Atoms in high magnetic fields (white dwarfs)

Interdiffusion and magnetic properties of Co/Cu/Co trilayers produced by high magnetic field annealing

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.

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.

Influence of interdiffusion on the magnetic properties of Co/Si (100) films after high magnetic field annealing

THE circular polarization1–4 of the light emitted from some white dwarf stars suggests1–3 that these stars have associated magnetic fields of 106 to 107 gauss. A variation in the circular polarization with a periodicity of about one day was also observed5 in one case. Large magnetic fields and small rotation periods can in principle occur if compact bodies are formed by catastrophic compression in nova or supernova explosions; such catastrophic compression can yield, for a white dwarf star, a magnetic field as high as 108 gauss and rotation periods of 10 to 100 s, the lower periods being associated with higher magnetic fields and vice versa. Thus it is possible to have white dwarf stars with a rotation period P of 10 s, magnetic field, B, of 108 gauss, radius R of 109 cm, and mass M of about 0.5 M⊙ On the other hand, white dwarf stars can perhaps also be formed by a gentle mass loss by the parent star; these will have substantially lower magnetic fields and larger periods than given above.

A study of hot-carrier effects in the presence of high magnetic fields in $p$-type silicon inversion layers is reported in a range of lattice temperatures between 1.25 and 20 K. Carrier temperatures ${T}_{c}$ as a function of the electric field are deduced from measurements of the amplitude of Shubnikov-de Haas oscillations as a function of lattice temperature ${T}_{L}({T}_{L}l10 \mathrm{K})$ and electric field $E$ at high inversion-layer densities for the (110) orientation. For higher lattice temperatures, ${T}_{c}$ is deduced from the classical magnetoresistance. In addition, measurements of the surface conductivity $\ensuremath{\sigma}$ as a function of the source drain electric field at low hole concentrations, where $\ensuremath{\sigma}$ depends on the temperature and the surface orientation, have been performed. It is found $\ensuremath{\sigma}$ is proportional to ${E}^{s}$ with $0\ensuremath{\le}s\ensuremath{\le}3$ over nearly two decades of $E$ values.

Pronounced modification of the wetting and spreading behavior of molten Ag-Cu alloy on TC4 substrate in response to high magnetic fields

High magnetic field is an important research condition which can provide great opportunities for the development of many subjects. Since 1913, there are 19 Nobel Prizes which are related to high magnetic field. Scientific research under high magnetic field involves a large amount of subjects and various scientific issues. In many research areas such as the quantum transport in semiconductors, Fermi surface measurements, the study of the upper critical field of high temperature superconductors, nuclear magnetic resonance study etc., high magnetic field is an essential condition. Therefore, the scientific research under high magnetic field is always the frontier. In this review, the cutting-edge scientific issues under high magnetic field are presented. The issues in physics include the fractional quantum Hall effect in graphene, the quantum oscillations in black phosphorus, the topological insulator Bi2Se3, the Weyl semimetal NbP, the quantum ordering in non-conventional superconductor, the magnetic field induced new superconducting phase, the magnetic field induced metamagnetism transition, the quantum effect of low dimensional materials, the spin frustration, etc. In chemistry and material science, the focuses are magnetic field induced new chemical reaction, control of reaction routes, the reaction kinetics, synthesis of single molecular magnet and chiral materials, nano-catalysis, etc. Issues related to nuclear magnetic resonance are also mentioned, including the protein structure determination, magnetic resonance imaging for medical science, the structure of melt, geosciences and environmental sciences, etc. Moreover, the present condition and achievement of the high magnetic field facility in China are shown in the following part. Three water-cooled magnets have created three world records. The water-cooled magnet WM1 with a 32 mm bore can generate a steady magnetic field of 38.5 Tesla, which has exceeded the previous record 37.5 Tesla. The water-cooled magnet WM5 with a 50 mm bore has produced a magnetic field of 35 Tesla, which is also the highest for the same type of magnets. The water-cooled magnet WM4 with a 32 mm bore has generated a magnetic field of 27.5 Tesla when inputting 10 MW power. All the magnets have corresponding experimental systems. For example, WM1 has a 3He extreme low temperature experiment dewar installed providing a temperature region from 325 mK to 70 K, which is mainly used for transport measurement. The high-homogeneity water-cooled magnet WM2 has a high field high frequency (82 to 690 GHz) electron magnetic resonance continuous wave system installed. WM5 can cooperate with a Fourier transform infrared spectroscopy (18000 to 4000 cm - 1), a vibrating sample magnetometer for magnetization measurement, and a high pressure experiment system (0–200 GPa). The service of the high magnetic field facilities in China will provide strong support for various cutting-edge research and create advantage for significant original achievement.

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.

A set of hydrodynamic equations has been applied to processes occurring in non-conductive fluids placed into magnetic fields. The equations are valid for equilibrium magnetization within the framework of a continuous medium. The ranges of physical parameters have been evaluated for which magnetization of a fluid should be taken into account in problems concerning the determination of equilibrium forms, and flows and their stability. The conclusion has been drawn that magnetization of natural fluids in these problems must be taken into consideration for fluids in high (exceeding 1 T) magnetic fields. As examples, the solutions of several typical problems concerning the equilibrium surface of capillary fluids and their stability in external magnetic fields have been considered. Hydrodynamic effects related to magnetization of natural capillary fluids in high magnetic fields are studied with due regard for the above solutions. Hydrodynamic effects in para- and diamagnetic fluids have been studied and the common and distinctive features of these effects discussed.

Coulomb screening and weak interactions in a hot, magnetized plasma are investigated. Coulomb screening is evaluated in a relativistic thermal plasma in which electrons and positrons are in equilibrium. In addition to temperature effects, effects on weak screening from a strong external magnetic field are evaluated. In high fields, the electron transverse momentum components are quantized into Landau levels. The characteristic plasma screening length at high temperatures and at high magnetic fields is explored. In addition to changes to the screening length, changes in weak interaction rates are estimated. It is found that high fields can result in increased β-decay rates as the electron and positron spectra are dominated by Landau levels. Finally, the effects studied here are evaluated in a simple r-process model. It is found that relativistic Coulomb screening has a small effect on the final abundance distribution. While changes in weak interaction rates in strong magnetic fields can have an effect on the r-process evolution and abundance distribution, the field strength required to have a significant effect may be larger than what is currently thought to be typical of the r-process environment in collapsar jets or neutron star mergers. If r-process sites exist in fields G, effects from fields on weak decays could be significant.

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 wall relaxation time for optically pumped 〈Sz〉 polarized sodium atoms colliding with copper, stainless-steel, and dry-film coated surfaces has been measured as a function of an applied magnetic field. Results show that the mean number of wall collisions increases from one to about four before depolarization of sodium atoms occurs on a copper wall in a high (12 kG) magnetic field, whereas the atoms relax after a single collision on a stainless-steel wall even in high fields. The relaxation time for a dry-film coated surface, for the cell geometries used in our work, is dominated by the effusion of polarized sodium atoms from the cell. Our measurements also allow an estimate of the strength of the local magnetic field causing the 〈Sz〉 depolarization and of the correlation time of the depolarization interaction on the surface. The importance of these experimental results as applied to the performance of optically pumped polarized ion sources is also discussed.

Monte Carlo investigation of diluted antiferromagnets in high magnetic fields

Crystallization behavior of Fe84B10C6 amorphous alloy under high magnetic field