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  • 1
    Electronic Resource
    Electronic Resource
    Crystal field analysis and Monte Carlo simulation of lattice disordering for Cm3+ in YPO4 and LuPO4 (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 373-382 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method of analyzing inhomogeneous line broadening with crystal-field theory is presented. For actinide ions with unfilled f-shells in solids, the most important contribution to line broadening of f-electron transitions is from short-range interactions with distorted lattice. Optically active curium ions are used to measure the degree of radiation damage in the vicinity of their lattice site. The radiation damage was produced by decay of distant 244Cm3+ ions. Fluorescence line narrowing (FLN) spectra show that inhomogeneous line broadening induced by α-decay of the actinide ion 244Cm3+ in single crystals of LuPO4 and YPO4 has a microscopic nature. Namely, correlation is absent between energy levels of the Cm3+ ions at different local environments. Monte Carlo simulation of lattice distortion and crystal-field calculation of Cm3+ energy levels have been conducted to provide a quantitative interpretation of the experimental results. This method should be applicable to 4f- and 3d-ions in crystalline materials with lattice distortion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480587
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  • 2
    Electronic Resource
    Electronic Resource
    X-ray excited optical luminescence (XEOL) detection of x-ray absorption fine structure (XAFS) (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 6745-6752 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The x-ray excited optical luminescence (XEOL) from a variety of rare-earth ions was used as a detection mode for the collection of L-edge x-ray absorption fine-structure (XAFS) data. In order to understand the source of the observed optical signal, advantage is taken of the known luminescent response of f ions in a variety of transparent host materials. Whereas some samples exhibit an optical response that is indistinguishable from the transmission XAFS data, other samples show marked differences between the data obtained with the two different detection schemes. The unexpected optical luminescence of a Gd2O3 sample is traced to a Eu impurity. An optical spectrum of 0.4% Tb in Gd2O2S, excited by x-ray photons at the Gd edge, is used to demonstrate that the optical signal may arise from an ion different from the absorbing ion. The implications of this energy transfer are discussed in terms of the suitability of XEOL as a detection scheme for XAFS spectroscopy. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477320
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  • 3
    Electronic Resource
    Electronic Resource
    Raman heterodyne detection of magnetic resonance in a phosphate glass : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6512-6514 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A Raman heterodyne detection of magnetic resonance has been performed for probing the local structure of a sodium phosphate glass doped with trivalent europium. High resolution rf modulation spectra between 0.5 and 10 MHz were observed without the laser field in resonance with electronic transitions of the glass. The intensity of the observed Raman heterodyne signal depends on the external static magnetic field and sample temperature as well as the intensity of the laser and rf fields. The ability of monitoring the rf resonance spectra with micrometer spatial resolution may offer a potentially important means to probe the variation of local structure in disordered solid state materials. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361928
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetic phase diagram of Nd(Fe,Mo)12 alloys : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6226-6228 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic phase diagram of the alloy series NdFe12−xMox (x=1.0∼2.5) is obtained. Below the Curie temperature, the ferromagnetic phase is divided into three regions: Uniaxial, canted 1, and canted 2. At a temperature of Tsr1 (below 200 K) a spin reorientation transition (SRT) was observed for all the samples, and at Tsr2 (above 200 K) another SRT was found for samples with Mo concentration 1.5〈x〈1.75. At room temperature the easy direction of magnetization (EDM) of NdFe12−xMox changes from the c axis to a canted structure with increasing Mo concentration, with a critical composition of x=1.56. At low temperatures (below 100 K) all NdFe12−xMox compounds exhibit a canted moment structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355406
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  • 5
    Electronic Resource
    Electronic Resource
    Critical phenomena in the two-dimensional XY magnet Fe(100) on W(100) : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4984-4986 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We experimentally investigated the magnetic phase transition of the in-plane magnetized double-layer Fe on W(100). This epitaxial system approximates the theoretical two-dimensional (2D) XY model to a large extent because of its pseudomorphic growth and structural stability. We measured the magnetization of W(100)/Fe in the vicinity of the Curie temperature TC using the diffraction of spin polarized electrons and the magnetization of W(100)/Fe/Ag in a wider temperature interval using conversion electron Mössbauer spectroscopy. The temperature dependence of the spontaneous magnetization follows a power law with an exponent β=0.22±0.03 in the temperature regime 0.3≤T/TC≤0.99. The susceptibility χ(T(approximately-greater-than)TC) can be fitted alternatively by a power law with an unusually large exponent γ≈5 or by an exponential law χ∝exp(b/(square root of)T−TC), as predicted for the 2D XY model, with b=1.6. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361923
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  • 6
    Electronic Resource
    Electronic Resource
    Studies of local structure of Cm3+ in borosilicate glass using laser and x-ray spectroscopic methods and computational modeling (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 1489-1496 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The local environment of Cm3+ in a borosilicate glass has been probed by a combination of laser spectroscopy, structural modeling, and extended x-ray absorption fine structure (EXAFS) spectroscopy. The Stark splitting for the Cm f–f state transitions is significantly larger than the inhomogeneous line broadening that results from the disordered environment. As a result, the Cm optical spectrum can be fit using an effective operator Hamiltonian to obtain a set of crystal-field parameters. The fitting procedure, which requires the use of a descent-in-symmetry approach, provides a set of parameters for a best fit within tetragonal symmetry. These parameters are then linked to the local environment of Cm through exchange-charge modeling (ECM) of crystal field interactions. Cm in our borosilicate glass is best modeled with six oxygen ions with approximately tetragonal symmetry, and at an average distance of 2.31 (3) Å. The results of crystal-field modeling are supported by EXAFS results. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480687
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  • 7
    Electronic Resource
    Electronic Resource
    Crystal-field splitting, magnetic interaction, and vibronic excitations of 244Cm3+ in YPO4 and LuPO4 (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 6800-6808 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic and lattice-dynamical properties of 244Cm3+ doped orthophosphate crystals of YPO4 and LuPO4 were studied using site-selective fluorescence line narrowing (FLN) techniques. Although radiation damage caused substantial inhomogeneous line broadening, FLN gave rise to sharp resonant and satellite lines. Samples were annealed at 500 °C to eliminate satellite lines due to Cm3+ ions at different lattice environments. The crystal–field splitting of the nominal 8S7/2 ground state and the 6D7/2 excited state was determined from an analysis of the excitation and fluorescence spectra using an exchange charge model of crystal field interaction within the scheme of intermediate coupling. The effective g factors of the four Kramers doublets of the J=7/2 ground state and the lowest doublet of the excited state were evaluated from a least-squares fit of the observed Zeeman splitting to an effective-operator Hamiltonian. The energies of phonon modes were estimated from the observed vibronic spectra of the 244Cm3+ ion in both hosts and compared with the results of previous optical and neutron measurements. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477326
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  • 8
    Electronic Resource
    Electronic Resource
    Interaction of methanol and water on MgO(100) studied by ultraviolet photoelectron and metastable impact electron spectroscopies (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 2558-2565 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The coadsorption of methanol (CH3OH) and water (D2O) on the MgO(100)/Mo(100) surface at 100 K has been studied by metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy [UPS (HeI)], and by thermal programmed desorption (TPD). Methanol wets the MgO surface and adsorbs nondissociatively within the first monolayer with the hydroxyl group oriented toward the substrate. In coadsorption experiments, methanol wets a water precovered MgO surface; however, adding water to a methanol precovered MgO surface does not yield a water-only surface. Essentially, a constant fraction of the preadsorbed methanol remains within the topmost surface layer during the buildup of the water multilayer. Temperature-dependent measurements show that the adsorption and desorption dynamics of both water and methanol are governed by intermolecular interactions rather than adsorbate–substrate interactions. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477962
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  • 9
    Electronic Resource
    Electronic Resource
    Analysis of the crystal-field spectra of the actinide tetrafluorides. II. AmF4, CmF4, Cm4+:CeF4, and Bk4+:CeF4 (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 8277-8289 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report a systematic analysis of the crystal-field spectra of four fluoride compounds containing tetravalent actinide ions. The first part of this work [J. Chem. Phys. 95, 7194 (1991)] provided interpretation of the absorption spectra of UF4, NpF4, and PuF4. To extend our analysis to heavier elements of the series, low-temperature absorption spectra of AmF4 and CmF4, and site selective laser-induced emission and excitation spectra of Cm4+:CeF4 and Bk4+:CeF4 were obtained. A model energy level calculation was found to be in good agreement with the experimental results. It is shown that the crystal-field interaction in combination with spin–orbital coupling results in significant J mixing in the excited states, but ground state wave functions are still relatively pure in J character for the tetravalent actinide ions Am4+, Cm4+, and Bk4+. Trends in the parameters of the effective operator Hamiltonian are compared with those of a Hartree–Fock free-ion model. Interpretation of the ground-state splitting of the nominal S-state ion Bk4+ in CeF4 and color center formation in AmF4 are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468093
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  • 10
    Electronic Resource
    Electronic Resource
    Performance of Beamline 4W1C for x-ray diffuse scattering station at Beijing Synchrotron Radiation Facility : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1694-1695 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Bent triangular Si crystals with an oblique-cut angle 12.16° are used on the beamline 4W1C at Beijing Synchrotron Radiation Facility, to select monochromatic x-rays and to focus the beam in the horizontal direction. The downstream Pt-coated reflective mirror is bent as a cylindroid focuses the beam vertically. Double-focused monochromatic x rays are available on the diffuse scattering station. Specifications of the beamline with the Si (220) monochromator were measured as follows: size of the focus spot—0.5 mm (horizontal)×0.3 mm (vertical), maximum x-ray density—1.6×109 photons/s mm2, and energy resolution of the monochromatic beam—4.4×10−4. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145886
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