The effect of pulsed magnetic fields on Cz-Si crystals

It has been established that short-term effects of pulsed magnetic fields initiate long-term low-temperature decay of a supersaturated solid solution of oxygen in silicon crystals grown by the Czochralski method (Cz-Si), which results in the generation of oxygen-containing defects in the form of O-V centers and more complicated Si_xO_yV_z complexes, where V is a vacancy. The process of defect formation after the action of the pulsed magnetic fields culminates in the formation of spatially ordered oxygen-vacancy clusters and/or the precipitation of oxide phases, depending on the original defects present in the crystal. The action of such fields also initiates crystallization of an amorphized layer when it is present on the surface of the original crystal. The detected effects are characterized by a threshold field strength, are accumulate with successive pulses, and reach saturation in terms of these parameters of the action. The effects induced in Cz-Si crystals by pulsed magnetic fields are analyzed in terms of a possible cause consisting of the excitation of the Si-O bond of an interstitial oxygen by nonequilibrium population of the vibrational levels of a metastable electronic term of the bond. Zh. éksp. Teor. Fiz. 111, 1373–1397 (April 1997)     

Fracture of spheroplastic under static and dynamic stressing

The fracture of a composite material, a spheroplastic consisting of a polyester resin matrix and glass microspheres as a filler, is studied experimentally and theoretically under static and dynamic stressing. A shock is generated by a pulsed magnetic field. The fracture type in relation to the shock parameters and material structure is analyzed. A method for testing the dynamic behavior of the material based on the incubation time accumulation is suggested.     

Internal friction in a magnetically treated material with dislocations

Internal friction of magnetically treated tin-bronze has been investigated as a function of the degree of dislocation pinning caused by an impurity-defect atmosphere. It is found that pulsed magnetic field treatment of this material can affect its internal friction in different ways. After pulsed magnetic field treatment the level of internal friction can be higher than in the untreated material if, as a result of aging processes preceding this treatment, a dislocation impurity-defect atmosphere is formed, and can be lower if a qualitatively new impurity-defect atmosphere is formed on the dislocations as a result of earlier treatment, or it can remain unchanged in the absence of atmospheres at the dislocations. The observed character of of internal friction in pulsed magnetic field treated material is linked with the presence of localized magnetically active centers excited by such treatment, which can lead to a change in the interaction energy of the atmosphere with a dislocation. Fiz. Tverd. Tela (St. Petersburg) 39, 1234–1236 (July 1997)     

Effect of the inner structure of domain walls on the stability of an isolated stripe domain in a pulsed field

This paper studies the effect of the inner structure of domain walls on the stability of an isolated stripe domain localized in a thin ferromagnetic film against a pulse of magnetic field applied perpendicularly to the film surface. It is found that the value of the critical amplitude of the pulsed signal strongly depends on the value of the magnetizing field in which the system was initially placed. It is also established that the difference on stability of domains with unipolar and bipolar walls in pulsed fields diminishes as the amplitude of the magnetizing field decreases. Finally, the dependence of the region of stability in a pulse field on the parameters of the system is determined for various domain types. Zh. éksp. Teor. Fiz. 116, 1694–1705 (November 1999)     

Behavior of the glass transition and crystallization temperatures of the oxide glass MgO-Al2O3-SiO2 under external influences

The kinetics of the glass transition Tg and crystallization Tcr temperatures of the glass MgO-Al₂O₃-SiO₂ is studied under conditions of annealing in the glass transition interval and after treatment with a pulsed magnetic field (PMF). It is found that all the parameters studied exhibit nonmonotonic and intercorrelated variations in time. These temporal variations are due to structural relaxation (SR) in the glass. It is observed that a relative decrease of T _g and T _cr occurs in the annealed or PMF-treated glass. This effect is important from the standpoint of modern ideas about the mechanisms of structural relaxation and is due to the concentrational redistribution of chemical bonds. The condition for externally induced anomalous behavior of the temperatures investigated is determined. Zh. Tekh. Fiz. 67, 30–34 (October 1997)     

The effect of magnetic and electric fields on the state of point defects in single-crystal NaCl

It is established that exposing crystals to a pulsed electric field with an amplitude of ∼10³ kV/m creates metastable states of the point defects, while a magnetic field with an induction of 7 T causes them to relax. Fiz. Tverd. Tela (St. Petersburg) 40, 2184–2188 (December 1998)     

Dislocations used to probe the defect state of an ionic crystal lattice excited by a pulsed magnetic field

This paper presents the results of an investigation into the effect of a pulsed magnetic field on the state of linear and point defects in ionic crystals. For different amplitudes (1–7 T) and pulse lengths (3×10⁻⁵ to 10² s) of the pulsed field the kinetics of the transformation of defects into a new state and their relaxation after the field is turned off are studied in the temperature range 77–400 K. It is found that the relaxation of the states of point defects is mainly through recombination, and the change of state of the dislocations and of the point defects contribute nonadditively to the change in the dislocation mobility. The exposure of the crystal to a magnetic field leads to an increase in the dislocation mobility when the sample is mechanically stressed and to a decrease in the dislocation displacement with a second field pulse. Fiz. Tverd. Tela (St. Petersburg) 39, 634–639 (April 1997)     

Correlation properties of the stochastic magnetic structure of ultradispersed ferromagnetic materials

The properties of the stochastic magnetic structure of ultradispersed ferromagnetic materials are studied. The correlation coefficients of the magnetization of a magnetic material are calculated for various types of chaos in the anisotropy field. The effects of different types of disorder on the parameters of a stochastic magnetic structure are compared. Numerical simulations by various methods confirm the theoretical results. Fiz. Tverd. Tela (St. Petersburg) 41, 1432–1436 (August 1999)     

Formation of correlated states and tunneling for a low energy and controlled pulsed action on particles

We consider a method for optimizing the tunnel effect for low-energy particles by using coherent correlated states formed under controllable pulsed action on these particles. Typical examples of such actions are the effect of a pulsed magnetic field on charged particles in a gas or plasma. Coherent correlated states are characterized most comprehensively by the correlation coefficient r(t); an increase of this factor elevates the probability of particle tunneling through a high potential barrier by several orders of magnitude without an appreciable increase in their energy. It is shown for the first time that the formation of coherent correlated states, as well as maximal |r(t)|_max and time-averaged 〈|r(t)|〉 amplitudes of the correlation coefficient and the corresponding tunneling probability are characterized by a nonmonotonic (oscillating) dependence on the forming pulse duration and amplitude. This result makes it possible to optimize experiments on the realization of low-energy nuclear fusion and demonstrates the incorrectness of the intuitive idea that the tunneling probability always increases with the amplitude of an external action on a particle. Our conclusions can be used, in particular, for explaining random (unpredictable and low-repeatability) experimental results on optimization of energy release from nuclear reactions occurring under a pulsed action with fluctuations of the amplitude and duration. We also consider physical premises for the observed dependences and obtain optimal relations between the aforementioned parameters, which ensure the formation of an optimal coherent correlated state and optimal low-energy tunneling in various physical systems with allowance for the dephasing action of a random force. The results of theoretical analysis are compared with the data of successful experiments on the generation of neutrons and alpha particles in an electric discharge in air and gaseous deuterium.     

Characteristics of the statistical distribution of the current transmitted by a cathode spot of a vacuum arc in variously oriented magnetic fields

The influence of variously oriented uniform magnetic fields on the cathodic attachment of a low-current vacuum arc with electrodes made of oxygen-free copper and CuCr30 composition is studied. It is found that, if the current is fixed, cathode spots in the arc attachment are distributed by the normal law in the entire range of variation of the amplitude of magnetic induction vector B and angle α between this vector and the normal to the cathode surface. The parameters of the distribution depend on the magnetic field and cathode material. The magnetic field dependence is appreciable only when angle α exceeds some critical value α* (α* ≈ 30° and ≈45° for cathodes made of copper and CuCr30, respectively). At α > α*, the parameters of the distribution become strongly dependent on α, while the B dependence remains weak. Only when α → π/2 does the field amplitude have a pronounced effect on the parameters of the distribution. From the obtained results, we determine the statistical characteristics of the distribution of the mean current transmitted by a cathode spot in variously oriented magnetic fields. The found relationships make it possible to explain the peculiarities of the structure of the cathodic attachment of the high-current vacuum arc stabilized by an external axial magnetic field.     

Optimization of the parameters of a two-coil magnetic system for the generation of a uniform field with power supply from the line or a capacitor bank

Physical experiments often require the generation of a short-lived magnetic field with specified limits of nonuniformity. Various energy storage units, specifically capacitor banks, are used to supply pulsed power to the magnetic system. The simplest configuration of such a magnetic system is formed by two identical coaxial electromagnetic coils. In this work the parameters of this system configuration are optimized, subject to field uniformity requirements. Zh. Tekh. Fiz. 67, 101–106 (April 1997)     

Change in the absorption spectra of blood exposed to a low-frequency magnetic field

We have used the absorption spectra of whole blood in the UV-visible and IR regions of the spectrum to study changes in the structure of the molecular components of blood when exposed to a low-frequency pulsed magnetic field used to treat ischemic heart disease. We show that pronounced changes in the spectra when the blood is directly exposed in vivo to a magnetic field may be due to breaking of the bond between the heme group and the protein of the hemoglobin, as a consequence of changes in the intermolecular interactions in the polypeptide chains of the hemoglobin and also the spin states of the paramagnetic heme components. Exposure to a magnetic field results in changes in the conformations of the polypeptide chains of hemoglobin and the rate of dissociation of oxyhemoglobin. The structural changes in the hemoglobin molecule are considered as one of the possible primary mechanisms of action on blood in vivo for a low-frequency pulsed magnetic field. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 199–204, March–April, 2007.     

脉冲磁场对水热法制备Mn掺杂ZnO稀磁半导体的影响

本文以Zn(CH₃COO)₂·2H₂O, Mn(CH₃COO)₂·4H₂O和氨水缓冲溶液为原料, 在4 T脉冲磁场下利用水热法制备了Mn掺杂ZnO稀磁半导体晶体, 通过X射线衍射、 扫描电子显微镜、透射电子显微镜、拉曼光谱、荧光分光光度计及振动样品磁强计等对样品的微观结构及磁性能等进行了表征, 结果表明: Mn掺杂ZnO稀磁半导体晶体仍保持ZnO六方纤锌矿结构, 4 T脉冲磁场下合成的Mn掺杂ZnO稀磁半导体晶体具有明显的室温铁磁性, 其饱和磁化强度(M_s)为0.028 emu/g, 比无脉冲磁场下制备的样品提高一倍以上, 且4 T 脉冲磁场将样品的居里温度提高了15 K.     

Crossover effects in scheelite DyLiF4

The Zeeman effect, magnetization, and differential susceptibility of a DyLiF₄ crystal in a pulsed magnetic field are studied experimentally and theoretically. It is found that Dy³⁺ ion levels in DyLiF₄ approach each other and a crossover occurs in a magnetic field H ‖ [001], which leads to a smearing of peaks in the differential magnetic susceptibility dM/dH and to inflection points in the magnetization curves M(H) at low temperatures. It is demonstrated that magnetic anomalies that accompany the crossover in DyLiF₄ in a field H ‖[001] are sensitive to the electronic structure of the Dy³⁺ ion. Therefore, these anomalies can be used to refine the crystal-field parameters. The effects of variations in the crystal field and temperature and of a deviation of the direction of the magnetic field from the symmetry axis on the magnitude and character of the magnetic anomalies associated with the crossover are investigated. The crystal field and crossover effects in the scheelite structure are compared with those in the zircon structure.     

Influence of the rate of increase in the induction on the spectral characteristics of luminescence of ZnS: Mn under treatment in a magnetic field

This paper reports on the results of the investigation of photoluminescence and luminescence excitation spectra of a ZnS powder thermally doped with MnCl · 4H₂O or MnS and subjected to a series of treatments in a pulsed magnetic field with the same maximum amplitude of the magnetic field induction (B _max = 0.3 T) but with different rates of its increase $ \dot B $ \dot B (t) to a maximum value. It has been revealed that pulsed magnetic fields with different rates of increase in the induction B nonlinearly affect the spectral characteristics of the ZnS: Mn compounds. The processes occurring in the material, which can lead to a change in its spectral characteristics due to the manifestation of the magnetoplastic effect, and the influence of the parameter $ \dot B $ \dot B (t) of the magnetic field on the efficiency of the external action have been discussed. It has been demonstrated that a variation in the parameter $ \dot B $ \dot B (t) makes it possible to control the location of defects in the nearest environment of Mn²⁺ ions in the ZnS compound after the completion of treatment of the material in a magnetic field. The mechanisms responsible for the different effects exerted by energetically identical external disturbances on the system have been proposed.     

强磁与应力场耦合作用下AZ31镁合金塑性变形行为

研究强磁场对AZ31镁合金塑变能力和微观组织的作用,在3 T脉冲强磁场条件下对合金进行磁场耦合应力时的拉伸实验.采用电子背散射衍射、Ⅹ射线衍射和透射电镜分析等方法研究材料的微观组织.结果表明:与0 T拉伸试样相比,3 T拉伸试样抗拉强度和延伸率分别提高了2.2%和28.7%,说明将强磁场耦合作用于材料塑性变形过程时,能在不降低材料强度的同时提高镁合金的塑性变形能力,有助于同步改善材料强韧性.磁场作用机理主要表现为磁致塑性效应,计算表明主要合金相β(Mg_(17)Al_(12))为顺磁性,有助于发挥磁场作用效果.磁场提高了位错运动灵活性并促使位错增殖,晶界处位错堆积和应力集中促进了再结晶形成,晶粒发生细化,发挥细晶强韧化效果;同时磁场诱发塑性变形时的晶粒转动,新生成非基面取向的晶粒弱化了镁合金(0001)基面织构,该组织特征有助于提高材料的塑变能力.     

Creation and manipulation of coherences in molecules with a pulsed magnetic field

We demonstrate the application of a pulsed magnetic field for the creation and manipulation of coherences in molecular systems, using quantum beat spectroscopy for the detection of the dynamics of the molecular superposition states. In all cases, the experiments are performed on energy levels in electronically excited states of the (jet-cooled) CS₂ molecule populated by a short laser pulse. In the basic experiment, following excitation of initially degenerate Zeeman sublevels under zero field conditions with suitable laser polarization, quantum beats are generated at the moment the magnetic field is switched on, even when the field is delayed by several excited state lifetimes. By quenching of the field, it is shown that the molecule may be “frozen” in any superposition state of the participating sublevels. Using a combination of static and pulsed fields with different orientations, the molecule can be prepared in a more general state, described by coherences among all Zeeman substrates. This is achieved by choosing an appropriate time delay for the switched field, without any change to the geometrical parameters of the experiment such as laser polarization or detection direction. Numerical simulations of these dynamical coherence phenomena have been performed to support assignment and interpretation of the experimental results. Received: 8 April 1998 / Accepted: 3 June 1998     

Theory of stripe domains in magnetic shape memory alloys

The evolution of multivariant patterns in thin plates of magnetic shape memory materials with an applied magnetic field was studied theoretically. A geometrical domain-model is considered composed of straight stripe-like martensite variants with constant internal magnetization (high anisotropy limit) and magnetic domain wall orientation fixed by the twin boundaries. Through integral transforms of the demagnetization energy, the micromagnetic energy is cast into a form convenient for direct numerical evaluation and analytical calculations. The equilibrium geometrical parameters of multivariant patterns with straight and oblique twin boundaries have been derived as functions of the applied field and the material parameters of a plate. It is shown that the oblique multivariant states exist only in plates with thicknesses L larger than a certain critical value L₀. In samples with L<L₀ a magnetic-field-driven transformation occurs directly between single variant states.     

Long-time relaxation of an ordered magnetic structure

In a Mössbauer investigation of the parameters of the hyperfine interactions on Fe⁵⁷ nuclei in the ferromagnetic Tb_0.8Y_0.2Fe₂, we have made the first observation of long-time (days, months) relaxation of an ordered magnetic structure. In this effect the orientation of some moments in a sample changes under the action of a pulsed magnetic field (up to 250 kOe) and then slowly reverts to the initial state by means of gradual decomposition of clusters of the reoriented moments. A theoretical estimate of the relaxation time is made.     

Effect of Magnetic Pulse Processing on the Structure and Magnetic Properties of Ferrites

The effect a pulsed magnetic field has on the crystal structure and macroscopic magnetic parameters of hexagonal ferrites BaFe₁₂O₁₉ and SrFe₁₂O₁₉ are studied. It is shown that changes in the physical properties of ferrites are due to the ordering of cation vacancies on the boundaries of hexagonal and spinel blocks that minimize local distortion of the oxygen polyhedrons. Violation of the collinear ordering of the magnetic moments of iron ions in the nonequivalent positions of SrFe₁₂O₁₉ ferrite is observed, due to the selective localization of such vacancies (and thus violations of the magnetic relationships in Fe–O–Fe).