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144 results on '"Toellner, T. S."'

24. Dynamics of iron atoms across the pressure-induced Invar transition in Pd_3Fe

Author

Winterrose, M. L., Mauger, L., Halevy, I., Yue, A. F., Lucas, M. S., Muñoz, J. A., Tan, Hongjin, Xiao, Y., Chow, P., Sturhahn, W., Toellner, T. S., Alp, E. E., and Fultz, B.

Abstract

The ^(57)Fe phonon partial density of states (PDOS) in L1_2-ordered Pd_3Fe was studied at high pressures by nuclear resonant inelastic x-ray scattering (NRIXS) measurements and density functional theory (DFT) calculations. The NRIXS spectra showed that the stiffening of the ^(57)Fe PDOS with decreasing volume was slower from 12 to 24 GPa owing to the pressure-induced Invar transition in Pd_3Fe, with a change from a high-moment ferromagnetic (FM) state to a low-moment (LM) state observed by nuclear forward scattering. Force constants obtained from fitting to a Born–von Kármán model showed a relative softening of the first-nearest-neighbor (1NN) Fe-Pd longitudinal force constants at the magnetic transition. For the FM low-pressure state, the DFT calculations gave a PDOS and 1NN longitudinal force constants in good agreement with experiment, but discrepancies for the high-pressure LM state suggest the presence of short-range magnetic order.

Published
2011

26. In situ x-ray diffraction studies of YBa2Cu3Ox/LaAlO3 interfaces.

Author

Williams, S. M., Wang, X. K., Maglic, S., Toellner, T. S., Lin, C. T., Cavanagh, M. D., Duray, S. J., Lundquist, P. M., Chang, R. P. H., and Ketterson, J. B.

Subjects
INTERFACES (Physical sciences), OPTICAL diffraction, X-rays
Abstract

Presents in-situ x-ray diffraction studies of YBa[sub2]Cu[sub3]O[subx]/LaAIO[sub3] interfaces. Experiment conducted; Results; Discussion.

Published
1994
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27. Atom clusters and vibrational excitations in chemically-disordered Pt357Fe

Author

Fultz, B., Stephens, T. A., Alp, E. E., Hu, M. Y., Sutter, J. P., Toellner, T. S., and Sturhahn, W.

Subjects
Physics::Atomic and Molecular Clusters, Caltech Library Services
Abstract

Inelastic nuclear resonant scattering spectra of Fe-57 atoms were measured on crystalline alloys of Pt3Fe-57 that were chemically disordered, partially ordered, and L1(2) ordered. Phonon partial density of states curves for Fe-57 were obtained from these spectra. Upon disordering, about 10% of the spectral intensity underwent a distinct shift from 25 to 19 meV. This change in optical modes accounted for most of the change of the vibrational entropy of disordering contributed by Fe atoms, which was (+0.10 +/- 0.03) k(B) (Fe atom)(-1). Prospects for parametrizing the vibrational entropy with low-order cluster variables were assessed. To calculate the difference in vibrational entropy of the disordered and ordered alloys, the clusters must be large enough to account for the abundances of several of the atom configurations of the first-nearest-neighbor shell about the Fe-57 atoms.

Published
2000

28. Local Chemical Environments and the Phonon Partial Densities of States of 57Fe in 57Fe3Al

Author

Fultz, B., Stephens, T. A., Sturhahn, W., Toellner, T. S., and Alp, E. E.

Subjects
Condensed Matter::Materials Science, Caltech Library Services
Abstract

Inelastic nuclear resonant scattering spectra were measured on alloys of Fe3Al that were chemically disordered, partially ordered, and D03 ordered. The features in the phonon partial density of states of 57Fe were found to change systematically with chemical short-range order in the alloy. Changes in the phonon partial density of states were modeled successfully by assigning vibrational spectra to 57Fe atoms in different first-nearest-neighbor chemical environments.

Published
1998

29. Electron emission from $\mathrm{^{57}Fe}$ nuclei excited with synchrotron radiation

Author

Sturhahn, W., Quast, K. W., Toellner, T. S., Alp, E. E., Metge, J., and Gerdau, E.

Subjects
Physics::Instrumentation and Detectors, Astrophysics::High Energy Astrophysical Phenomena, ddc:530, Astrophysics::Galaxy Astrophysics
Abstract

Physical review / B 53(1), 171 - 175 (1996). doi:10.1103/PhysRevB.53.171, Time-dependent electron emission from iron foils excited by synchrotron radiation at the 14.4-keV nuclear resonance of 57Fe was observed. The measured time spectra are explained as the sum of three contributions, the emission of conversion electrons with and without creating or annihilating phonons during absorption and the emission of photoelectrons., Published by APS, Woodbury, NY

Published
1996

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