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Iowa State University

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Metallurgy

Physics and Astronomy

Ames Laboratory Conference Papers, Posters, and Presentations

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Full-Text Articles in Physics

Magnetism Dependent Phonon Anomaly In Lafeaso Observed Via Inelastic X-Ray Scattering, Steven E. Hahn, Gregory S. Tucker, J.-Q. Yan, A. H. Said, B. M. Leu, R. William Mccallum, E. E. Alp, Thomas A. Lograsso, Robert J. Mcqueeney, Bruce N. Harmon Apr 2013

Magnetism Dependent Phonon Anomaly In Lafeaso Observed Via Inelastic X-Ray Scattering, Steven E. Hahn, Gregory S. Tucker, J.-Q. Yan, A. H. Said, B. M. Leu, R. William Mccallum, E. E. Alp, Thomas A. Lograsso, Robert J. Mcqueeney, Bruce N. Harmon

Ames Laboratory Conference Papers, Posters, and Presentations

The phonon dispersion was measured at room temperature (above the Néel temperature TN) along (0,0,L) in the tetragonal phase of LaFeAsO using inelastic x-ray scattering. Magnetostructural effects are well documented in the AFe2As2-based (A = Ca, Sr, Ba, Eu) systems. Only recently have single crystals of LaFeAsO become available. The experimentally observed splitting between two A1g phonon modes at 22 and 26 meV is only reproduced in spin-polarized calculations. Magnetostructural effects similar to those observed in the AFe2As2 materials are confirmed to be present in LaFeAsO. This is discussed ...


The Influence Of Growth Rate On Porosity In Al-Pd-Mn Icosahedral Quasicrystals, Amy R. Ross, Ian R. Fisher, Paul C. Canfield, Thomas A. Lograsso Jan 2000

The Influence Of Growth Rate On Porosity In Al-Pd-Mn Icosahedral Quasicrystals, Amy R. Ross, Ian R. Fisher, Paul C. Canfield, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

Growth experiments have been carried out to characterize the occurrence and development of porosity in Bridgman and flux grown Al-Pd-Mn icosahedral quasicrystals. The porosity level has been observed to fluctuate between values of 0.0 and 3.75 percent along the length of Bridgman single crystals implying that the development of porosity is affected by the local growth conditions. Experiments were conducted to evaluate the influence of the rate of solidification on the occurrence of porosity. Alloys were solidified with different growth rates, 1mm/hr and >10 mm/hr, using the Bridgman configuration and at different cooling rates, ranging from ...