Microscopic Magnetism of Nickel-Based Infinite-Layer Superconducting Parent Compounds RNiO_(2)(R=La,Nd):A μSR Study

By using muon spin relaxation(μSR)measurements,we perform a comparative study of the microscopic magnetism in the parent compounds of infinite-layer nickelate superconductors RNiO_(2)(R=La,Nd).In either compound,the zero-fieldμSR spectra down to the lowest measured temperature reveal no long-range magnetic order.In LaNiO_(2),short-range spin correlations appear below T=150 K,and spins fully freeze below T∼10 K.NdNiO_(2)exhibits a more complex spin dynamics driven by the Nd 4f and Ni3d electron spin fluctuations.Further,it shows features suggesting the proximity to a spin-glass state occurring below T=5 K.In both compounds,the spin behavior with temperature is further confirmed by longitudinal-field μSR measurements.These results provide new insight into the magnetism of the parent compounds of the superconducting nickelates,crucial to understanding the microscopic origin of their superconductivity.

极区电离层对IMF Bz4次快速转向的响应--EISCAT／ESR雷达观测

利用EISCAT VHF和EISCAT Svalbard(ESR)雷达观测数据,对2003年2月12日IMF B_z分量4次快速方向转换期间,极区电离层,尤其是极尖/极隙区的响应特征进行了分析研究.随着IMF B_z方向的多次快速变化,地面雷达观测到极尖/极隙区所在位置随着开放闭合磁力线边界在纬度方向上来回移动.在此期间,极区电离层等离子体水平对流多次反向,表现出与IMF B_z分量强的负相关性.进一步分析表明:极区磁层-电离层系统在日侧对IMF极性变化的平均响应时间约为3 min.

钙长石成分熔体粘滞度和自扩散系数压力效应的分子动力学研究

用分子动力学方法,研究了1999 K下,压力由23 MPa上升到15183 MPa的过程中,CaAl_2Si_2O_8成分熔体的微观结构、剪切粘滞度和粒子自扩散系数的压力效应。在此基础上,探讨压力对剪切粘滞度与粒子自扩散系数之间关系的影响,并将它同微观结构的变化联系起来。结果表明,粒子自扩散系数的压力效应与熔体结构有很强的相关性;压力的挤压效应阻碍了粒子的扩散,而Si-O和Al-O 5次配位体的形成又加速了扩散过程,两种相反的作用相互抵消,造成的结果是在0～5 GPa范围内,Si^(4+),O^(2-)和Al^(3+)等网架形成粒子的自扩散系数随压力变化不明显;当压力继续增大时,挤压效应占了主导,导致自扩散系数值快速减小。Ca^(2+)作为网架修饰粒子,自扩散系数随压力升高单调下降。压力小于5 GPa时,粒子自扩散系数的大小关系是:D_(Ca)>D_(Al)>D_O>D_(Si)。系统粘滞度随压力的变化与熔体中BO的含量密切相关:BO含量小于域值时,一定范围内BO含量的变化不会对粘滞度产生很大的影响,超过域值,BO含量的微小增加会导致粘滞度值迅速增大。有效应用Eyring方程的关键是方程中粒子跳跃距离的确定,本研究发现,Si^(4+)和O^(2-)的跳跃距离可以通过系统中非桥氧的百分含量来获得。这一发现使得我们能够利用系统中NBO的含量。

NaAlSi_3O_8熔体粒子扩散行为压力效应的分子动力学研究

为了研究压力对钠长石成分熔体粒子微观扩散行为的影响,本文用分子动力学方法,探讨了2001.5K温度下,压力由50MPa上升到19862 MPa的过程中,熔体的微观结构、粒子自扩散系数随压力的变化规律。研究表明,在升压过程中,低次配位体^(|4|)Al和^(|4|)Si向5次和6次配位体转变,^(|5|)Al的含量在15 GPa达到极大值,而^(|5|)Si含量的极大值在20 GPa仍未出现。Na的自扩散系数随压力升高单调下降,Al、Si和O的自扩散系数随压力升高先增后减,在8～10GPa左右达到极大值,网架形成粒子自扩散系数的极大值与^(|4|)Al和^(|4|)Si含量的极大值对应的压力点不一致。所有粒子的自扩散系数与它们与0之间键的寿命呈线性负相关。

掺杂对ZrO_2中氧扩散行为影响的分子动力学模拟

利用分子动力学软件MOLDY对MgO稳定ZrO2和CaO稳定ZrO2中氧的扩散进行了分子动力学模拟。结果表明,MgO稳定ZrO2和CaO稳定ZrO2中氧的扩散情况很相似,都由温度及MgO或CaO的掺杂量决定,当MgO或CaO的掺杂量适当时氧的扩散系数存在一个最大值;氧的扩散通过空位进行。

Properties of Field Aligned Current in Plasma Sheet Boundary Layers in Magnetotail： Cluster Observation

Field aligned current （FAC） distribution in the plasma sheet boundary layers （PSBLs） in the magnetotail is studied statistically by analysing magnetic field data from the Cluster 4-point measurements. The results show that the FAC distribution on the dusk side is not the same as that on the dawn side in the magnetotail. On the each side earthward and tailward, FA C occurrences are different; occurrence and average current density of FA Cs in the northern hemisphere are different from those in the southern hemisphere. This implies that the FACs have dusk-dawn side asymmetry, polarity asymmetry and inter hemisphere difference in the magnetotail. The present results give a good observation evidence for study on the FAC mechanism.

Conceptual design and update of the 128-channel μSR prototype spectrometer based on musrSim

An experimental muon source(EMuS) will be built at the China Spallation Neutron Source(CSNS). In phase I of CSNS, it has been decided that EMuS will provide a proton beam of 5 kW and 1.6 GeV to generate muon beams. A 128-channel muon spin rotation/relaxation/resonance(μSR) spectrometer is proposed as a prototype surface muon spectrometer in a sub-branch of EMuS. The prototype spectrometer includes a detection system, sample environment, and supporting mechanics. The current design has two rings located at the forward and backward directions of the muon spin with 64 detectors per ring. The simulation shows that the highest asymmetry of approximately 0.28 is achieved by utilizing two 10-mm-thick brass degraders. To obtain the optimal asymmetry, the two-ring structure is updated to a four-ring structure with 32 segments in each ring. An asymmetry of 0.42 is obtained through the simulation, which is higher than that of all the current μSR spectrometers in the world.

CaO稳定氧化锆中氧扩散行为的分子动力学模拟

利用分子动力学软件Moldy对CaO稳定ZrO_2(CSZ)中,Ca非均匀分布情况下氧的扩散行为进行了分子动力学模拟。结果表明,CSZ中氧扩散受控于Ca分布状态,存在氧通过Ca-Ca间隙扩散的情况。富钙区氧扩散系数高于低钙区;径向分布函数表明,在富钙区的Ca在平衡位置附近振幅增大,氧离子通过Ca-Ca间隙进行扩散的几率上升,促进了氧扩散。

Muon Spin Relaxation Study of Frustrated Tm_(3)Sb_(3)Mg_(2)O_(14)with Kagomé Lattice

The structure and magnetic properties of rare-earth ions Tm^(3+)Kagomé lattice Tm_(3)Sb_(3)Mg_(2)O_(14)are studied by x-ray diffraction,magnetic susceptibility and muon spin relaxation(𝜇SR)experiments.The existence of a small amount of Tm/Mg site-mixing disorder is revealed.DC magnetic susceptibility measurement shows that Tm^(3+)magnetic moments are antiferromagnetically correlated with a negative Curie-Weiss temperature of−26.3 K.Neither long-range magnetic order nor spin-glass transition is observed by DC and AC magnetic susceptibility,and confirmed by μSR experiment down to 0.1 K.However,the emergence of short-range magnetic order is indicated by the zero-field μSR experiments,and the absence of spin dynamics at low temperatures is evidenced by the longitudinal-field μSR technique.Compared with the results of Tm_(3)Sb_(3)Zn_(2)O_(14),another Tm-based Kagomé lattice with much more site-mixing disorder,the gapless spin liquid like behaviors in Tm_(3)Sb_(3)Zn_(2)O_(14)can be induced by disorder effect.Samples with perfect geometrical frustration are in urgent demand to establish whether QSL exists in this kind of materials with rare-earth Kagomé lattice.

A Critical Review of the Evidence for M32 being a Compact Dwarf Satellite of M31 rather than a More Distant Normal Galaxy

Since Baade＇s photographic study of M32 in the mid 1940s, it has been accepted as an established fact that M32 is a compact dwarf satellite of M31. The purpose of this paper is to report on the findings of our investigation into the nature of the existing evidence. We find that the case for M32 being a satellite of M31 rests upon Hubble Space Telescope （HST） based stellar population studies which have resolved red-giant branch （RGB） and red clump stars in M32 as well as other nearby galaxies. Taken in isolation, this recent evidence could be considered to be conclusive in favour of the existing view. However, the conventional scenario does not explain M32＇s anomalously high central velocity dispersion for a dwarf galaxy （several times that of either NGC 147, NGC 185 or NGC 205） or existing planetary nebula observations （which suggest that M32 is more than twice as distant as M31） and also requires an elaborate physical explanation for M32＇s inferred compactness. Conversely, we find that the case for M32 being a normal galaxy, of the order of three times as distant as M31, is supported by： （1） a central velocity dispersion typical of intermediate galaxies, （2） the published planetary nebula observations, and （3） known scaling relationships for normal early-type galaxies. However, this novel scenario cannot account for the high apparent luminosities of the RGB stars resolved in the M32 direction by HST observations. We are therefore left with two apparently irreconcilable scenarios, only one of which can be correct, but both of which suffer from potentially fatal evidence to the contrary.This suggests that current understanding of some relevant fields is still very far from adequate.

Superconductivity in the Layered Cage Compound Ba_(3)Rh_(4)Ge_(16)

We report the synthesis and superconducting properties of a layered cage compound Ba_(3)Rh_(4)Ge_(16).Similar to Ba_(3)Ir_(4)Ge_(16),the compound is composed of 2 D networks of cage units,formed by noncubic Rh-Ge building blocks,in marked contrast to the reported rattling compounds.The electrical resistivity,magnetization,specific heat capacity,andμSR measurements unveiled moderately coupled s-wave superconductivity with a critical temperature T_(c)=7.0 K,the upper critical field μ_(0)H_(c2)(0)~2.5 T,the electron-phonon coupling strength λ_(e-ph)~0.80,and the Ginzburg-Landau parameterκ~7.89.The mass reduction with the substitution of Ir by Rh is believed to be responsible for the enhancement of T_(c) and coupling between the cage and guest atoms.Our results highlight the importance of atomic weight of framework in cage compounds in controlling the λ_(e-ph) strength and T_(c).

Magneto-Elastic Coupling in a Sinusoidal Modulated Magnet Cr_(2)GaN

We use neutron powder diffraction to investigate the magnetic and crystalline structure of Cr_(2)GaN.A magnetic phase transition is identified at T≈170 K,whereas no trace of structural transition is observed down to 6 K.Combining Rietveld refinement with irreducible representations,the spin configuration of Cr ions in Cr_(2)GaN is depicted as an incommensurate sinusoidal modulated structure characterized by a propagating vector k=(0.365,0.365,0).Upon warming up to the paramagnetic state,the magnetic order parameter closely resembles to the temperature dependence of c-axis lattice parameter,suggesting strong magneto-elastic coupling in this compound.Therefore,Cr_(2)Ga N provides a potential platform for exploration of magnetically tuned properties such as magnetoelectric,magnetostrictive and magnetocaloric effects,as well as their applications.

Insensitivity of a turbulent laser-plasma dynamo to initial conditions

It has recently been demonstrated experimentally that a turbulent plasma created by the collision of two inhomogeneous,asymmetric,weakly magnetized,laser-produced plasma jets can generate strong stochastic magnetic fields via the small-scale turbulent dynamo mechanism,provided the magnetic Reynolds number of the plasma is sufficiently large.In this paper,we compare such a plasma with one arising from two pre-magnetized plasma jets whose creation is identical save for the addition of a strong external magnetic field imposed by a pulsed magnetic field generator.We investigate the differences between the two turbulent systems using a Thomson-scattering diagnostic,x-ray selfemission imaging,and proton radiography.The Thomson-scattering spectra and x-ray images suggest that the external magnetic field has a limited effect on the plasma dynamics in the experiment.Although the external magnetic field induces collimation of the flows in the colliding plasma jets and although the initial strengths of the magnetic fields arising from the interaction between the colliding jets are significantly larger as a result of the external field,the energies and morphologies of the stochastic magnetic fields post-amplification are indistinguishable.We conclude that,for turbulent laser-plasmas with supercritical magnetic Reynolds numbers,the dynamo-amplified magnetic fields are determined by the turbulent dynamics rather than the seed fields or modest changes in the initial flow dynamics of the plasma,a finding consistent with theoretical expectations and simulations of turbulent dynamos.

Magnetic Phase Diagram of Cu4-xZnx(OH)6FBr Studied by Neutron-Diffraction and μSR Techniques

We systematically investigate the magnetic properties of Cu4-xZnx(OH)6FBr using the neutron diffraction and muon spin rotation and relaxation(μSR) techniques.Neutron-diffraction measurements suggest that the longrange magnetic order and the orthorhombic nuclear structure in the x=0 sample can persist up to x=0.23 and 0.43,respectively.The temperature dependence of the zero-field μSR spectra provides two characteristic temperatures,TA0 and Tλ,which are associated with the initial drop close to zero time and the long-time exponential decay of the muon relaxation,respectively.Comparison between TA0 and TM from previously reported magnetic-susceptibility measurements suggest that the former comes from the short-range interlayer-spin clusters that persist up to x=0.82.On the other hand,the doping level where Tλ becomes zero is about 0.66,which is much higher than threshold of the long-range order,i.e.,~0.4.Our results suggest that the change in the nuclear structure may alter the spin dynamics of the kagome layers and a gapped quantum-spin-liquid state may exist above x=0.66 with the perfect kagome planes.

用灰阶编码掩模实现邻近效应精细校正的研究

提出了用灰阶编码的二元掩模代替灰阶掩模实现邻近效应精细校正的新方法 ,并阐述了新方法的特点。讨论了灰阶编码掩模与灰阶掩模的等效关系 ,给出了灰阶编码掩模实现光学邻近效应校正的模拟结果 ,校正后的综合面积偏差比校正前减少了 10 %。

使用二元相位菲涅尔波带片产生轴向线聚焦

介绍了一种全新的轴向线聚焦方案 .采用菲涅尔波带片 ,在实验中产生了沿轴向长为 5mm ,宽 10 0 μm的线聚焦 .光学测量表明 ,线聚焦轴向强度分布比较均匀 .这些参数基本上可以满足激光等离子体实验的要求 .

数值模拟辐射场对激光等离子体中物理过程的影响

利用研究非局域热力学平衡态下等离子体的程序包NIMP ,就辐射场对等离子体中的激发和离化过程的影响进行了数值模拟研究 。

TC-1卫星在近地磁尾(9～13 R_E)探测到的对流型高速流和场向高速流

对2004～2006年期间每年的6～11月(2006年截止到10月),共17个月的TC-1卫星上4s精度的FGM和HIA数据进行了统计分析.统计结果显示:在区域(-14RE<X<-9RE,|Y|<10RE,|Z|<5RE)内,TC-1卫星共观测到的高速流事件共465起,其中对流型高速流94起,场向流型事件371起.对流型高速流和场向高速流有明显不同,主要表现在:对流型高速流流场和磁场夹角超过45°,Bx磁场强度小于15nT较弱,β的最可几值为0.4;场向高速流流场和磁场夹角的最可几值为20°,Bx磁场强度的最可几值约为30nT,β的最可几值0.1.对流型高速流主要发生在等离子体片内;场向高速流主要分布在等离子体片边界层附近.TC-1卫星的观测结果表明,近地对流型高速流与爆发性整体高速流(bursty bulk flows,BBFs)的特性一致,说明有相当数量的BBFs是可以进入近地13RE以内的.由于对流型高速流能够更有效的向近地磁尾输运能量,有可能会对亚暴触发过程产生重要的影响.

IMF Bz多次快速反向期间极尖区的Cluster观测

2003年2月12日,ACE卫星观测到IMFBz分量的4次快速反向：从稳定的北向（Bz～9nT）快速转为稳定的南向（Bz～-8nT）;在持续南向约34min后Bz再次转为稳定北向（Bz－5nT）；约22min后，ACE卫星观测到南向的IMF；IMF保持南向约46min后第二次转回稳定的北向（Bz－6nT）．

不同高度处极尖区位置对地磁偶极倾角的依赖程度

由于太阳风与地球磁层相互作用以及地磁偶极倾角的存在,地球磁层极尖区的位置在不断变化.这种变化不仅与太阳风参数的扰动变化有关,而且与地磁偶极轴运动状态有关.关于极尖区位置对地磁偶极倾角的依赖程度问题,