掺有Ni2+的α-Al2O3晶体的基态精细光谱、晶体局域结构和Jahn-Teller效应

应用晶体场理论和不可约张量算符方法构造了3d2/3d8态离子在C3v对称晶场中包含自旋-轨道相互作用、自旋-自旋相互作用、自旋-其它轨道相互作用和其它轨道-其它轨道相互作用四种微观磁效应的45阶可完全对角化的能量哈密顿矩阵.利用该矩阵,计算了Ni2+∶α-Al2O3晶体的光谱精细结构和晶体局域结构,深入研究了Ni2+∶α-Al2O3晶体的自旋-轨道相互作用、自旋-自旋相互作用、自旋-其它轨道相互作用和其它轨道-其它轨道相互作用和它们对光谱精细结构的影响及Jahn-Teller效应.理论计算值和实验值相符合.研究发现,掺杂没有改变晶体的对称性、同时发现并合理解释了Ni2+对α-Al2O3晶体基态精细光谱中Jahn-Teller效应的存在机理.     

Magnetic properties of hole-doped SCGO, SrCr(8)Ga(4-x)M(x)O(19) (M?=?Zn, Mg, Cu)

We report changes in the magnetic properties of hole-doped SCGO, SrCr8Ga4O19, induced by replacing non-magnetic Ga3+ with both non-magnetic (Mg2+ and Zn2+) and magnetic (Cu2+) cations. The resulting solid solutions, SrCr(8)Ga(4-x)M(x)O(19) (M = Zn, Mg, Cu) have been studied by x-ray diffraction and magnetic susceptibility measurements. For all cases, at least 10% of Ga can be replaced by divalent cations resulting in oxidation of ≥5% of the Cr3+ d3 to Cr4+ (d2). The hole doping results in an increase in ferromagnetic interactions and reduces the magnetic frustration. In the SrCr(8)Ga(4-x)Cu(x)O(19) series an enhancement of the spin-glass-like transition is observed, T(f)～ 6 K, which we ascribe to the magnetic nature of the Cu2+ (d9) dopant.     

铁基超导体Fe1+yTe1-xSex中磁性的中子散射研究

本文对本研究组主要的研究领域——利用中子散射研究铁基超导体系Fe_1+yTe_1-xSe_x中磁性与超导的相互作用进行简要综述. Fe_1+yTe_1-xSe_x具有和其他铁基、铜基超导体相似的相图——母相Fe_1+yTe是反铁磁体, 随着Se掺杂的增加, 母相的反铁磁序受到抑制, 随后在x～30%处体超导出现, 在x～50%处达到最佳掺杂, 此时超导转变温度T_c～ 15 K, 达到整个体系在常压下的T_c最大值. 它们的相图又存在着差别: 在相图末端, 即当Se掺杂达100%时, Fe_1+ySe 仍然超导, T_c～8 K. 该体系母相磁有序的面内波矢大致为(0.5,0) (采用每个原胞含2个铁原子的四方结构), 随着Se含量的增加, 在超导逐渐发展的同时, 磁激发谱的谱重被逐渐转移到波矢为(0.5,0.5) 处. (0.5,0.5) 处在温度低于T_c 时出现中子-自旋共振峰. 施加外磁场后, 超导受到抑制, 该共振峰也被压制. 从这些实验结果我们得到以下的结论: 在这个体系中磁性和超导紧密耦合在一起——(0.5,0) 处的静态磁有序与超导互相竞争, (0.5,0.5) 附近的自旋激发则可能对超导电性的形成具有重要的促进作用. 本文还将简要讨论磁性的来源和3d 过渡金属的替代效应.     

The splitting of hyperfine lines of57Fe nuclei in RF magnetic field

It is shown experimentally, that for Moessbauer nuclei affected by the radio-frequency (RF) magnetic field of sufficient intensity at frequencies corresponding to NMR, splitting of Zeeman sublevels of nuclei and changes in Moessbauer spectral structure occurs. Depending on the frequency of alternating field each spectral line is splitinto (2·Ig,e +1) comporients, Ig,e-being the nuclear spin of ground and excited state, respectively. The intensity of RF components and the energy gap between them are extremely sensitive to the frequency and the intensity of the RF magnetic field.     

Effect of a magnetic field on transit time of excited atoms in a dc arc plasma

Transit times of excited atoms in a dc arc plasma exposed to an inhomogeneous magnetic field are investigated at different values of the magnetic induction. At the optimal value, the transit time, electron pressure and spectral line intensities are maxima. The large increase of spectral line intensity is not proportional to the slight increase of transit time. The transit times of different atoms at the same value of the magnetic induction are approximately equal, whereas the spectral line intensities are different. The maximum transit time corresponds to minimum electron mobility. The arc-plasma temperature is directly proportional to the magnetic induction.     

Calculation of magnetic exchange interactions in Mott-Hubbard systems

An efficient method of computing magnetic exchange interactions in systems with strong correlations is introduced. It is based on a magnetic force theorem that evaluates linear response due to rotations of magnetic moments and uses a generalized spectral density functional framework allowing us to explore several approximations ranging from local density functional to exact diagonalization based dynamical mean field theory. Applications to spin waves and magnetic transition temperatures of 3d metal mono-oxides as well as high-T(c) superconductors are in good agreement with experiment.     

Hidden magnetic configuration in epitaxial La(1-x) Sr(x) MnO3 films

We present an unreported magnetic configuration in epitaxial La(1-x) Sr(x) MnO3 (x ～ 0.3) (LSMO) films grown on strontium titanate (STO). X-ray magnetic circular dichroism indicates that the remanent magnetic state of thick LSMO films is opposite to the direction of the applied magnetic field. Spectroscopic and scattering measurements reveal that the average Mn valence varies from mixed Mn(3+)/Mn(4+) to an enriched Mn3+ region near the STO interface, resulting in a compressive lattice along the a, b axis and a possible electronic reconstruction in the Mn e(g) orbital (d(3)z(2)-r(2). This reconstruction may provide a mechanism for coupling the Mn3+ moments antiferromagnetically along the surface normal direction, and in turn may lead to the observed reversed magnetic configuration.     

Electronic structure of charge- and spin-controlled Sr(1-(x+y))La(x+y)Ti(1-x)Cr(x)O3

We present the electronic structure of Sr(1-(x+y))La(x+y)Ti(1-x)Cr(x)O3 investigated by high-resolution photoemission spectroscopy. In the vicinity of the Fermi level, it was found that the electronic structure was composed of a Cr 3d local state with the t(2g)3 configuration and a Ti 3d itinerant state. The energy levels of these Cr and Ti 3d states are well interpreted by the difference of the charge-transfer energy of both ions. The spectral weight of the Cr 3d state is completely proportional to the spin concentration x irrespective of the carrier concentration y, indicating that the spin density can be controlled by x as desired. In contrast, the spectral weight of the Ti 3d state is not proportional to y, depending on the amount of Cr doping.     

Determination of the gradient magnetic field above a sunspot based on observations of the HeI and FeI infrared lines

The magnetic field strength above 36 sunspots was studied using the spectra of the HeI λ 1083.030 nm and FeI 1082.837 nm magnetosensitive lines. The value of the field was determined directly by Zeeman splitting of the lines. The advantages of our observations are as follows: (a) in the IR region, the Zeeman splitting exceeds the similar splitting in the visible region by several times, (b) both studied lines are in the same spectrum in close proximity to each other, (c) the instrumental scattering in the IR region is lower, d) the measurements are conducted close to the true continuum of intensity between the spectral lines. The relationship between magnetic field strength and residual intensity in both spectral lines is nonlinear. The gradient of the magnetic field above sunspots at heights from the photosphere to the upper chromosphere varies within 0.1–0.7 G/km for all the studied sunspots.     

Structural, magnetic and electronic structure studies of Mn doped TiO2 thin films

We report structural, magnetic and electronic structure study of Mn doped TiO₂ thin films grown using pulsed laser deposition method. The films were characterized using X-ray diffraction (XRD), dc magnetization, X-ray magnetic circular dichroism (XMCD) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy measurements. XRD results indicate that films exhibit single phase nature with rutile structure and exclude the secondary phase related to Mn metal cluster or any oxide phase of Mn. Magnetization studies reveal that both the films (3% and 5% Mn doped TiO₂) exhibit room temperature ferromagnetism and saturation magnetization increases with increase in concentration of Mn doping. The spectral features of XMCD at Mn L_3,2 edge show that Mn²⁺ ions contribute to the ferromagnetism. NEXAFS spectra measured at O K edge show a strong hybridization between Mn, Ti 3d and O 2p orbitals. NEXAFS spectra measured at Mn and Ti L_3,2 edge show that Mn exist in +2 valence state, whereas, Ti is in +4 state in Mn doped TiO₂ films.     

Double photoionization into double core-hole states in Xe

Double photoionization (DPI) leading to double core-hole states of Xe2+ 4d(-2) has been studied using a magnetic bottle time-of-flight spectrometer. The assignments of the Xe2+ 4d(-2) states are confirmed by the Auger lines extracted from fourfold coincidences including two photoelectrons and two Auger electrons. It is estimated that the core-core DPI into Xe2+ 4d(-2) at a photon energy of 301.6 eV has a favored cross section of about 0.3 MB. The intense core-core DPI is due to mixing of the 4d(-2) continuum with the 4p single photoionization, which is manifested in the relative intensities of the Xe2+ 4d(-2) components.     

Eigenfunction entropy and spectral compressibility for critical random matrix ensembles

Based on numerical and perturbation series arguments we conjecture that for certain critical random matrix models the information dimension of eigenfunctions D(1) and the spectral compressibility χ are related by the simple equation χ+D(1)/d=1, where d is system dimensionality.     

掺入Ni2+和V3+对α-Al2O3晶体光谱精细结构、晶体局域结构和零场分裂参量的影响

应用晶体场理论和不可约张量算符方法构造了3d2/3d8态离子在C3v对称晶场中包含自旋-轨道相互作用、自旋-自旋相互作用、自旋-其它轨道相互作用和其它轨道-其它轨道相互作用四种微观磁效应的45阶可完全对角化的能量哈密顿矩阵.利用该矩阵,计算了V³⁺∶α-Al₂O₃和Ni²⁺∶α-Al₂O₃晶体的光谱精细结构、晶体局域结构和零场分裂参量,研究了掺入两种互补态离子Ni²⁺和V³⁺对同种晶体的光谱精细结构、晶体局域结构和零场分裂参量的影响,理论计算值和实验值相符.研究发现：掺杂没有改变晶体的光谱精细结构和能级分裂条数,但改变了能级间距|掺杂也没有改变晶体的对称性,但使晶体局域结构发生了一定程度的畸变| Ni²⁺∶α-Al₂O₃晶体局域结构的伸长畸变量大于V³⁺∶α-Al₂O₃晶体,键角的变化量小于V³⁺∶α-Al₂O₃晶体.     

Spatial chemical inhomogeneity and local electronic structure of Mn-doped Ge ferromagnetic semiconductors

We have investigated the chemical distributions and the local electronic structure of potential diluted magnetic semiconductor Ge0.94Mn0.06 single crystals using scanning photoelectron microscopy (SPEM), x-ray absorption spectroscopy (XAS), and photoemission spectroscopy (PES). The SPEM image shows the stripe-shaped microstructures, which arise from the chemical phase separation between the Mn-rich and Mn-depleted phases. The Mn 2p XAS shows that the Mn ions in the Mn-rich region are in the divalent high-spin Mn2+ states but that they do not form metallic Mn clusters. The Mn 3d PES spectrum exhibits a peak centered at approximately 4 eV below E(F) and the negligible spectral weight near E(F). This study suggests that the observed ferromagnetism in Ge1-xMnx arises from the phase-separated Mn-rich phase.     

Centrality dependence of charged-hadron transverse-momentum spectra in d+Au collisions at sqrt[s(NN)]=200 GeV

We have measured transverse momentum distributions of charged hadrons produced in d+Au collisions at sqrt[s(NN)]=200 GeV. The spectra were obtained for transverse momenta 0.25相似文献   

Pseudo-Zeeman splitting of excited states in MnI2: Cu+

MnI₂ doped with CuI shows extra absorption lines in the spectral region between 24000 and 30000 cm^-1. At low temperature these lines have an anomalously large Zeeman splitting in an applied magnetic field, with apparent g values as large as 150. This effect is attributed to exchange coupling of an electron (or hole) in the excited state with the spins of the surrounding Mn²⁺ ions. The applied magnetic field partly aligns the Mn²⁺ ion spins and this causes the observed very large pseudo-Zeeman splitting of the absorption lines.     

Bosonic spectral density of epitaxial thin-film La1.83Sr0.17CuO4 superconductors from infrared conductivity measurements

We use optical spectroscopy to investigate the excitations responsible for the structure in the optical self-energy of thin epitaxial films of La(1.83)Sr(0.17)CuO(4). Using Eliashberg's formalism to invert the optical spectra we extract the electron-boson spectral function and find that at low temperature it has a two component structure closely matching the spin excitation spectrum recently measured by magnetic neutron scattering. We contrast the temperature evolution of the spectral density and the two-peak behavior in La(2-Sr(x)CuO(4) with another high temperature superconductor Bi(2)Sr(2)CaCu(2)O(8+delta). The bosonic spectral functions of the two materials account for the low T(c) of LSCO as compared to Bi-2212.     

Isovector magnetic dipole sum rules in (d s)- shell

Linear-energy weighted sum-rules (LEWSR) are calculated for isovector magnetic dipole transitions from the ground state in some (d s)-shell nuclei. It is found that the well-known Kurath sum rule is inadequate to explain the experimental transition strengths in these nuclei. A significant contribution to the sum-rule is seen to arise from the two-body part of the Hamiltonian. The calculations are made using the spectral distribution methods.     

Peculiar ferrimagnetism associated with charge order in layered perovskite GdBaMn2O5.0

The magnetic properties of GdBaMn2O5.0, which exhibits charge ordering, are studied from 2 to 400 K using single crystals. In a small magnetic field applied along the easy axis, the magnetization M shows a temperature-induced reversal which is sometimes found in ferrimagnets. In a large magnetic field, on the other hand, a sharp change in the slope of M(T) coming from an unusual turnabout of the magnetization of the Mn sublattices is observed. Those observations are essentially explained by a molecular field theory which highlights the role of delicate magnetic interactions between Gd3+ ions and the antiferromagnetically coupled Mn2+/Mn3+ sublattices.     

水热法与固相法制备Ca2B5O9Cl:Eu光谱特性的研究

对比研究了制备方法(水热法与高温固相法)、激发条件、Eu离子浓度对Ca2B5O9Cl:Eu发光体光谱特性及制备条件对晶体形貌的影响.结果表明,水热法制备的Ca2B5O9Cl:Eu发光体在254 nm激发下主要以Eu3 的5D0→7FJ(J=1,2,3,4)跃迁发射为主,365 nm激发下则以Eu2 的4f65d1→8S7/2跃迁发射为主.高温固相法制备的发光体在365 nm激发下主要是Eu2 的4f65d1→8S7/2跃迁发射,而254 nm激发下Eu2 和Eu3 的发射均较弱.Eu浓度对Ca2B5O9Cl : Eu的光谱特性影响较小,而制备方法和激发条件却对其影响较大.SEM揭示了空气条件与还原气氛制备的产品结晶完美、表面光滑、颗粒度在0.82～1.06 μm之间.