Structure of cobalt nanoparticles as studied by X-ray absorption spectroscopy

Ab initio modeling is used to analyze the specific near-edge features of the X-ray absorption K spectra of ∼3-nm cobalt nanoparticles. It is established that the observed differences between the spectra of the nanoparticles and those of bulk cobalt samples are due to contribution from atoms of the nanoparticles’ surface layer, the local environment of which is considerably different from that of atoms in the bulk of the nanoparticle. It is also established that the local environment of cobalt atoms in the nanoparticle bulk corresponds to the FCC structure of bulk metal, and the fraction of such atoms is found to be 65 ± 5%.     

Spin excitations in a K0.84Fe1.99Se2 superconductor as studied by MSssbauer spectroscopy

Mossbauer spectroscopy was used to probe the site-specific information of a K0.84Fe1.99Se2 superconductor. A spin excitation gap, △E≈5.5 meV, is observed by analyzing the temperature dependence of the hyperfine magnetic field （HMF） at the iron site within the spin wave theory. Using the simple model suggested in the literature, the temperature dependence of the HMF is well reproduced, suggesting that, below room temperature, the alkali metal intercalated iron selenide superconductors can be regarded as ferromagnetically coupled spin blocks that interact with each other antiferromagnetically to form the observed checkerboard-like magnetic structure.     

Oxidation of ZrAl and Zr3Al compounds studied by181Ta-PAC spectroscopy

Hyperfine Interactions - The perturbed angular correlation method was applied to follow the oxidation processes in ZrAl and Zr3Al intermetallic compounds. It was found that the limiting temperature...     

Structure and rotational dynamics of methyl propionate studied by microwave spectroscopy

We report on the rotational spectra of the most abundant conformer of methyl propionate, CH₃CH₂COOCH₃, recorded with a Fourier transform microwave spectrometer under molecular beam conditions. We present accurate rotational constants and centrifugal distortion constants. For the propionyl CH₃ CH₂CO– methyl group and the methoxy –OCH₃ methyl group, barriers of 820.46(99)?cm^?1 and 429.324(23)?cm^?1, respectively, were found. For spectral analysis, two different computer programs were used, the code BELGI-C_s-2tops based on the rho axis method (RAM) and the code XIAM based on the combined axis method (CAM). The results are compared. The experimental work was supplemented by quantum chemical calculations. Potential energy functions for the rotation of the terminal methyl groups and also of the entire ethyl group were parametrized.     

The ferromagnetic to paramagnetic phase transition of Fe studied by x-ray photoelectron spectroscopy

Valence band x-ray photoelectron spectra from Fe(100) have been measured as a function of temperature to above the Curie temperature, T_c. The room temperature data can be reconciled with the theoretical one-particle density of states (DOS). At T = 1.034T_c, the data do not resemble the paramgnetic DOS of Fe as calculated in the disordered-local-moment limit.     

Thermodynamic properties of Fe-Ni solid solutions studied by Fe Mössbauer spectroscopy

The room temperature Mössbauer spectra of ⁵⁷Fe were measured for Ni_1−xFe_x solid solutions with x in the range 0.01≤x≤0.10. The obtained data were analysed in terms of short range order parameter (SRO) and the binding energy E_b between two iron atoms in the studied materials using the extended Hrynkiewicz-Królas idea. It was found that the binding energy is positive or Fe atoms interact repulsively. The extrapolated value of E_b for x=0 was used for computation of enthalpy of solution of Fe in Ni. Finally the values of enthalpies of solution were used to predict the mixing enthalpy curve for the Fe-Ni solid solutions. The results were compared with corresponding value given in the literature, which was calculated theoretically using DFT techniques, as well as with the value obtained from experimental calorimetric data and resulting from the cellular atomic model of alloys by Miedema.     

Interface magnetism of Fe/Nd multilayers studied by Mössbauer spectroscopy

Fe/Nd multilayers with⁵⁷Fe enriched interfaces are prepared to investigate crystal structure and magnetism at the interface by Mössbauer spectroscopy. The intermixture at the interface is less than two atomic layers. The magnetic moments of interface Fe atoms align collinear and turn at a certain temperature or at a certain magnetic field with keeping the collinear structure. By annealing, the interface component with smaller hyperfine field decreases and the perpendicular magnetic anisotropy increases.     

Ionic interactions in solutions of electrolytes as studied by ultra-violet spectroscopy

Spectrophotometric evidence for the formation of contact ion-pairs in solutions of tetra-alkylammonium iodides in certain solvents of poor ion-solvating power, such as carbon tetrachloride, is presented.

Since the band ascribed to contact ion-pairs is not detected for solutions in other solvents, such as chloroform, it is concluded that the ion-pairs detectable by other techniques in such solvents are separated by solvent molecules.     

Magnetic order in LaEuSrCuO studied [2pt] by Fe Mössbauer spectroscopy

⁵⁷Fe M?ssbauer effect studies of La_1.65Eu_0.20Sr_0.15CuO₄ doped with 0.5 at% ⁵⁷Fe performed in the temperature region 300 K > T > 4.2 K give an onset temperature for magnetic ordering of K. This temperature practically is the same as that found in Nd doped La_2-xSr_xCuO₄. It indicates that the magnetic ordering temperature in the LTT phase of rare earth (RE) doped La_2-xSr_xCuO₄ is independent of the RE moment. The direction of the ⁵⁷Fe magnetic moment in the magnetically ordered state is within the CuO₂ plane, while it has been found to be parallel to the c-axis in Nd doped La_2-xSr_xCuO₄. Received: 23 June 1998 / Accepted: 14 July 1998     

Vibrational entropy of dislocations in Al

The region nearest to a lattice defect must be described by an atomistic model, while a continuum model suffices further away from the defect. We study such a separation into two regions for an edge dislocation. In particular we focus on the excess defect energy and vibrational entropy, when the dislocation core is described by a cluster of about 500–100?atoms, embedded in a large discrete and relaxed, but static, lattice. The interaction between the atoms is given by a potential of the embedded-atom model type referring to Al. The dynamic matrix of the vibrations in the cluster is fully diagonalized. The excess entropy ΔS near the core has positive and negative contributions, depending on the sign of the local strain. Typically, ΔS/k _B ≈ 2 per atomic repeat length along the dislocation core in fcc Al. In the elastic continuum region far from the dislocation core the excess entropy shows the same logarithmic divergence as the elastic energy. Although the work refers to a specific material and defect type, the results are of a generic nature.     

Magnetic interaction in Tm3Fe5O12 studied by means of169Tm and57Fe Mössbauer spectroscopy

The temperature dependence of the hyperfine parameters of thulium iron garnet (Tm₃Fe₅O₁₂) powder was studied from 90 to 550 K using¹⁶⁹Tm and⁵⁷Fe Mössbauer spectroscopy (MB). The spectra were analyzed by least mean square fits to the transmission function. The temperature dependence of the magnetic fields of the thulium nuclei is well described by the mean field model. The coupling constants between the magnetic lattice occupied by the thulium atoms and the magnetic lattices occupied by the iron atoms were derived.     

Spinodal decomposition of Fe−Cr−Ni alloys studied by Mössbauer spectroscopy

Summary A thermodynamic calculation of the Fe−Cr−Ni phase diagram suggests that the composition 30 at.%Cr-5 at.%Ni is expected to be found inside the spinodal line, whereas 16 at.%Cr-5 at.%Ni is expected outside at 723 K. These two alloys have been thermally aged for time periods up to 40 minutes at 723K. A significant broadening of the magnetic-hyperfine-field distribution indicates that Fe-30 at.%Cr-5 at.%Ni undergoes typical spinodal decomposition in agreement with the calculation. Spinodal decomposition is distinguished from nucleation-growth by a detailed analysis of the magnetic-hyperfine-field distribution. Paper presented at ICAME-95, Rimini, 10–16 September 1995     

Structure of dichlorine monoxide as studied by microwave spectroscopy. Determination of equilibrium structure by a modified mass dependence method

The microwave spectra of four isotopic species of dichlorine monoxide (OCl₂) have been observed, and the rotational constants have been obtained. The r_m structure for each isotopic species has been determined by Watson's method. The equilibrium structure has been estimated by taking proper averages of r_m structures to be $\text{r}{}_{\mathrm{e}}\text{(OCl) = 1.69587(7)}\text{A}\text{?}$ and ∠_eClOCl = 110.886(6)°. The general applicability and the merit of the present method for estimating the equilibrium structure are pointed out.