Diamagnetic domains and magnetostriction in beryllium

Magnetostriction was for the first time studied under the conditions of formation of diamagnetic domains (Condon domains). Transverse magnetostriction oscillations on a beryllium single crystalline plate oriented normally to magnetic field were measured in magnetic fields up to 7 T at temperatures down to 1.5 K. The relative amplitude of oscillations increased almost as the square of magnetic field and reached 10^?5. The signal had a sawtoothed shape corresponding to alternation of homogeneous and inhomogeneous (domain) states in the region of the existence of magnetic domains. The arising of domains was accompanied by singularities in the observed signals which is explained by an anomalous increase in the compressibility coefficient of the domain state: coefficient oscillations were more than 100 times larger than the value predicted by the standard theory. The observed relation between magnetization current and deformation led us to conclude that the compressibility of the metal was fully determined by conduction electrons. Magnetostriction then exactly compensated Fermi level oscillations. The position of the Fermi level therefore remained constant under magnetic field variations. In addition, the domain wall thickness had to increase as the plate grew thicker.     

Observation of diamagnetic domains in beryllium

We have observed diamagnetic domains (Condon domains) in a beryllium single crystal in magnetic fields H⩽3 T (H∥[0001]) at liquid-helium temperatures. The formation of the domain structure was determined according to magnetic-breakdown quantum oscillations of the resistance thermoelectric power as well as according to the splitting of the resonance peak of the free spin precession frequency of muons (μSR). The alternation of a uniform state (with one μSR peak) and a state with domain structure (with two peaks) is consistent as regards the periodicity with the de Haas-van Alphen effect, the period is ΔH≅78 Oe, and the range of existence of domains and the difference in their magnetizations are ΔB=4πΔM=B ₂−B ₁≅30 Oe. Fiz. Tverd. Tela (St. Petersburg) 40, 524–526 (March 1998)     

Specific features of the magnetic aftereffect in high-purity diamagnetic beryllium

The behavior of the effective shear modulus and low-frequency internal friction in magnesium-thermal beryllium condensate before and after the treatment of samples in a weak constant magnetic field has been studied. The data obtained have been used for calculating the temperature and time dependences of the ratio between the dislocation motion velocities during and after the magnetic action. It has been shown that the exposure of samples to a magnetic field and their aging after the magnetic action radically change the character of the temperature dependences of the dislocation motion velocities. Empirical expressions describing these dependences have been obtained. It has been demonstrated that the magnetic aftereffect in diamagnetic beryllium has a complex character, which indicates the presence of several magnetic memory mechanisms.     

Measurement of the stress sensitivity of magnetostriction in electrical steels under distorted waveform conditions

Electrical steel laminations used in the construction of transformer cores are subject to stresses introduced during their construction and analysis of the effect of this on the magnetostriction of the lamination has been investigated previously. It has been shown that higher harmonics of magnetostriction are of greater importance than the fundamental when considering transformer noise. Whereas previous studies have concentrated on the magnetostriction harmonics generated by sinusoidal magnetization, this investigation seeks to understand the relationship between harmonics present in the magnetization waveform and those in the magnetostriction waveform. A measurement system has been designed based on a similar principle to one previously described. In this case, a single Labview Virtual Instrument (VI) is used for the control of the applied stress, controlled magnetization and measurement of magnetostriction together with other magnetic parameters such as specific total loss, specific apparent power, permeability, coercivity and remanence. An adaptive digital feedback algorithm is utilized for control of arbitrary waveform which may be constructed from discrete harmonics or read from an input waveform. As well as measuring peak magnetostriction the software utilizes an FFT to calculate the harmonics of magnetostriction at each stress point. The effect of harmonics introduced into the magnetization waveform on the magnetostriction harmonics will be shown at various applied stresses. A harmonic, Harm_B in the flux density waveform is shown to have the effect of producing a dominant harmonic in the magnetostriction given by (Harm_B+1)/2.     

Influence of magnetostriction on the domain structure of cobalt

The paper presents the calculation of the energy of elastic stresses in the domain structure of uniaxial massive ferromagnetics. The inclusion of this energy permits the formation of a structure with walls perpendicular to the external field to be elucidated and the critical thickness of the sample on which this structure is realized to be determined.     

Penetration of long strikers under hydrodynamic conditions with allowance for the material compressibility

The influence of compressibility on the fast penetration of long metallic strikers into different barriers at interaction speeds of up to 10 km/s is investigated. The investigation is based on the hydrodynamic theory of penetration. Compressibility-related corrections to Lavrent’ev’s rate and depth of penetration, which were obtained in terms of the concept representing the penetration process as collisions of ideal incompressible liquid jets, are estimated. The variation of these corrections with the interaction speed under subsonic and supersonic conditions is analyzed. If the compressibilities of the striker and barrier materials differ radically, the penetration depth disagrees with that predicted by the hydrodynamic theory (assuming the incompressibility of the materials) by 10–15%.     

Anomalous compressibility and metallization of deuterium and hydrogen at high pressures

The high compressibilities recorded in experiments on liquid-deuterium compression and the significant scatter of experimentally measured densities in the region of anomalous compressibilities are explained by the manifestations of an unusual dielectric-metal phase transition: from a dense molecular gas to a liquid-metal atomic gas. This transition has previously been described by us and called the dissociative phase transition (DPT). The dissociative equilibrium curves, the isotherms, the DPT binodal, and the Hugoniot adiabat have been calculated. The DPT has been shown to be a transition of a new, non-van der Waals type.     

Coulomb ensemble of charged diamagnetic macroparticles in an inhomogeneous magnetic field under microgravity conditions

The formation of strongly nonideal Coulomb systems of a large number (∼104) of charged diamagnetic macroparticles in a cusp magnetic trap under microgravity conditions has been experimentally studied. The experiments have performed in the Russian segment of the International Space Station in the framework of the Coulomb Crystal experiment. Using the data of the videorecording of the positions of the particles in the magnetic trap, the magnetic susceptibility and charge of the particles have been estimated and the period of the oscillations of the cloud of the particles, as well as the damping rate of oscillations, has been determined.     

Coulomb scatter of diamagnetic dust particles in a cusp magnetic trap under microgravity conditions

The effect of a dc electric field on strongly nonideal Coulomb systems consisting of a large number (~10⁴) of charged diamagnetic dust particles in a cusp magnetic trap are carried out aboard the Russian segment of the International Space Station (ISS) within the Coulomb Crystal experiment. Graphite particles of 100–400 μm in size are used in the experiments. Coulomb scatter of a dust cluster and the formation of threadlike chains of dust particles are observed experimentally. The processes observed are simulated by the molecular dynamics (MD) method.     

Non-linear behaviour of diamagnetic moments in Condon domain phase

A model for non-linear behaviour of a magnetization in strong de Haas van Alphen effect is proposed. It describes correctly measured values of the magnetic induction splitting due to Condon domains in silver, beryllium and aluminium. It is shown that the characteristics of magnetization curve in Condon domain phase depend on temperature, magnetic field and Dingle temperature.     

X-ray studies of the domain formation in rocks under blasting

Quartz plates placed in concrete are used to model the rock blasting procedure. Quartz fragments resulted from blasting are studied by small-angle X-ray scattering. Obtained grains in the quartz fragments are approximately 200–220 nm in size. The samples are discovered to contain low-dimensional (linear) components; the further the sample is from the explosion center, the coarser the grains are in it. Superlattice parameters of the studied fragments are estimated. It is suggested that domain boundaries in the sample quartz fragments are linear objects, such as dislocation walls.     

Magnetophoretic concentrating of diamagnetic bio-particles and formation of liquid-crystalline chromatin structures

The packing of chromatin during the self-assembly was modeled with a diamagnetic compression achieved under a gradient magnetic separation (magnetophoresis). Nucleoprotein granules separated from cultivated connective tissue and nuclei of chicken red blood cells formed various chromatin mesophases and chiral supra-molecular structures. The applied magnetic pressure accelerated mesophase formations due to the diamagnetic alignment and the concentrating of nucleosome nanoparticles and aggregates (germs) in gradient magnetic fields. Under various magnetic force parameters (H · grad H) ∼ 10⁵–10¹¹ Oe²/cm the different mesophases emerged. Chicken nucleated red blood cells were found to be a convenient model to study the chromatin condensation under influences including electromagnetic factors.     

Change of sign of the magnetostriction of iron under compressive stress

A spectacular change of sign of the magnetostriction of carefully annealed polycrystalline iron rods is observed by applying a compressive stress as small as 200 g mm^-2. This effect is interpreted in terms of the displacement of the 90° domain boundaries.     

On the cryogenic layer formation under conditions of high-frequency mechanical action

The results of a series of experiments using a piezovibration formation module for producing cryogenic targets with a given fuel layer structure are presented.     

Anomalous thermal expansion and spontaneous magnetostriction of Gd2Fe16Cr compound

The structural and the magnetic properties of Gd 2 Fe 16 Cr compound are investigated by x-ray diffraction and magnetization measurements.The Gd 2 Fe 16 Cr compound has a rhombohedral Th 2 Zn 17-type structure.There exist an anisotropic strong spontaneous magnetostriction and a negative thermal expansion in the magnetic state of Gd 2 Fe 16 Cr compound.The average thermal expansion coefficient ā=-7.03 × 10-6 /K in a temperature range of 294-454 K and ā=-1.31 × 10-5 /K in 454-572 K are obtained.The spontaneous magnetostrictive deformation and the Curie temperature are discussed.     

The formation of defects in Si under the radiation enhanced diffusion conditions

A review is given of recent developments in the study of magnetic (localized) photo-excitations in ionic solids. Emphasis will be on three topics: (i) the importance of magnetic properties in the structural characterization of defects, (ii) photo-chemical reactions as revealed from magnetic interactions in point defects, and (iii) energy and phase relaxation dynamics in photo-excited colour centres as probed from magnetic transients. In our survey we will focus on defects photo-excited to phosphorescent triplet states. In discussing a number of dynamical processes, some attention is given to the application of (optical-microwave) coherence spectroscopy which holds considerable promise for future work.     

Reversible formation of aryloxenium ions from the corresponding quinols under acidic conditions

Quinols, 1, are products of the hydration of O‐aryloxenium ions, 2, and N‐arylnitrenium ions, 3, and they are being investigated for medical uses. Under acidic conditions (pH 1–3) kinetics and products of Br^– trapping demonstrate that 1a, 4‐phenyl‐4‐hydroxy‐2,5‐cyclohexadienone, and 1b, 4‐p‐tolyl‐4‐hydroxy‐2,5‐cyclohexadienone, generate the corresponding oxenium ions 2a and 2b, respectively, as steady‐state intermediates. Formation and trapping of the oxenium ions occurs in competition with the acid catalyzed dienone–phenol rearrangement. Because oxenium ion formation is reversible, the ion can only be detected by trapping with a nucleophile. Br^– is an efficient trap under acidic conditions because, unlike N₃^–, it is not protonated under those conditions. Attempts to detect the oxenium ions 2a and 2b at pH 4.6 and 7.1 with N₃^– were unsuccessful indicating that oxenium ion formation only occurs under acidic conditions. The oxenium ion 2c could not be detected under acidic conditions from the quinol 1c, 4‐(benzothiazol‐2‐yl)‐4‐hydroxy‐2,5‐cyclohexadienone, by Br^– trapping methods, even though this ion can be detected during hydrolysis of the corresponding ester, 4c. Although the benzothiazol‐2‐yl group is a resonance electron donor that is capable of stabilizing an O‐aryloxenium ion, it is also a strong inductive electron withdrawing group that hinders the formation of 2c from 1c by decreasing the extent of protonation of 1c to generate 1cH⁺ and by destabilizing the transition state for ionization of 1cH⁺. Generation of an oxenium ion from the corresponding quinol is feasible under acidic conditions as long as the 4‐substituent of the quinol is both a resonance and inductive electron donor. Copyright © 2012 John Wiley & Sons, Ltd.     

非连续运行工况下结霜动力因素实验分析

冷风机表面在非连续运行工况下结霜是实际运行中经常遇到的问题,其影响因素较为复杂。通过建立结霜实验台,系统分析了影响非连续运行工况下冷风机表面结霜的因素,包括运行比、相对湿度及冷风机表面温度,并且对实验结果总结了关联式。结果表明,在非连续工况中,结霜量是一个与运行比有极大关系的值,而拟合的关联式则体现了这种关系,并与实验结果有较小的误差。