Goldanskii-Karyagin asymmetry in Fe3(CO)12

The Mössbauer effect spectra of Fe₃(CO)₁₂ have been measured from 4.2 to 295 K and reveal an unusual temperature dependence in the relative area of the two components of the quadrupole doublet associated with the two equivalent iron sites and in the relative area of the two observed quadrupole doublets. The asymmetry in the outer quadrupole doublet is attributed to the Goldanskii-Karyagin effect. The strong temperature dependence of the relative areas of the two quadrupole doublets results from a differing temperature dependence of the recoil free fractions for the two chemically different sites.     

钡钇氟化物中Eu2+离子的激发光谱和发射光谱

在298和77K下分别研究BaYF5(BaF2·YF3)中Eu2+的激发和发射光谱。Eu2+的发射光谱中,除了一个属5d-4f跃迁的宽发射带外,还有一组6PJ→8S7/2的4f-4f跃迁窄谱线发射。它们的发射强度与Eu2+的浓度和温度有关。由於Eu2+从4f7基态跃迁到4f65d1态产生两个宽的激发带,4f65d(eg)和4f65d(t2g)。实验证实,Eu2+的6PJ→8S7/2的窄谱线发射主要来自高能级的t2g激发能弛豫的结果。     

Mössbauer study on Fe-sitting site and origin of magnetic order in YBa2(Cu0.95Fe0.05)3O7−δ

Fe-sitting sites and the origin of magnetic order in YBa₂(Cu_0.95Fe_0.05)₃O_7?δ have been studied by comparing the Mössbauer spectra observed before and after heat-treatments at 300°C in vacuum. Both of the major quadrupole doublets D-1 and D-2 are assigned to originate from Fe’s replacing Cu1’s. It is also suggested that fluctuations of Cu2 spins play an important role for inducing the magnetic order.     

Electron–Nuclear Spin Dynamics in Semiconductor QDs

This work presents an overview of investigations of the nuclear spin dynamics in nanostructures with negatively charged InGaAs/GaAs quantum dots characterized by strong quadrupole splitting of nuclear spin sublevels. The main method of the investigations is the experimental measurements and the theoretical analysis of the photoluminescence polarization as a function of the transverse magnetic field (effect Hanle). The dependence of the Hanle curve profile on the temporal protocol of optical excitation is examined. Experimental data are analyzed using an original approach based on separate consideration of behavior of the longitudinal and transverse components of the nuclear polarization. The rise and decay times of each component of the nuclear polarization and their dependence on transverse magnetic field strength are determined. To study the role of the Knight field in the dynamic of nuclear polarization, a weak additional magnetic field parallel to the optical axis is used. We have found that, only taking into account the nuclear spin fluctuations, we can accurately describe the measured Hanle curves and evaluate the parameters of the electron–nuclear spin system in the studied quantum dots. A new effect of the resonant optical pumping of nuclear spin polarization in an ensemble of the singly charged (In,Ga)As/GaAs quantum dots subjected to a transverse magnetic field is discussed. Nuclear spin resonances for all isotopes in the quantum dots are detected in that way. In particular, transitions between the states split off from the ±1/2 doublets by the nuclear quadrupole interaction are identified.     

2,6-吡啶二甲酸镝配位聚合物的合成、晶体结构及其发光性能研究

以2,6-吡啶二甲酸为配体,在水热条件下合成出一个具有(4.82)拓扑结构的二维稀土镝配位聚合物[Dy(PDA)(HPDA)]n(1)(H2PDA=2,6-吡啶二甲酸).通过元素分析,1H NMR,IR和X射线单晶衍射对其进行结构表征.X射线单晶衍射分析结果表明,该化合物届单斜晶系,P2(1)/c空间群.该化合物由配体的氧原子连接,形成具有(4.82)型拓扑的二维层状结构,相邻层间的π-π堆积弱相互作用使之形成三维超分子.测定了配体和1在固态室温条件的紫外吸收和荧光光谱.在室温下,配体和配合物均在280 nm处有一宽谱带强吸收,这可以归属于以配体为中心的π→π*跃迁.当激发波长为280 nm时,1呈现出基于配体为中心的荧光发射峰和稀土Dy3+的特征荧光发射峰.研究了配位聚合物1的固态荧光寿命,荧光衰减过程包含双组分,相应的荧光寿命τ1和τ2分别是3.61和12.81μs.     

ESEEM Measurements of Local Water Concentration in D<Subscript>2</Subscript>O-Containing Spin-Labeled Systems

To calibrate electron spin echo envelope modulation (ESEEM) amplitudes with respect to the deuterium water content in spin-labeled biological systems, ESEEM of nitroxide TEMPO has been studied in frozen glassy D₂O-dimethylsulfoxide mixtures of different composition. The interaction between the unpaired electron of nitroxide and the deuterium nuclei manifests itself in a cosine Fourier transform spectrum as the sum of a narrow line with the doublet quadrupole splitting and of a broad one. The narrow line arises from interaction with distant deuterium nuclei, the broad one arises from interaction with nearby nuclei belonging to nitroxide-water molecule complexes. The dependence on water concentration was found to be nonlinear for the intensity of the narrow line and close to linear for the intensity of the quadrupole doublet. Therefore, the intensity of the quadrupole doublet is suggested as a measure of concentration of free water around a spin label in biological objects. Fourier transform line shape was theoretically simulated for different model distributions of water molecules around the spin label. Simulations confirm the linear dependence of the quadrupole doublet intensity on water concentration seen in the experiment. The suggested approach was applied to analyze data for spin-labeled dipalmitoylphosphatidylcholine (DPPC) and DPPC-cholesterol D₂O-hydrated model membranes. The concentration of free water near the spin-labeled fourth carbon atom along the lipid chain was estimated as 5.2 and 7.2 M for DPPC and DPPC-cholesterol membranes, respectively. Authors’ address: Sergei Dzuba, Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, Institutskaya 3, 630090 Novosibirsk, Russian Federation     

晶态四硼酸锶中二价镝的发射

在室温下测量了在空气中灼烧掺杂Dy2O3的SrB3O7的发射光谱。观测到了由Dy^3 到Dy^2 氧化态的变化。经优化,当在空气中灼烧温度为650℃时为产生Dy^2 的最佳温度。在457．9nm的激发下测出了两个峰位分别位于550和660nm的宽发射带。我们认为这两个宽发射带是由Dy^2 离子由5d态向4f基态能级（^5I8）跃迁产生的。讨论了几个有益于在这种基质中还原Dy^3 离子的条件。为了实现Dy^3 离子的还原,我们还在Ar/H2(4%)气氛中制备了Dy2O3掺杂的SrB4O7比较了这种样品和在空气中所制备的样品的光学特性。本文还对标专SrB4O7还原性和稳定性的g－因子由Tm^2 的[E0(Tm^3 /Tm^2 =-2.3V]推导出Dy^2 的[E0(Dy^3 /Dy^2 )=-2.6V],但对这种还原过程的局限性尚未确定。     

The hyperfine structure and hyperfine anomaly of 161Dy and 163Dy

The hyperfine structure of ¹⁶¹Dy and ¹⁶³Dy for five transitions hasbeen measured with a tunable dye laser and a thermal velocity atomic beam. Values for the magnetic dipole and electric quadrupole coupling constants have been determined for the relevant excited states. The hyperfine anomaly parameters, Δ, which are extracted are interpreted in terms of available atomic wave functions.     

Quadrupole interactions and relaxation effects in Dy2Ti2O7

Studies of quadrupole interactions and relaxation phenomena in Dy₂Ti₂O₇ at various temperatures up to 750 K have been performed using the Mössbauer effect of the 25.6 keV transition in ¹⁶¹Dy. The source used was ¹⁶¹Tb in ¹⁶⁰Gd₂Ti₂O₇ at 150 K, which emits a very narrow 25.6 keV γ line. Quadrupole interaction parameters and relaxation times, as function of temperature, were deduced from the measurements.     

Multivariate analysis in provenance studies: Cerrillos obsidians case, Peru

We present the preliminary results of a provenance study of obsidians samples from Cerrillos (ca. 800–100 b.c.) using Mössbauer Spectroscopy. The Cerrillos archaeological site, located in the Upper Ica Valley, Peru, is the only Paracas ceremonial center excavated so far. The archaeological data collected suggest the existence of a complex social and economic organization on the south coast of Peru. Provenance research of obsidian provides valuable information about the selection of lithic resources by our ancestors and eventually about the existence of communication routes and exchange networks. We characterized 18 obsidian artifacts samples by Mössbauer spectroscopy from Cerrillos. The spectra, recorded at room temperature using different velocities, are mainly composed of broad asymmetric doublets due to the superposition of at least two quadrupole doublets corresponding to Fe²⁺ in two different sites (species A and B), one weak Fe³⁺ doublet (specie C) and magnetic components associated to the presence of small particles of magnetite. Multivariate statistical analysis of the Mössbauer data (hyperfine parameters) allows to defined two main groups of obsidians, reflecting different geographical origins.     

Systematic Mössbauer study of YBa2Cu3−x Fe x Oδ and PrBa2Cu3−x Fe x Oδ as a function of temperature

We study the similitudes and differences between YBa₂Cu_3?x Fe _x O_δ and PrBa₂Cu_3?x Fe _x O_δ systems, using Mössbauer spectroscopy. Both systems, withz=0.04, were studied at several temperatures. The spectra of PrBa₂Cu_3?x Fe _x O_δ showed four asymmetric quadrupole doublets with apparently different line widths, which were fitted with four symmetric superimposed quadrupole doublets with the same line width, but assuming a small (～4–6 kOe) residual magnetic field in the Fe sites, which are mainly the Cu(1) sites of the 1–2–3 structure. On the other hand, the PrBa₂Cu_3?x Fe _x O_δ spectra showed only three asymmetric quadrupole doublets which can be fitted with three superimposed symmetric doublets and a residual magnetic field. In this case, the Fe atoms also occupy the Cu(1) sites of the 1–2–3 structure. The temperature variations of the Mössbauer spectra and their parameters seem to indicate that, in the Pr-system, a structural change takes place between 12 K and 40 K.     

Mössbauer study on M1 and M2 sites of Fe2+ in natural hypersthene under dynamic crystal field potential approach

⁵⁷Fe Mössbauer spectra of hypersthene, a natural silicate mineral belonging to the orthopyroxene group, have been taken over the temperature range 77–292 K. At temperatures above 77 K, they show asymmetric quadrupole peaks. This asymmetry arises from the overlapping of two quadrupole doublets from Fe²⁺(3d⁶,⁵D) ions in two different sites (M1 and M2). The quadrupole splitting, isomer shift and their temperature dependence are appreciably different for Fe²⁺ ions in the two sites. The Fe²⁺ quadrupole splitting in the M1 site decreases linearly with temperature, which can be explained quite satisfactorily by using a very simple model of the orbit-lattice interaction.     

Spin-lattice interaction in the quasi-one-dimensional helimagnet LiCu2O2

The field dependence of the electron spin resonance in a helimagnet LiCu2O2 was investigated for the first time. In the paramagnetic state, a broad resonance line was observed corresponding to a g factor of 2.3. In the critical regime, around the paramagnetic to helimagnetic phase transition the resonance broadens and shifts to higher frequencies. A narrow signal is recovered at a low temperature, corresponding to a spin gap of 1.4 meV in zero field. A comprehensive model of the magnons is presented, using exchange parameters from neutron scattering [T. Masuda Phys. Rev. B 72, 014405 (2005)10.1103/PhysRevB.72.014405] and the spin anisotropy determined here. The role of the quantum fluctuations is discussed.     

Evidence of anomalous multiplet line shapes in optically thick,laser-produced plasmas

We report observations of anomalous line shapes for the transitions 2p?3d (²P?²D) emitted by the Li-like ions N(V), O(VI), F(VII) in laser-produced plasmas. These transitions are normally doublets but show completely different characteristics (e.g., triplet structures or invension of two-component intensity ratios) in the plasmas. The observed line profiles are accounted for in terms of opacity and Doppler effect produced by plasma expansion. This interpretation is independent of the particular transition involved, i.e., multiplet structures can generate more complicated features with various unexpected new components, anomalous intensity ratios, etc.     

Nuclear magnetic moment of161Tb

Nuclear orientation measurements on dilute TbGd are analysed to yield the magnetic dipole and electric quadrupole moments of¹⁶¹Tb g.s. and multipole mixing ratios of transitions in¹⁶¹Dy.     

SrTiO3 displacive transition revisited via coherent X-ray diffraction

We present a coherent x-ray diffraction study of the antiferrodistortive displacive transition of SrTiO3, a prototypical example of a phase transition for which the critical fluctuations exhibit two length scales and two time scales. From the microbeam x-ray coherent diffraction patterns, we show that the broad (short-length scale) and the narrow (long-length scale) components can be spatially disentangled, due to 100-microm-scale spatial variations of the latter. Moreover, both components exhibit a speckle pattern, which is static on a approximately 10 mn time scale. This gives evidence that the narrow component corresponds to static ordered domains. We interpret the speckles in the broad component as due to a very slow dynamical process, corresponding to the well-known central peak seen in inelastic neutron scattering.     

2H chemical shift anisotropies from high-field 2H MAS NMR spectroscopy

2H chemical shift anisotropies (CSAs) have been determined for the first time for polycrystalline samples employing 2H MAS NMR spectroscopy at high magnetic field strength (14.1 T). The 2H CSA is reflected as distinct asymmetries in the manifold of spinning sidebands (ssbs) observed for the two overlapping single-quantum transitions. Least-squares fitting to the manifold of ssbs allows determination of the 2H CSA parameters along with the quadrupole coupling parameters. This is demonstrated for KD2PO4, ND4D2PO4, KDSO4, KDCO3, alpha-(COOD)2, alpha-(COOD)2.2D2O, and boehmite (AlOOD) which exhibit 2H shift anisotropies in the range 13< or =deltasigma< or =27 ppm. For fixed values of the shift anisotropy and the 2H quadrupole coupling it is shown that the precision of the CSA parameters depends strongly on the asymmetry parameter (etaQ) for the quadrupole coupling tensor, giving the highest precision for etaQ approximately 0. The 2H CSA parameters (deltasigma and etasigma) are in good agreement with 1H CSA data reported in the literature for the corresponding protonated samples from 1H NMR spectra employing various homonuclear decoupling techniques. The determination of 2H quadrupole coupling parameters and 2H (1H) CSAs from the same 2H MAS NMR experiment may be particularly useful in studies of hydrogen bonding since the 2H quadrupole coupling constant and the CSA appear to characterize bond lengths in a hydrogen bond in a different manner.     

Binding Strength and Oxygen Coordination of the Fe Sites in High TC GdBa2 Cu3O7—δ

The GdBa₂(Cu_1－xFe_x)₃O_7—δ system with x=0.005－0.001 and various oxygen concentrations was investigated by ⁵⁷Fe-Mossbauer spectroscopy in temperature range 20K to 300K.The spectra of the orthorhombic phase were analyzed with four quadrupole doublets.Three of them were attributed to substitutional Cu(1) sites and one (with the smallest quadrupole splitting)to the substitutional Cu(2) site.From an analysis of temperature dependence of the relative site intensities,different local Debye temperature for the Cu(1) sites were derived.Highly texturized absorbers were investigated to study the polarization dependence of the four quadrupole doublets.Measurements at the magic angle gave evidence for a vibrational anisotropy (Goldanskii-Karyagineffect) of the Cu(1) sites.The Cu(1) site with the largest quadrupole splitting exhibited the lowest Debye temperature and the largest vibrational anisotropy.     

Observation of intrinsic excitation in 160Dy following heavy-ion transfer reactions

The population of sidebands in ¹⁶⁰Dy has been observed following the ¹⁶¹Dy(⁵⁸Ni, ⁵⁹Ni) ¹⁶⁰Dy reaction. The intensity of discrete transitions in these bands, identified using particle-γ−γ coincidence measurements, was found to be weak compared to the ground-state band. A peak of width 500–600 keV at about 1 MeV, observed in the NaI spectra, is attributed to the decay of two- quasiparticle states to the ground-state band. A second peak at 400–500 keV is attributed to transitions between 2-quasiparticle states.     

A CEMS study of ac-axis oriented thin film of YBa2(Cu0.97 57Fe0.03)3O7

⁵⁷Fe Mössbauer spectra of a fullyc-axis oriented epitaxial thin film of YBa₂(Cu_0.97 ⁵⁷Fe_0.03)₃O₇, recorded by CEMS, are reported. Spectra taken at different angles between the normal of the film (i.e. thec-axis) and the gamma ray direction show that for two of the three observed quadrupole doublets the main component of the EFG lies in thea?b-plane, for the third doublet it is parallel to thec-axis. The EFG of all three doublets has approximately axial symmetry.