Transition probabilities of Cr(I) and Cr(II) lines lying between 422 and 485 nm,using emission measurements from a wall stabilized arc

The arc emission method has been employed to measure transition probabilities for two hundred and seventy five lines of Cr(I) (of which thirty-five are blended) and for twenty-six lines of Cr(II) lying between 422 and 484 nm. The spectra were photographed by means of a large grating spectrograph. Plasma diagnostics were carefully performed to obtain accurate values of temperatures.The absolute scale was established for Cr(I) lines using precisely known A_mn-values derived from life-time measurements for the resonance lines; for the Cr(II) lines, our absolute scale is based on accurate measurements for the line at 4242.56 Å. The smallest and largest errors estimated for the A_mn-values are ±10% and ±40%. There is generally good agreement with previous experimental data, although our values sometimes deviate by factor of 2–3 from the calculated estimates.     

A thermodynamic explanation for martensitic phase stability of nanostructured Fe-Ni and Co metallic materials

In order to explain the experimental facts that start temperatures of reverse martensite transformation (A_s) for nanostructured Fe-Ni and Co are lower than those for their coarse-grained counterparts, a thermodynamic model was established in this paper. The thermodynamic analysis shows that the decrease of A_s for nanostructured Fe-Ni and Co can be attributed to the difference of surface free energy for martensite and austenite. The correlation between the decrease of A_s and start temperature of martensitic transformation (M_s) in nanostructured material is further proposed.     

High resolution angle-resolved photoelectron spectrum of CO2, excited with polarized resonance radiation

The He(I) excited and angle-resolved photoelectron spectrum of CO₂ is investigated using a focussing VUV-polarizer. High resolution combined with the additional information given by comparing spectra taken at different angles permits detailed analysis of the vibrational structure. β-values are given for all vibrational components hitherto observed in the photoelectron spectrum of the ≈X, ≈A,≈B and ≈C electronic bands. Single excitations of the v₃ mode with vibrational energies 181 meV in the estate and 279 meV in the ≈B-state are reported. The peak at 360 meV vibrational energy in the (≈C-state is reinterpreted as a single v₃ excitation. The β-values of the most intense peaks are also measured using Ne(I) (16.67 and 16.85 eV), Ne(II) (26.86 and 26.95 eV) and He(II) (40.81) resonance radiations.     

Analytical TEM studies of Nd-Fe-B containing V,Co and Dy

Microstructural changes resulting from the addition of V, Co and Dy to Nd-Fe-B to yield the composition Nd_14.4Dy_1.6Fe₆₇Co₅V₄B₈ have been studied using transmission electron microscopy (TEM). Two types of precipitates ranging in size from ≈ 0.1 μm to several micrometers in diameter were observed embedded in the intergranular Nd-rich region and within the hard magnetic matrix grains. These two types of precipitates were round and lamellar, respectively. They were both borides (V boride and V-Fe boride) as shown by electron energy loss spectroscopy (EELS). TEM diffraction patterns revealed that the lamellar phase could be indexed as an orthorhombic structure with a = 0.291 nm, b = 0.278 nm and c = 0.7837 nm, which is close to VB and has not been reported before in V containing Nd-Fe-B material. The round particles have a tetragonal structure with a = 0.53 nm and b = 0.30 nm, which is similar to that of the V_2-x Fe_xB₂ phase reported previously. Co was found to form Nd₃Co precipitates in the Nd-rich boundary regions. The Co dissolved in the matrix phase is responsible for the increase of Curie temperature ( ≈ 354°C).     

Second- and third-order elastic moduli of Co I

Elastic moduli of Co with A ₁-type structure are calculated using models in which the total energy is presented in the form of the energy of clusters consisting of pairs, triplets, and quadruplets of identical atoms. The irreducible energies of the clusters are assumed to contain two terms: E ∝ ?τ^?6, corresponding to the mutual attraction of the particles, and E ∝ ?τ^?6, corresponding to their mutual repulsion. Here, τ stands for the half-edge of an elementary cell. All 27 types of models expected in accordance with symmetry theory are analyzed. Of these, the 13 that yielded elastic modulus values satisfying the structural stability criteria are selected. The potentials of the selected models are used to predict the rigidity moduli of Co films with an A2-type structure.     

Effect of Substitution of Zr and Pr on magnetic properties of R2Co17(R=Er,Yb)

Magnetic properties (saturation magnetizations, Curie temperatures and anisotropy fields) have been measured for the ternary systems Er₂Co_17-xZr_x and Yb₂Co_17-xZr_x and for the quaternary system Er_2-yPr_yCo_16.4Zr_0.6. Introduction of Zr expands the lattice and diminishes the Curie temperature, both indicating Zr replaces Co. Saturation magnetization is diminished, when Zr replaces Co, more rapidly than simple dilution, suggesting Co d-band filling by electron transfer from Zr. The anisotropy field (H_A) is sharply increased when Co replaces Zr, indicating that both preferential substitution and band structure effects are involved. Replacement of Er by Pr enhances H_A, presumably because of preferential replacement of Er at the 2d site. H_A of 42 kOe (at 295 K) was achieved for Er_1.6Pr_0.4Co_16.4Zr_0.6.     

EPR of Co+2 in Mg(CH3COO)2·4H2O

EPR spectra of the ⁵⁹Co⁺² ion in oriented crystals of Mg(CH₃COO)₂·4H₂O have been measured at 9.4 GHz and a temperature of 4.2 K. The data for each of the two metal ion sites per unit cell are well-described by a spin Hamiltonian for $\text{S =}\text{1}\text{2}\text{, I =}\text{7}\text{2}$ with g_x = 6.13, g_y = 389, g_z = 2.49 and A_x = 0.0193, A_y' = 0.075, A_z' = 0.0032 cm^?1. Only the x-axes of the g- and A-tensors coincide. Orientation of the principal directions relative to the crystal axes has been established for the g- and A-tensors at both sites. They are consistent with the weakly ferromagnetic canted antiferromagnetism found in Co(CH₃COO)₂·4H₂O below T_N ?85mK.     

Magnetic anisotropy of Co/Cu/Co films with indirect exchange coupling

The effect of isothermal annealing on the magnetic anisotropy, bilinear and biquadratic exchange coupling energies, and domain structure of Co/Cu/Co trilayer fiilms with d_Co=6 nm and d_Cu=1.0 and 2.1 nm prepared by magnetron sputtering has been studied. It is shown that, under isothermal annealing, the biquadratic coupling energy decreases by more than an order of magnitude in films with d_Cu=1.0 nm and increases in films with d_Cu=2.1 nm. The fourth-order magnetic anisotropy is shown to be related to the existence of biquadratic exchange energy.     

Perpendicular magnetic anisotropy and thermal stability in Co2FeAl0.5Si0.5/Pt multilayers

Perpendicular magnetic anisotropy (PMA) and thermal stability of Co₂FeAl_0.5Si_0.5 (CFAS)/Pt multilayer structure prepared by dc magnetron sputtering have been studied. It is found that the strength of PMA depends on the thickness of CFAS layer, and the maximum effective thickness of CFAS with PMA is demonstrated to be about 1.5 nm. The interfacial anisotropy energy K _s is estimated to be 0.45 erg/cm², which is larger than those of Co/Pd and Co/Ni multilayers and responsible for the strong PMA of the CFAS/Pt multilayer. The annealing treatments will give rise to the loss of PMA of CFAS/Pt multilayer and has the relatively less influence with large period number N. With the increasing of the period number N, the CFAS/Pt multilayers tend to have wasp-waist-shaped easy-axis hysteresis loops and multidomain structures.     

Type I FA (Rb, Cs) and II FA (Li, Na) tunable laser activities and donor-acceptor properties of O and O at KCl (001) surface: first principle calculations

Type I F_A (Rb⁺, Cs⁺) and II F_A (Li⁺, Na⁺) tunable laser activities, adsorptivity and donor-acceptor properties of O and O⁻ adsorbates at the flat surface of KCl crystal were investigated using an embedded cluster model and ab initio methods of molecular electronic structure calculations. Ion clusters were embedded in a simulated Coulomb field that closely approximates the Madelung field of the host surface, and the nearest neighbor ions to the defect site were allowed to relax to equilibrium. Based on the calculated Stokes shifted optical transition bands, F_A tunable laser activities were found to be inversely proportional to the size of the dopant cation (Li⁺, Na⁺, Rb⁺, Cs⁺) relative to the host cation (K⁺). This relation was explained in terms of the axial perturbation of the impurity cation. The probability of orientational bleaching attributed to the RES saddle point ion configuration along the 〈110〉 axis was found to be inversely proportional to the size of the dopant cation, with activation energy barriers of ca. 0.44-3.34 eV. Surface relaxation energies of type II F_A centers were more important than those of type I F_A centers. In terms of defect formation energies, the products of type II F_A center imperfection were more stable than those of type I F_A. The difference between F or F_A band energies and exciton bands depended almost exclusively on the size of the positive ion species. As far as the adsorptivity of O and O⁻ is concerned, the results confirm that surface imperfection enhances the adsorption energies by ca. 4.38-16.37 eV. O and O⁻ penetrate through the defect-containing surface. The energy gap between the adsorbate and the defect containing surface and the donor-acceptor property of adsorbate play the dominant role in the course of adsorbate substrate interactions and the results were explained in terms of electrostatic potential curves and Mulliken population analysis.     

Cold fragmentation in thermal-neutron-induced fission of 233U and 235U

The mass spectrometer Lohengrin of the Institut Laue-Langevin in Grenoble was used to measure fission-fragment mass yields in the mass range 80 ≤ A ≤ 107 for light-fission-fragment kinetic energies up to about 115 MeV for the reactions ^233,235U(n_th, f). The kinetic energies corresponding to a common fixed yield level for each isobar reflect the influence of the proton pairing energy, but not of the neutron pairing energy. By using calculated Q-values for the different mass splits, mass distributions at fixed total excitation energy are deduced from the data. At a fixed total excitation energy of about 7 MeV, the yield increases from very asymmetric mass splits (A_L ≈ 80) to more symmetric mass splits (A_L ≈ 105) by more than two orders of magnitude. This strong dependence on the mass split seems to be correlated with the decreasing surface-to-surface distance of the unaccelerated fission fragments in this range of mass splits, as calculated under the assumption that the total Q-value is represented by the mutual Coulomb repulsion of the two fragments. The influence of the fission-fragment ground-state deformations on the yield in cold fragmentation could not be detected unambiguously.     

Directional distributions of beta-rays emitted from polarized 60Co nuclei

The ⁶⁰Co nuclei in a thin permendur foil were polarized by a pair of orthogonal magnetic flux loops at ultralow temperatures. The observed angular distribution and the asymmetry factor (A_exp = ?1.01 ± 0.02) are in excellent agreement with theoretical predictions of (1 + α cos θ) dependence and A_theory = ?1.0.     

Impurity in three substitutional locations: Single-crystal EPR study of VO(II) in zinc maleate tetrahydrate

Single-crystal EPR study of VO(II)-doped zinc maleate tetrahydrate has been carried out at room temperature. Four types of impurities have been identified in the single-crystal spectra with intensity ratio of 11:5:2:1. However, the analysis has been done only for the three most intense resonances. The evaluated spin Hamiltonian parameters (A in units of mT) from single-crystal rotations are site I: g_xx=1.981, g_yy=1.971, g_zz=1.939; A_xx=7.43, A_yy=7.70, A_zz=18.7; site II: g_xx=1.973, g_yy=1.966, g_zz=1.939; A_xx=7.08, A_yy=7.22, A_zz=18.5; site III: g_xx=1.978, g_yy=1.977, g_zz=1.951; A_xx=7.11, A_yy=7.32, A_zz=18.3.The powder spectrum gives only one set of g and A values, confirming the presence of only one chemically equivalent site. The paramagnetic impurity, VO(II), has entered the lattice substitutionally for all the three sites. The superhyperfine structure, in the intensity ratio of 1:4:6:4:1, arising from the protons of the water ligands, has been found in one site. The admixture coefficients have been calculated and the complex is found to be fairly covalent in nature.     

Optische Untersuchung der Hyperfeinstruktur einiger La I-Linien und Interpretation der gemessenenA-Faktoren

Several La I transitions were investigated by means of optical interference spectroscopy. AllA-values of the levels of the configuration 5d 6s 6p withJ=9/2, 7/2, and 5/2 were measured. Applying sum rules, the one-electrona-valuea _6s (5d 6s 6p) was derived. It is shown that a promising interpretation of the measuredA-values cannot be done without properly considering core-polarization and configuration interaction with adjacent configurations.     

Control and enhancement of structural and magnetic properties of Co/Pd multilayer by seeded epitaxy

Effects of Co seed layer on the structural and magnetic properties of Co/Pd multilayers have been studied. Reflection high-energy electron diffraction measurements showed a possible control of the crystal orientation of Pd buffer layer from polycrystalline to face-centered cubic (111) orientation when using Co seed layer. Additionally, atomic force microscopy observations confirmed the ability of Co seed layer to flatten the Pd buffer layer drastically. In fact, the usage of Co seed layer has decreased the root-mean-square roughness from 2.3 to 0.23 nm. As for controlling the structural properties of Pd buffer layer, the effective perpendicular magnetic anisotropy constant was enhanced, mainly by the improvement of surface anisotropy. Electronic states of α-Al₂O₃(0001)/metal interface obtained by electron energy loss spectroscopy proved that these differences were the fruit of the interaction between the metal layer and oxygen atoms on the Al₂O₃(0001) surface.     

Jahn-Teller-type phase transitions in oxide ceramics and other solids with Cu(II) — from the viewpoint of a solid state chemist

After a short outline of the vibronic features of the local Jahn-Teller effect (E _g ? ε _g coupling) the cooperative aspects — in particular the various order patterns of the elongated octahedra in Cu(II) solids — are reviewed. While the elastic interactions can be described by energy terms of Q_ε symmetry, the local Jahn-Teller effect has Q_θ symmetry (? = 0). Phase transitions in dependence on the Cu(II) concentration are analysed in detail for oxidic ordered perovskites Ba(Sr)₂Zn(Ni)_1-x Cu_xW(Te)O₆, which exhibit ferrodistortive order patterns connected with first order phase transitions at high x-values. At lower x-values at the short-range order scale elastic Q_ε-type strains prevail as in the cases of antiferrodistortive order, leading to continuous phase transitions. Here, the cluster distribution has been successfully analysed by EPR spectroscopy.     

Growth of nano Co encapsulated in carbon-shell

Nanostructured cobalt is one of the key elements in catalysis and therapeutic drug delivery. To design and prepare nanosize-controllable cobalt, a better understanding of its growth mechanism is essential. Growth of Co nanoparticles encapsulated in carbon-shell (Co@C) during temperature-programmed carbonization of the Co²⁺-β-cyclodextrin (CD) complex at 363–573 K was, therefore, studied by in situ synchrotron small-angel X-ray scattering and X-ray absorption near edge structure spectroscopy. The carbon-shell having a thickness of about 2 nm can prevent the core Co from being aggregated and oxidized. A relatively slow reduction of Co(II) to Co is observed at 393–423 K (stage I) prior to a particle growth transition-state possessing Co of 2.2 nm in diameter at 423–483 K. At 483–513 K (stage II), an increasing Co(II) reduction rate coupled with a rapid fusion and coalescence of Co nanoparticles is found. The average growth rates of Co at stages I and II are about 27 and 98 atoms/min, respectively. The most-probable particle diameter of the ripened Co is 5.9 nm. The carbon-shell can be removed by steam reforming to yield the Co nanoparticles. This work also exemplifies the possible temperature-controllable growth of Co@C, especially in the Co size range of 2–6 nm in diameter.     

Oscillator strengths of neutral and singly ionised molybdenum

Oscillator strengths of 174 Mo(I) and 58 Mo(II) lines in the range 2470–5570 Å were obtained from wall-stabilised arc and hollow cathode measurements. Sets of relative f-values were determined by a combination of hook and emission measurements requiring no assumptions concerning the plasma state. The sets have been enlarged considerably by evaluating spectra recorded with a Fourier spectrometer. The relative Mo(I) f-values were converted to an absolute scale by means of radiative lifetimes measured by P. Zimmermann and his group. The overall uncertainties are within 10–35%. Since lifetimes of Mo(II) levels are not yet available, only relative Mo(II) f-values are presented.     

Lifetime measurements in56Co with the58Ni(d, αγ)56Co reaction

The two-particle pick-up reaction⁵⁸Ni(d, αγ)⁵⁶Co atE _d =7.0 MeV was used to determine mean lifetimes of levels in⁵⁶Co up to 2.73 MeV excitation energy by the Doppler shift attenuation method,γ-rays were observed in a 43 cm³ Ge(Li)-detector at 90° to the beam axis in coincidence withα-particles detected in two 200 μm-silicon surface barrier detectors atΘ _α =±55°. Mean lifetimes for 10 levels in⁵⁶Co and two lifetime limits have been obtained usingF(τ)-curves calculated with the Winterbon theory. The experimental results are compared with the predictions of recent shell model calculations.     

Bias voltage dependence of tunneling magnetoresistance in granular C60–Co films with current-perpendicular-to-plane geometry

Voltage-dependence of the tunneling magnetoresistance effect in the granular C₆₀–Co films has been investigated for the samples with the current-perpendicular-to-plane geometry. The transport measurements under this geometry demonstrate that the granular C₆₀–Co films show an unusual exponential bias voltage dependence of the magnetoresistance ratio down to zero voltage. Small characteristic energies of less than 10's meV are derived from the temperature dependences of the characteristic voltage in the exponential relationship. Considering the magnitudes of the voltage drop between Co nanoparticles and also the effect of cotunneling on the energy values, the characteristic energies for the voltage-induced degradation of the spin polarization are found to show a satisfactory agreement with that for the thermally-induced one. It can be reasonably expected that the onset of magnetic disorder to the localized d-electron spins at the interface region of the C₆₀-based matrix (C₆₀–Co compound) with Co nanoparticles leading to the unusual voltage and temperature dependence of the magnetoresistance ratio and the spin polarization at low temperatures.