Phase Transitions of Fel2 in high magnetic field parallel to the spin direction,static field up to 150 kOe,pulsed field up to 250 kOe

Study of parallel and perpendicular susceptibilities shows that ferrous iodide presents at low temperature an antiferromagnetic order, with spins oriented along the anisotropy axis (c axis).Phase transitions of Fel₂ in a magnetic field parallel to c axis are studied by help of magnetization measurements. At low temperature (2.2 K) saturation is reached only for a magnetic field of 140 kOe. Results obtained in high static fields (Bitter and supraconductive coils allowing respectively 140 and 150 kOe) and in pulsed field are presented.At low temperature, two successive first order phase transitions are observed at 46 and 120 kOe. In the intermediate phase, the magnetization presents two minor discontinuities. An original phase diagram is given.The complexity of the Fel₂ behavior, in parallel magnetic field shows that the magnetic structure is not the same as the two sublattices one characteristic of FeCl₂ and FeBr₂. An estimate of the principal exchange coupling parameters and a study by neutron diffraction measurements (to be published) confirm an original magnetic structure.     

A terahertz gyrotron with pulsed magnetic field

We present the results of first experiments with a small-size gyrotron on the basis of a pulsed solenoid with a magnetic field of about 40 T. The generation of microwave radiation in the frequency range from 0.9 to 1.02 THz is obtained. The pulse duration is about 40 µs for a kilowatt power level. The microwave pulse repetition rate is limited by the solenoid cooling capability and is about 1 pulse per minute, which is an order of magnitude higher than that in known foreign analogs.     

A submillimeter gyrotron with a pulsed magnetic field

Pulse solenoids seem promising for sumbillimeter wave generation in gyrotrons. In this paper a single-pulse submillimeter gyrotron with a pulsed magnetic field is described. At the wavelength 0.8 mm the output power 120 KW with the efficiency 15% has been obtained.     

A germanium oscillator in a pulsed magnetic field

Experimental data which confirms the presence of hysteresis of the magnetic threshold field of the helical instability of the plasma in a germanium oscillator are presented. It is shown that hysteresis of the threshold magnetic field is due to the inertia of the change in the effective lifetime of the charge carriers in the specimen when the magnetic field is increased and reduced. The dependence of the hysteresis of the threshold magnetic field on the electric field strength, the magnetic field, and the temperature is discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 38–41, July, 1982.The authors thank R. I. Bashirov, and K. M. Aliev for making it possible to carry out the measurements in pulsed magnetic fields, and G. P. Il'yukevich for his technical help.     

NMR in pulsed magnetic field

Nuclear magnetic resonance (NMR) experiments in pulsed magnetic fields up to 30.4 T focused on ¹H and ⁹³Nb nuclei are reported. Here we discuss the advantage and limitation of pulsed field NMR and why this technique is able to become a promising research tool.     

脉冲强磁场下的电极化测量系统

多铁性材料是当前物质科学研究的热点,具有重要的科学研究意义和应用前景.低温和强磁场实验环境为研究多铁性材料提供了一种有效途径.脉冲强磁场下的电极化测量系统能实现最高磁场强度60 T、最低温度0.5 K的铁电特性测量.该系统采用热释电方法,具有磁场强度高、控温范围广、转角测量等特点,可用于强磁场下的磁电特性研究.本文介绍了该系统的测量装置和实验原理,并展示了其在多铁性材料研究中的一系列应用,揭示了脉冲强磁场电极化测量系统在磁电特性探索中的重要作用.     

微型计算机在脉冲磁场作用下的效应试验

 介绍了脉冲强磁场模拟器的工作原理, 将微型计算机置于脉冲磁场模拟器中，通过改变脉冲磁场的幅度和上升时间，研究脉冲磁场对微电子设备的干扰途径、干扰阈值与脉冲上升时间、脉冲宽度的关系。试验结果表明，微电子设备的连接电缆是脉冲磁场干扰引入的主要途径；简单的屏蔽措施对于脉冲磁场干扰有一定的抑制作用；脉冲磁场的时间变化率越大，对微电子设备的干扰作用越强。     

微型计算机在脉冲磁场作用下的效应试验

介绍了脉冲强磁场模拟器的工作原理, 将微型计算机置于脉冲磁场模拟器中,通过改变脉冲磁场的幅度和上升时间,研究脉冲磁场对微电子设备的干扰途径、干扰阈值与脉冲上升时间、脉冲宽度的关系。试验结果表明,微电子设备的连接电缆是脉冲磁场干扰引入的主要途径;简单的屏蔽措施对于脉冲磁场干扰有一定的抑制作用;脉冲磁场的时间变化率越大,对微电子设备的干扰作用越强。     

对称脉冲强磁场发生器的研制

 对称脉冲强磁场发生器是一台能够产生周期为10 μs左右的强磁场装置,由10 μF的脉冲电容作为储能系统,平板传输线、电缆和气体开关作为传输系统,单匝线圈作为负载。为了使两个对称布置的负载能同时工作,设计了一个能同时输出8路脉冲信号的同步触发系统,其时间分散性约为20 ns。在常温常压下,当储能电容和同步触发系统分别加压到28 kV和49 kV并且气体开关工作气压为80 kPa时,线圈中心最大磁感应强度约为18 T。     

脉冲磁场下金属熔体凝固流场的数值模拟

用ANSYS55有限元数值模拟软件对铝合金熔体凝固过程中的流场作了数值模拟，模拟结果和实验现象相符合.通过数值模拟发现，用数值模拟的方法不仅可以初步了解凝固过程中熔体的流动状态，而且可以了解凝固组织细化和产生缺陷的原因.因此，是一个值得注意的研究方向，有较大的实用价值.     

Dynamic triggering of a spin-transition by a pulsed magnetic field

We report the first study of the effect of a high pulsed magnetic field on a spin transition complex in the solid state. The high spin fraction was determined by optical reflectivity. Sizeable effects are observed for the well-known spin transition solid Fe(Phen)₂(NCS)₂. In the hysteresis loop temperature range, an increase in the HS fraction is obtained, with an irreversible (reversible) character in the ascending (descending) branch of the loop. The time dependence of the HS fraction provides information on the kinetics of the spin-crossover process at the spin transition. Received 23 February 1999 and Received in final form 8 June 1999     

Activation of a semiconductor surface by a pulsed magnetic field

The possibility of semiconductor surface activation, which shows up as a long-term increase in the adsorption capacity in response to a short exposure to a pulsed magnetic field, is demonstrated for the first time. Magnetic-field-induced surface activation is studied on silicon, germanium, and gallium arsenide crystals. The effect revealed extends the capabilities of thin-film growth on the semiconductor surface.     

铁基非晶的低频脉冲磁场处理效应

对非晶合金Fe₇₈ Si₉ B₁₃进行了低频脉冲磁场处理，用穆斯堡尔谱学、透射电 镜等方法观察处理试样的微观结构变化.研究发现，当脉冲频率20—25Hz,磁场16—32kA/m,作用时间≤2min，合金发生了纳米晶化，纳米相岐睩e(Si)晶粒尺寸为10nm. 而且，在低频脉冲磁场处理过程中，非晶试样的温升≤20℃. 关键词： 非晶态合金 脉冲磁场处理 纳米晶化     

Application of pulsed high magnetic field to μSR studies

The technical development in the production of pulsed high magnetic field to be used for μSR studies is described. A pulsed field up to 16 T with half-sine wave shape and 1 msec duration is repeated every 2 sec and the muon beam pulses are synchronized at the peak of the field. Paramagnetic relaxation measurement on MnO has been performed at above 10 T as a test of this equipment and relaxation in PrCo₂Si₂ has been studied in the vicinity of the metamagnetic transition at 12 T at He temperature.     

Surface temperature evolution in pulsed laser action of millisecond range

An originally developed multi-wavelength pyrometer (12 wavelengths in the range 1.001-1.573 μm, 50 μs acquisition time for each photodiode, 800 μm spatial resolution, 900-3500 °C brightness temperature range) is used to measure brightness temperature under the pulsed action of Nd:YAG laser (HAAS-HL62P) on stainless steel (INOX 304L) substrates. Specially developed “notch” filters (10⁻⁶ transparency at 1.06 μm wavelength) are applied to avoid the influence of laser radiation on temperature measurements. The true temperature is restored on the basis of method of multi-colour pyrometry. The accuracy of brightness temperature measurements is examined by comparing the temperature evolution for pulses with different durations but with the same value of energy density flux.The influence of the following parameters is studied keeping the remaining ones constant: pulse duration (6-20 ms, rectangular pulse shape), energy per pulse (10-33 J, rectangular pulse shape), pulse shape (three types of triangulars and one rectangular). Finally the evolution of surface temperature for pulses with more complex shapes but with the same pulse duration and energy per pulse is compared.     

脉冲磁场下水热法制备Cr掺杂ZnO稀磁 半导体晶体

本文以ZnCl₂, CrCl₃. 6H₂O和氨水缓冲溶液为原料, 在4T脉冲磁场下水热法制备了Cr掺杂ZnO稀磁半导体晶体, 通过X射线衍射分析、扫描电子显微镜观察及采用振动样品磁强计进行磁性分析等, 探讨了脉冲磁场对其微观结构及磁性能的影响. 结果表明: Cr掺杂ZnO稀磁半导体晶体仍保持ZnO的六方纤锌矿结构, 脉冲磁场具有促进晶粒生长及取向排列的作用, 4T脉冲磁场条件下合成的Cr掺杂ZnO稀磁半导体具有良好的室温铁磁性, 其饱和磁化强度(M_s)为0.068 emu/g, 而无脉冲磁场情况下制备的样品室温下呈顺磁性, 并且, 脉冲磁场下制备将稀磁半导体的居里温度提高了16 K.     

Modelling the unsteady melt flow under a pulsed magnetic field

A numerical model for the unsteady flow under a pulsed magnetic field of a solenoid is developed, in which magnetohydrodynamic flow equations decouple into a transient magnetic diffusion equation and unsteady Navier–Stokes equations in conjunction with two equations of the k–ε turbulent model. A Fourier series method is used to implement the boundary condition of magnetic flux density under multiple periods of a pulsed magnetic field （PMF）. The numerical results are compared with the theoretical or experimental results to validate the model under a time-harmonic magnetic field; it is found that the toroidal vortex pair is the dominating structure within the melt flow under a PMF. The velocity field of a molten melt is in a quasi-steady state after several periods; changing the direction of the electromagnetic force causes the vibration of the melt surface under a PMF.     

Dynamics of cylindrical conducting shells in a pulsed longitudinal magnetic field

A theoretical model is constructed for describing the motion of a cylindrical conducting shell in a pulsed longitudinal magnetic field generated by an external solenoid. The model takes into account the dynamics of the electric circuit (with the solenoid as its part), inertial and strength properties of the shell, magnetic field diffusion, and heating of the solenoid and shell materials. Difference schemes are constructed for the numerical solution of the system of the defining differential equations, and the criteria of their stability are analyzed. The model is used for studying magnetic-p ulse compression of hollow shells, as well as magnetic field compression in their inner cavity, and the effect of controlling parameters such as the starting charge voltage of the energy storage system and the size of the shell being compressed on the process dynamics is analyzed. Various approximations for calculating the shell heating (adiabatic approximation and uniform heating approximation) are analyzed in comparison with rigorous calculations. The possibility of conducting shell expansion due to magnetic field diffusion into the inner cavity is investigated.