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Articles 1 - 11 of 11

Full-Text Articles in Physics

Magnetic Structures And Interplay Between Rare-Earth Ce And Fe Magnetism In Single-Crystal Cefeaso, Qiang Zhang, Wei Tan, Haifeng Li, Jong-Woo Kim, Jiaqiang Yan, R. William Mccallum, Thomas A. Lograsso, Jerel L. Zarestky, Sergey L. Bud’Ko, Robert J. Mcqueeney, David Vaknin Nov 2013

Magnetic Structures And Interplay Between Rare-Earth Ce And Fe Magnetism In Single-Crystal Cefeaso, Qiang Zhang, Wei Tan, Haifeng Li, Jong-Woo Kim, Jiaqiang Yan, R. William Mccallum, Thomas A. Lograsso, Jerel L. Zarestky, Sergey L. Bud’Ko, Robert J. Mcqueeney, David Vaknin

Ames Laboratory Publications

Neutron and synchrotron resonant x-ray magnetic scattering (RXMS) complemented by heat capacity and resistivity measurements reveal the evolution of the magnetic structures of Fe and Ce sublattices in a CeFeAsO single crystal. The RXMS of magnetic reflections at the Ce L-II edge shows a magnetic transition that is specific to the Ce antiferromagnetic long-range ordering at T-Ce approximate to 4 K with short-range Ce ordering above T-Ce, whereas neutron diffraction measurements of a few magnetic reflections indicate a transition at T* approximate to 12 K with an unusual order parameter. Detailed order-parameter measurements on several magnetic reflections by neutrons show ...


Quantitative Vibrational Dynamics Of The Metal Site In A Tin Porphyrin: An Ir, Nrvs, And Dft Study, Bogdan M. Leu, Marek Z. Zgierski, Christian Michael Bischoff, Ming Li, Michael Y. Hu, Jiyoung Zhao, Steve W. Martin, Esen Ercan Alp, W. Robert Scheidt Sep 2013

Quantitative Vibrational Dynamics Of The Metal Site In A Tin Porphyrin: An Ir, Nrvs, And Dft Study, Bogdan M. Leu, Marek Z. Zgierski, Christian Michael Bischoff, Ming Li, Michael Y. Hu, Jiyoung Zhao, Steve W. Martin, Esen Ercan Alp, W. Robert Scheidt

Materials Science and Engineering Publications

We used a newer, synchrotron-based, spectroscopic technique (nuclear resonance vibrational spectroscopy, NRVS) in combination with a more traditional one (infrared absorption, IR) to obtain a complete, quantitative picture of the metal center vibrational dynamics in a six-coordinated tin porphyrin. From the NRVS 119Sn site-selectivity and the sensitivity of the IR signal to 112Sn/119Sn isotope substitution, we identified the frequency of the antisymmetric stretching of the axial bonds (290 cm–1) and all the other vibrations involving Sn. Experimentally authenticated density functional theory (DFT) calculations aid the data interpretation by providing detailed normal mode descriptions for each observed vibration. These ...


Multi-Channel Polarized Thermal Emitter, Jae-Hwang Lee, Kai-Ming Ho, Kristen P. Constant Jul 2013

Multi-Channel Polarized Thermal Emitter, Jae-Hwang Lee, Kai-Ming Ho, Kristen P. Constant

Iowa State University Patents

A multi-channel polarized thermal emitter (PTE) is presented. The multi-channelPTE can emit polarized thermal radiation without using a polarizer at normal emergence. The multi-channel PTE consists of two layers of metallic gratings on a monolithic and homogeneous metallic plate. It can be fabricated by a low-cost soft lithography technique called two-polymer microtransfer molding. The spectral positions of the mid-infrared (MIR) radiation peaks can be tuned by changing the periodicity of the gratings and the spectral separation between peaks are tuned by changing the mutual angle between the orientations of the two gratings.


Chip Segmentation In Machining: A Study Of Deformation Localization Characteristics In Ti6al4v, Abhijit Chandra, Pavan Karra, Adam Bragg, Jie Wang, Gap-Yong Kim Jun 2013

Chip Segmentation In Machining: A Study Of Deformation Localization Characteristics In Ti6al4v, Abhijit Chandra, Pavan Karra, Adam Bragg, Jie Wang, Gap-Yong Kim

Mechanical Engineering Conference Presentations, Papers, and Proceedings

Chip segmentation by deformation localization is an important process in a certain range of velocities and might be desirable in reducing cutting forces and by improving chips’ evacuation, whereas few studies of practical criteria to calculate shear band spacing are available in literature. This paper extends nonlinear dynamics model for chip segmentation by allowing time varying orientation of the shear plane that are pronounced in strain hardening materials. The model extends the non-linear dynamics approach with additional state variables to the Burns and Davies approach. The model is simulated numerically to predict the shear bands of the chip. The numerical ...


Texture And Grain Morphology Dependencies Of Saturation Magnetostriction In Rolled Polycrystalline Fe83ga17, R. A. Kellogg, A. B. Flatau, A. E. Clark, M. Wun-Fogle, Thomas A. Lograsso May 2013

Texture And Grain Morphology Dependencies Of Saturation Magnetostriction In Rolled Polycrystalline Fe83ga17, R. A. Kellogg, A. B. Flatau, A. E. Clark, M. Wun-Fogle, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

Textured polycrystalline Fe-Ga alloys exhibit magnetostrictive strains of 100 ppm or greater and may function as a mechanically robust actuator/sensing material. Current efforts seek to combine the 300+ ppm magnetostrictive strain performance of [100] oriented single crystals with the mechanical properties of polycrystalline forms. One approach to combining these properties is to control the crystallographic texture through deformation processing such as rolling. To determine the relationship between saturation magnetostriction, degree of texturing, and grain morphology we compare the results of three-dimensional finite element simulations with the analytical solution for a random polycrystal and the experimental responses of rolled polycrystalline ...


Two-Dimensional Magnetic Interactions In Lafeaso, Mehmet Ramazanoglu, J. Lamsal, Gregory S. Tucker, J.-Q. Yan, S. Calder, T. Guidi, T. Perring, R. William Mccallum, Thomas A. Lograsso, Andreas Kreyssig, Robert J. Mcqueeney Apr 2013

Two-Dimensional Magnetic Interactions In Lafeaso, Mehmet Ramazanoglu, J. Lamsal, Gregory S. Tucker, J.-Q. Yan, S. Calder, T. Guidi, T. Perring, R. William Mccallum, Thomas A. Lograsso, Andreas Kreyssig, Robert J. Mcqueeney

Ames Laboratory Publications

Inelastic neutron scattering measurements demonstrate that the magnetic interactions in antiferromagnetic LaFeAsO are two dimensional. Spin-wave velocities within the Fe layer and the magnitude of the spin gap are similar to the AFe2As2 based materials. However, the ratio of interlayer and intralayer exchange is found to be less than ∼10−4 in LaFeAsO, very similar to the cuprates, and ∼100 times smaller than that found in AFe2As2 compounds. The results suggest that the effective dimensionality of the magnetic system is highly variable in the parent compounds of the iron arsenides and weak three-dimensional interactions ...


Upper Critical Field Of High-Quality Single Crystals Of Kfe2as2, Yong Liu, Makariy A. Tanatar, Vladimir G. Kogan, Hyunsoo Kim, Thomas A. Lograsso, Ruslan Prozorov Apr 2013

Upper Critical Field Of High-Quality Single Crystals Of Kfe2as2, Yong Liu, Makariy A. Tanatar, Vladimir G. Kogan, Hyunsoo Kim, Thomas A. Lograsso, Ruslan Prozorov

Ames Laboratory Publications

Measurements of temperature-dependent in-plane resistivity ρ(T) were used to determine the upper critical field and its anisotropy in high-quality single crystals of the stoichiometric iron arsenide superconductor KFe2As2. The crystals were characterized by the residual resistivity ratio ρ(300 K)/ρ(0) up to 3000 and the resistive transition midpoint temperature Tc=3.8 K, significantly higher than in previous studies on the same material. We find increased Hc2(T) for both directions of the magnetic field, which scale with the increased Tc. This unusual linear Hc2(Tc) scaling is not ...


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 ...


Magnetism-Dependent Phonon Anomaly In Lafeaso Observed Via Inelastic X-Ray Scattering, S. 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 Mar 2013

Magnetism-Dependent Phonon Anomaly In Lafeaso Observed Via Inelastic X-Ray Scattering, S. 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 Publications

The phonon dispersion was measured at room temperature along (0,0,L) in the tetragonal phase of LaFeAsO using inelastic x-ray scattering. Spin-polarized first-principles calculations imposing various types of antiferromagnetic order are in better agreement with the experimental results than nonmagnetic calculations, although the measurements were made well above the magnetic ordering temperature, TN. Splitting observed 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 (A=Ca,Sr,Ba,Eu) materials are present in LaFeAsO. The inclusion of Fe ...


Native Defects In Tetradymite Bi2(Texse3−X) Topological Insulators, Linlin Wang, Mianliang Huang, Srinivasa Thimmaiah, Aftab Alam, Sergey L. Bud'ko, Adam Kaminski, Thomas A. Lograsso, Paul C. Canfield, Duane D. Johnson Mar 2013

Native Defects In Tetradymite Bi2(Texse3−X) Topological Insulators, Linlin Wang, Mianliang Huang, Srinivasa Thimmaiah, Aftab Alam, Sergey L. Bud'ko, Adam Kaminski, Thomas A. Lograsso, Paul C. Canfield, Duane D. Johnson

Ames Laboratory Publications

Formation energies of native defects in Bi2(TexSe3−x), with comparison to ideal Bi2Te2S, are calculated in density-functional theory to assess transport properties. Bi2Se3 is found to be n type for both Bi- and Se-rich growth conditions, while Bi2Te3 changes fromn to p type going from Te- to Bi-rich conditions, as observed. Bi2Te2Se and Bi2Te2S are generally n type, explaining observed heavily doped n-type behavior in most samples. A (0/−) transition level at 16 meV above valence-band maximum ...


Β-Mn-Type Co8+Xzn12–X As A Defect Cubic Laves Phase: Site Preferences, Magnetism, And Electronic Structure, Weiwei Xie, Srinvasa Timmaiah, Jagat Lamal, Jing Liu, Thomas W. Heitmann, Dante Quirinale, A. I. Goldman, Vitalij K. Pecharsky, Gordon J. Miller Jan 2013

Β-Mn-Type Co8+Xzn12–X As A Defect Cubic Laves Phase: Site Preferences, Magnetism, And Electronic Structure, Weiwei Xie, Srinvasa Timmaiah, Jagat Lamal, Jing Liu, Thomas W. Heitmann, Dante Quirinale, A. I. Goldman, Vitalij K. Pecharsky, Gordon J. Miller

Chemistry Publications

The results of crystallographic analysis, magnetic characterization, and theoretical assessment of β-Mn-type Co–Zn intermetallics prepared using high-temperature methods are presented. These β-Mn Co–Zn phases crystallize in the space group P4132 [Pearson symbol cP20; a = 6.3555(7)–6.3220(7)], and their stoichiometry may be expressed as Co8+xZn12–x [1.7(2) < x < 2.2(2)]. According to a combination of single-crystal X-ray diffraction, neutron powder diffraction, and scanning electron microscopy, atomic site occupancies establish clear preferences for Co atoms in the 8c sites and Zn atoms in the 12d sites, with all additional Co atoms replacing some Zn atoms, a result that can be rationalized by electronic structure calculations. Magnetic measurements and neutron powder diffraction of an equimolar Co:Zn sample confirm ferromagnetism in this phase with a Curie temperature of ∼420 K. Neutron powder diffraction and electronic structure calculations using the local spin density approximation indicate that the spontaneous magnetization of this phase arises exclusively from local moments at the Co atoms. Inspection of the atomic arrangements of Co8+xZn12–x reveals that the β-Mn aristotype may be derived from an ordered defect, cubic Laves phase (MgCu2-type) structure. Structural optimization procedures using the Vienna ab initio simulation package (VASP) and starting ...