Anomalous spontaneous reversal in magnetic heterostructures

We observe a thermally induced spontaneous magnetization reversal of epitaxial ferromagnet/antiferromagnet heterostructures under a constant applied magnetic field. Unlike any other magnetic system, the magnetization spontaneously reverses, aligning antiparallel to an applied field with decreasing temperature. We show that this unusual phenomenon is caused by the interfacial antiferromagnetic coupling overcoming the Zeeman energy of the ferromagnet. A significant temperature hysteresis exists, whose height and width can be tuned by the field applied during thermal cycling. The hysteresis originates from the intrinsic magnetic anisotropy in the system. The observation of this phenomenon leads to open questions in the general understanding of magnetic heterostructures. Moreover, this shows that in general heterogeneous nanostructured materials may exhibit unexpected phenomena absent in the bulk.     

飞秒激光与等离子体相互作用中自生磁场的热电机制

采用理论分析和数值模拟研究了考虑相对论效应的自生磁场及其产生机制,给出了自生磁场的解析表达式,得到了温度梯度和密度梯度的非共线性所引起的自生磁场空间分布的时间演化关系。数值结果表明,当峰值强度为1019 W/cm2的激光作用于凹形靶前表面时,在等离子体表面领域观察到的自生磁场最大值为51102 T量级,与实验测量结果相符合。     

飞秒激光与等离子体相互作用中自生磁场的热电机制

采用理论分析和数值模拟研究了考虑相对论效应的自生磁场及其产生机制,给出了自生磁场的解析表达式,得到了温度梯度和密度梯度的非共线性所引起的自生磁场空间分布的时间演化关系。数值结果表明,当峰值强度为1019 W/cm2的激光作用于凹形靶前表面时,在等离子体表面领域观察到的自生磁场最大值为51102 T量级,与实验测量结果相符合。     

Effect of a periodic magnetic field on phase matching condition in second harmonic generation at interactions of laser-plasma

In this paper, the process of second harmonic generation (SHG) is studied in underdense plasma in the presence of a periodic magnetic field. It is shown that the difference of momentums of photon of second harmonic and two photons of main wave can be provided by momentum of everyone of Fourier components of periodic magnetic field so that momentum of nth Fourier component can be chosen by . It is also proven that the highest efficiency of second harmonic generation will be provided by the first Fourier component of periodic magnetic field . It is revealed that periodic magnetic field can produce longitudinal waves at and as well.     

Solitons in relativistic laser-plasma interactions

Single or/and multipeak solitons in plasma under relativistic electromagnetic field are reviewed. The incident electromagnetic field is allowed to have a zero or/and nonzero initial constant amplitude. Some interesting numerical results are obtained that include a high-number multipeak laser pulse and single or/and low-number multipeak plasma wake structures. It is also shown that there exists a combination of soliton and oscillation waves for plasma wake field. Also, the electron density exhibits multi-caviton structure or the combination of caviton and oscillation. A complete eigenvalue spectrum of parameters is given wherein some higher peak numbers of multipeak electromagnetic solitons in the plasma are included. Moreover, some interesting scaling laws are presented for field energy via numerical approaches. Some implications of results are discussed.      

Anomalous behavior of textures in a magnetic field

It is shown that a qualitatively new type of transition to a nonlinear phase is possible in two-dimensional two-phase textures in a magnetic field. The anomalous growth of the effective response (higher-order correlation functions of the current) near the critical magnetic field is studied. The dependence of the critical magnetic field on the angles of microinclusions is calculated. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 2, 115–119 (25 July 1997)     

On self-induced transparency in laser-plasma interactions

We study fully relativistic nonlinear one-dimensional equations describing steady-state solutions for an electromagnetic wave interacting with a plasma in the self-induced transparency regime. In addition to the well-known solution that corresponds to the transmission of the electromagnetic wave into plasma, another steady-state solution is shown to exist in a certain range of amplitudes of the wave. The latter solution corresponds to total reflection of the incident wave. The coexistence of the two solutions indicates the possibility of hysteretic behavior in the self-induced transparency. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 7, 445–450 (10 October 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Photon kinetics for laser-plasma interactions

A photon kinetic formalism is employed to describe the propagation of short laser pulses in tenuous plasmas. The photon kinetic theory contains all of the ingredients necessary to describe the relativistic nonlinear optics of short laser pulses in plasmas, and the shortest time scale is determined by the local evolution of the index of refraction. We use this feature to implement a photon in cell code, in which the typical time step is much bigger than is the laser field time scale. Additional information provided by the photon kinetic framework is illustrated by one-dimensional (1-D) and two-dimensional (2-D) simulations     

Proton shock acceleration in laser-plasma interactions

The formation of strong, high Mach number (2-3), electrostatic shocks by laser pulses incident on overdense plasma slabs is observed in one- and two-dimensional particle-in-cell simulations, for a wide range of intensities, pulse durations, target thicknesses, and densities. The shocks propagate undisturbed across the plasma, accelerating the ions (protons). For a dimensionless field strength parameter a(0)=16 (Ilambda(2) approximately 3 x 10(20) W cm(-2) microm(2), where I is the intensity and lambda the wavelength), and target thicknesses of a few microns, the shock is responsible for the highest energy protons. A plateau in the ion spectrum provides a direct signature for shock acceleration.     

Anomalous currents in dense matter under a magnetic field

We consider fermionic dense matter under a magnetic field, where fermions couple minimally to gauge fields, and calculate anomalous currents at one loop. We find anomalous currents are spontaneously generated along the magnetic field but fermions only in the lowest Landau level contribute to anomalous currents. We then show that there are no more corrections to the anomalous currents from two or higher loops.     

Electro-optic shocks from ultraintense laser-plasma interactions

Second harmonic radiation in the form of an electro-optic shock is produced in the blowout regime of a laser wakefield in a plasma. The shock is produced by the interaction between the laser field and the electron sheath surrounding the electron cavitation region. Because the sheath is thin, phase matching is unimportant, and the radiated energy grows secularly with the interaction length. The angle of emission is given by the Cherenkov angle associated with the ratio of the second harmonic phase velocity to the fundamental phase velocity. The shock formation is investigated in three dimensions via analysis and particle-in-cell simulations.     

Anomalous absorption of ultrasound in gadolinium in a magnetic field

The absorption coefficient α _k for longitudinal ultrasonic (15 MHz) waves propagating transverse to the direction of a magnetic field H is measured in single crystal gadolinium. It is found that in fields H⩽600 Oe, the peak in α _k is shifted toward lower temperatures, while the absolute magnitude of the absorption rises with increasing H. It is shown on the basis of dynamic scaling that the anomalous behavior of α _k in fields H⩽600 Oe can be explained by introducing a magnetic field analog of the Landau-Khalatnikov relaxation mechanism. Fiz. Tverd. Tela (St. Petersburg) 39, 339–340 (February 1997)     

Anomalous properties of 2-D electrons in a magnetic field

In strong magnetic field and at low temperature, 2-D electron systems are expected to show distinctive temperature oscillations when the field is changed adiabatically.     

利用韧致辐射诊断激光等离子体相互作用产生的超热电子

超短脉冲强激光与等离子体相互作用时产生的向靶内传输的超热电子在“快点火”方案中起着极其重要的作用.对于这部分向靶内传输的超热电子，韧致辐射方法是一种能有效、全面获得超热电子各方面信息的诊断方法.通过三维蒙特卡罗程序MCNP模拟了超热电子在靶材料中的输运以及它们在靶后方向产生的韧致辐射的性质，论证了韧致辐射诊断方法的可行性. 关键词： 超热电子 韧致辐射 诊断 MCNP程序     

Magnetization reversal of small particles in an oscillating magnetic field

The nonlinear behavior of single spherical particles and many-particle ensembles under an external oscillating magnetic field was studied using the Landau-Lifshitz-Gilbert approach. The exact analytical formulae for calculating field frequency and the dependence of the configuration of the initial moment on the system mean magnetization were obtained. Using asymptotic decomposition we obtained simple expressions for describing the nonlinear dynamics of spherical particles in the cases of large and small frequencies. These solutions are in good agreement with numerical calculations of the Landau-Lifshitz-Gilbert equation for the considering systems.