature out-of-phase AC susceptibility peak for the coated nanoparticles signify enhanced surface effects in them as compared to uncoated nanoparticles.

Nonequilibrium currents in the quantum Hall effect regime spatially resolved by transport experiment

Eddy currents in a constriction placed in a two-dimensional electron gas (2DEG) have been experimentally studied. The constrictions fabricated by the electron-beam lithography demonstrate quantum Hall effect in high magnetic field. Pronounced hysteresis of magnetoresistance is observed at Hall plateaus corresponding to integer filling factors v = 1, 2 and 4 of a macroscopic 2DEG. The dependence of magnetoresistance hysteresis on the constriction width is obtained. The dependence contains the threshold value of width that points to the edge nature of eddy currents and enables us to determine the eddy currents area width, which is about 0.5 μm.

Atomic interdiffusion in Ni–Cu system under high magnetic field

The effect of high magnetic field on the atomic interdiffusion in Ni–Cu system was studied using the Cu/Ni/Cu diffusion couples. During the atomic interdiffusion in Ni–Cu system, it was found that the interdiffusion coefficients increased with the increase of molar fraction of Ni atoms in the interdiffusion zones when the couples were annealed with or without the magnetic field. It was noted that all corresponding interdiffusion coefficients under the magnetic field are smaller than those without the magnetic field. The results demonstrate that the magnetic field retards the atomic interdiffusion in Ni–Cu system. This retardation is achieved through reducing the frequency factors but not changing the interdiffusion activation energies.

The effects of high magnetic field on crystallization of Fe71(Nb0.8Zr0.2)6B23 bulk metallic glass

We report that the high magnetic field (HMF) retards crystallization, i.e. helps to keep a fully amorphous state of bulk metallic glass (BMG) upon isothermal annealing in the supercooled liquid region. Particularly, the application of HMF during an annealing process can effectively suppress the crystallization of boride (e.g. Fe23B6-type phase, or even a hard magnetic Fe2B phase) from the amorphous matrix of Fe71(Nb0.8Zr0.2)6B23 BMG. Thus by delaying crystallization, HMF can enhance the soft magnetic properties of high B content Fe-based bulk amorphous and nanocrystalline materials.

Effect of high magnetic field on diffusion behavior of aluminum in Ni–Al alloy

The effect of magnetic field on the diffusion behavior of aluminum in Ni–Al alloy was investigated using diffusion couple technique. The results indicated that the diffusion of aluminum in the direction parallel to the magnetic field was suppressed and the frequency factor pertaining to the diffusion coefficient was decreased without much variation of the activation energy. The inhibition of diffusion with magnetic field was discussed based on the ambipolar diffusion theory.

Adiabatic measurements of magneto-caloric effects in pulsed high magnetic fields up to 55 T

Magneto-caloric effects (MCEs) measurement system in adiabatic condition is proposed to investigate the thermodynamic properties in pulsed magnetic fields up to 55 T. With taking the advantage of the fast field-sweep rate in pulsed field, adiabatic measurements of MCEs were carried out at various temperatures. To obtain the prompt response of the thermometer in the pulsed field, a thin film thermometer is grown directly on the sample surfaces. The validity of the present setup was demonstrated in the wide temperature range through the measurements on Gd at about room temperature and on Gd3Ga5O12 at low temperatures. The both results show reasonable agreement with the data reported earlier. By comparing the MCE data with the specific heat data, we could estimate the entropy as functions of magnetic field and temperature. The results demonstrate the possibility that our approach can trace the change in transition temperature caused by the external field.

Fraunhofer-type absorption line splitting and polarization in confocal double-pulse laser induced plasma

Strong line splitting and polarization are observed in Fraunhofer-type absorption lines in Pb, Sn, Si, Cd, In, and Zn in confocal double-pulse laser induced plasma (DP-LIP) experiments. This effect is detectable using medium laser power densities: (~1–2)×1013W/m2 for the first laser pulse and 1×1014W/m2 for the second laser pulse. Polarization and splitting effects exist only during the second laser pulse (~7ns). Absorption line polarization and splitting phenomena may be explained by a high overall magnetic field and motional Stark effect caused by the second laser pulse inside the laser plasma created by the first pulse.

The accelerating effect of high magnetic field annealing on the interdiffusion behavior of Co/Ni films

The effects of high magnetic field annealing on the interdiffusion of Co/Ni bilayer films were investigated in this paper. A clear CoNi alloying zone can be observed by field emission scanning electron microscopy and energy dispersive spectroscopy, for samples annealed with and without magnetic field. Significant Co and Ni interdiffusion was verified by X-ray photoelectron spectroscopy. Based on the thickness of the diffusion layer, the distribution of atoms and the microstructure of interfacial products, the interdiffusion coefficients of the bilayer diffusion couples were calculated. Compared with the no-field case, the interdiffusion coefficient clearly increased when a high magnetic field of 12T was applied. This effect can be attributed to an increase in the chemical potential gradient induced by magnetic free energy in a high magnetic field.

Effects of high magnetic field on the quench behavior of Bi2Sr2CaCu2Ox coils at 4.2 K

The development of high field superconducting magnets using high temperature superconductors (HTSs) is progressing for high energy physics, nuclear magnetic resonance and energy storage applications. Yet the key issue of quench protection remains unresolved, primarily due to the slow normal zone propagation velocity (NZPV) in HTS magnets. High magnetic field may affect the quench behavior through two opposing effects: increased NZPV may result due to reduced critical temperature and current sharing temperature, but decreased NZPV may result due to reduced critical current density and thus operating current. At present it is unclear which effect dominates. Here, a series of quench experiments at high magnetic field on multilayer wind-and-react Bi2Sr2CaCu2Ox (Bi2212) coils addresses this question. The two- and three-dimensional quench behavior is investigated in a magnetic field up to 20 T at 4.2 K. With increasing magnetic field, the minimum quench energy decreases significantly. The NZPV also decreases with magnetic field, but only up to about 8 T. For magnetic fields above 8 T, the NZPV is independent of magnetic field up to at least 20 T. Thus, at low field the NZPV is dominated by the decreasing critical current density, whereas at higher magnetic field the competing effects of decreasing critical current density and decreasing temperature margin offset each other.

High pressures, low temperatures, and magnetic field effects on AgFeAsSe3 and AgFeSbSe3 properties

A procedure for synthesizing AgFeAsSe3 and AgFeSbSe3 is presented, and their electric and magnetic properties are investigated over a wide range of temperatures, pressures, and magnetic field variation. At 100–400K, the samples are characterized by semiconductor properties. Under pressures of ∼25 and ∼24 GPa, the electric properties of AgFeAsSe3 and AgFeSbSe3 change greatly.

Evolution of morphology in electrodeposited nanocrystalline Co–Ni films by in-situ high magnetic field application

The effect of high magnetic fields up to 12T, applied during electrodeposition process, on the morphology of nanocrystalline CoNi films has been investigated. The magneto-induced dramatic modifications in the morphology were observed by using field-emission scanning electronic microscopy and atomic force microscopy. Along with the increase of magnetic flux density (B), the grain size and the surface roughness of the films increased to reach a maximum value at a field of 9T. Meanwhile, higher magnetic flux density could improve cobalt atomic percentage in the film due to the impacts of magnetohydrodynamic effect. However, at a high field of 12T, the paramagnetic force played a predominant role in a decrease of mass transport, resulting in minimum grain size and roughness, even smaller than that of the ordinarily (B=0T) sample.

Isothermal heat treatments of an Al–4.8mass%Cu alloy under high magnetic fields

Isothermal heat treatment experiments of an Al–4.8mass%Cu alloy were carried out under different magnetic field intensities, at different temperatures and for different holding times. The influence of high magnetic fields on area fraction of θ phase in the solidified microstructure was investigated. It was found that the area fraction of the θ phase was lower when imposing the magnetic field compared to samples heat-treated without magnetic field. In other words, the magnetic field accelerated the phase transformation to the equilibrium state. In addition, the area fraction of the θ phase was independent of magnetic field intensity. This effect of high magnetic fields on the decreasing of the θ phase was discussed from the viewpoint of the effect of high magnetic fields on diffusion.

Effect of High Magnetic Field on Structure and Oxygen Adsorption of CuO Films

CuO films have been fabricated by a two-step method: depositing Cu films on single crystal Si substrates by magnetron sputtering; thermal oxidation of the as-deposited Cu films in the air at 600 degrees C. To investigate the effect of magnetic field on CuO film growth, a series of static fields are added along the substrate in the oxidation process. Field emission scanning electron microscopy shows that the high magnetic field promotes the densification and the grain refinement of the films. The X-ray diffraction results reveal that the films have monoclinic structure of CuO. The relative intensity of (111) peak strengthens gradually with increasing the magnetic field intensity, implying that the magnetic field facilitates the growth along [111] direction. X-ray photoelectron spectra of Cu 2p core-level indicate that +2 is the main valence state for Cu ions in CuO films, and the magnetic field produces deeper oxidation of the samples. The high binding energy part of O 1s XPS spectra, which reflects the oxygen adsorption ability, shrinks at low magnetic field, and then expands with the further increase of the magnetic field. The mediation of oxygen adsorption is related to the improvement of crystallinity as well as the enlarged boundary areas. The present study opens a new way to fabricate CuO films, and the high magnetic field is an effective way to tuning the oxygen adsorption.

EFFECT OF HIGH MAGNETIC FIELD ON CRYSTALORIENTATION,MORPHOLOGY AND MAGNETO-STRICTION OF TbFe 2 AND Tbo.27DYo.7sFe1.s5 ALLOYSDURING HEAT TREATMENT PROCESS

The rare–earth giant magnetostrictive materials are one kind of the most important functional materials now. The rare–earth giant magnetostrictive materials of TbFe2 and Tb0.27Dy0.73Fe1.95(R–Fe) alloys were firstly used in sonar system in military. Now, the applications of these two alloys have been developed widely in both industry and civil fields, such as magnetomechanical transducers, actuators, adaptive vibration control systems, and so on. The TbFe2 and Tb0.27Dy0.73Fe1.95 alloys both have the C15–type cubic Laves phase structure, which has strong magnetic anisotropy. This causes that the alloys exhibit different magnetostrictive properties along different crystal orientations. So, the preparation of high orientation degree magnetostrictive materials has a great of importance. In this work, it is predicted that the magnetostricive property of these two alloys can be enhanced with high magnetic field during heat treatment around their Curie and eutectic points. Therefore, a high magnetic field up to 11.5 T was imposed on these two kinds of R–Fe alloys during heat treatment at different temperatures in the experiments. Then the effects of high magnetic field on the crystal orientation, morphology and magnetostriction were analyzed in detail by XRD, metallographic microscope, and static resistance strain gauge. Also, the relationship between structure * K`W}h=dL+ 51006020, 51174056, KPe==osy3H3L+ 2011CB612206 'Jv T= }o9L+ N120409001, N120509001 ^W X: ℄A : 2013–05–28, X` ℄A : 2013–07–24 m8Nb : , ,, 1982 2m, zm DOI: 10.3724/SP.J.1037.2013.00289 9 AE` : KH0[A u TbFe2 ) Tb0.27Dy0.73Fe1.95 ,fl TO / [!)HEj _0^ K 1149 and property is discussed. The results showed that high magnetic field didn’t change the orientation of the R–Fe alloys, but the orientation degree had a great improvement after heat treatment. The phase composition of the two alloys had no change. However, the heat treatment with a magnetic field up to 11.5 T distinctly reduced the rare–earth phase of TbFe2 and obviously increased the magnetic phase. In addition, the magnetostrictive property of TbFe2 alloy increased after the heat treatment with high magnetic field. But for Tb0.27Dy0.73Fe1.95 alloy, the magnetostriction was not obviously enhanced. The reason for the improvement of the magnetostriction is that the Zeeman energy caused by high magnetic field increased the total Gibbs free energy of the system, which made the random orientation in crystals orient along the 〈113〉 direction, and enhanced the magnetostriction of the R–Fe alloys.