Capillary hydrodynamic effects in high magnetic fields

Cr‐doped ZnO diluted magnetic semiconductor (DMS) nanorods with nominal composition of 1 at.% were synthesized by a hydrothermal method with the assistance of a high pulsed magnetic field (HHPMF). All the Cr‐doped ZnO samples obtained with or without the applied high magnetic field exhibited room‐temperature ferromagnetic behavior. It is observed that the high magnetic field plays an important role in saturation magnetization of the samples. The effects of high magnetic field on the morphology, structure, and magnetic properties of the samples were discussed.

Tunable phase formation in Ni–Fe thin films at nanoscale using high magnetic fields

Recently, the studies on the effects of high magnetic fields on solidification processes have been paid much attention both from the fundamental and applied points of view. With the aid of the enhanced Lorentz force and magnetization effect caused by the remarkably increased magnetic field intensity, several interesting phenomena, such as the control of fluid flow and particle migration in a melt, crystal orientation, and phase alignment, have been obtained. Moreover, the magnetic force induced by the interaction of magnetization and high magnetic field gradient has been evidenced to show significant effects on the microstructure evolution of alloys. In this paper, the recent development of the control of the solidification process by high magnetic fields is reviewed from the view point of uniform magnetic fields and magnetic field gradients.

This paper summarizes our recent work on the application of high static magnetic fields to the austenite-to-ferrite transformation and the tempering processes in hot-rolled 42CrMo steel. The thermodynamic and kinetic effects of the high magnetic fields on austenite decomposition and the influences of the high magnetic field on carbide precipitation and the matrix recovery during high- and low-temperature tempering are briefly outlined. Insight into these aspects may provide better understanding of the effects of high magnetic fields on diffusional phase transformations and is of both theoretical significance and technical interest.

The effect of a high magnetic field on carbide precipitation in W6Mo5Cr4V3 high-speed steel during low-temperature tempering was investigated. The applied high magnetic field promoted the precipitation of M 6C-type carbides at boundaries and in the grain interior, but maximum spheroidization and refinement occurred for those carbides precipitated at boundaries. Compared with M 6C-type carbides, the effect of high magnetic field on the precipitation behavior of MC-type carbides is much weaker. The high magnetic field hindered M 2C-type carbide precipitation by affecting the Gibbs free energy and increased the microhardness of W6Mo5Cr4V3 high-speed steel at low tempering temperature.

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.

Carbon nanotubes and fullerenes were synthesized by arc discharge in a He gas atmosphere under a high magnetic field up to 10 T. Morphology and the yield of these nanotubes were investigated by scanning electron microscopy and transmission electron microscopy (TEM). The yield and type of fullerenes were also evaluated by ultraviolet visual spectroscopy. TEM images revealed that thin collapsed nanotubes having larger curvature were synthesized under a high magnetic field, in particular at 10 T. Furthermore, the ratio of C70 to C60 concentration was found to vary depending on the magnitude of the magnetic field during arc discharge. Based on these results, the effects of magnetic field on the synthesis of carbon nanotubes and fullerenes are discussed.

The effects of high magnetic fields on the solidification microstructure of Al–Si alloys were investigated. Al–7.2 wt%Si and Al–11.8 wt%Si alloys were solidified in various high magnetic fields at different cooling rates. The secondary dendrite arm spacing (SDAS) of the primary Al dendrites and the lamellar spacing (LS) of the eutectics were measured. It was found that the application of a high magnetic field could decrease the SDAS of the primary Al dendrites in Al–7.2 wt%Si alloys and the LS of the eutectics in Al–11.8 wt%Si alloys. The effects of the high magnetic field on the SDAS decreased with increasing cooling rate. The decrease in the SDAS and LS can be attributed to the decrease of the solute diffusivity in the liquid ahead of the solid/liquid interface during the growth of the dendrite and eutectic. This decrease is caused by the high magnetic field which can damp the convection and avoid its contributions to the diffusion.

This chapter aims at reviewing magnetic field effects (MFE) in organic light emitting diodes (OLED) with an emphasis on our study under high magnetic field up to 9 T. This subject includes organic spintronics in general, which is a hot subject attracting many researchers recently. Since singlet-triplet conversion in excitons is critically important in the current efficiency of OLEDs, spintronics aspects of OLEDs should be studied in detail. However, due to the difficulty in the fabrication of stable devices, the number of the researches has been limited. We have found two things up to now, by making very stable OLEDs and measuring them under high magnetic fields. (1) Efficiency of OLEDs decreases quadrically with the magnetic field up to 6 T and the rate of decrease becomes smaller between 6T and 9T. (2) Minority carrier conductivity decreases linearly with the magnetic field, whereas that of majority carrier is almost constant. (3) Anomalous behaviors (large magnetoresistance etc.) are only seen in bipolar injection, which agrees with previous reports. Although the mechanisms behind these findings have not been clarified yet, some hypotheses have been made with the analogy with MFE on chemical reactions. In principle, MFE on charge transport and recombination has similarity with chemical reaction under magnetic field, and the terminology and concept should be parallel between these subjects. We will try to combine the current knowledge of organic charge transport, OLEDs, spintronics and MFEs of chemical reaction to make a unified picture of these issues.

Crystallization behavior of Fe84B10C6 amorphous alloy under high magnetic field

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.

Phase alignment and crystal orientation of Al 3Ni in Al–Ni alloy by imposition of a uniform high magnetic field

Mn-898wt%Sb alloys were solidified in the absence or presence of high magnetic fields of 88 T with various gradients to investigate the effects of high magnetic fields on the structures of the alloys. It was found that both of the two primary phases, i.e. MnSb and Sb appeared simultaneously in MnSb/Sb eutectic matrix and the MnSb and Sb phase-rich layers were aggregated in different domains under high gradient magnetic field conditions. It was also found that the volume fraction of these two primary phases increased with the increase of the field gradient. This process was attributed to that the alloying element clusters with different susceptibility in molten state were driven along or opposite to the direction of magnetic forces when subjected to high gradient magnetic fields and thus resulted in a layered microstructure with compositional gradient. The results of present study suggest that adjastment of high gradient magnetic field may potentially be used to tailor functionally graded materials.

Growth of diffusion layers at liquid Al–solid Cu interface under uniform and gradient high magnetic field conditions

Effects of high magnetic field annealing on microstructure and multiferroic properties of Bi1−xLaxFeO3 ceramics