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Full-Text Articles in Physics

Magnetic Excitations And Anomalous Spin-Wave Broadening In Multiferroic Fev2o4, Qiang Zhang, Mehmet Ramazanoglu, Songxue Chi, Yong Liu, Thomas A. Lograsso, David Vaknin Jun 2014

Magnetic Excitations And Anomalous Spin-Wave Broadening In Multiferroic Fev2o4, Qiang Zhang, Mehmet Ramazanoglu, Songxue Chi, Yong Liu, Thomas A. Lograsso, David Vaknin

Ames Laboratory Publications

We report on the different roles of two orbital-active Fe2+ at the A site and V3+ at the B site in the magnetic excitations and on the anomalous spin-wave broadening in FeV2O4. FeV2O4 exhibits three structural transitions and successive paramagnetic (PM)–collinear ferrimagnetic (CFI)–noncollinear ferrimagnetic (NCFI)/ferroelectric transitions. The high-temperature tetragonal/PM–orthorhombic/CFI transition is accompanied by the appearance of a large energy gap in the magnetic excitations due to strong spin-orbit-coupling-induced anisotropy at the Fe2+ site. While there is no measurable increase in the energy gap from the orbital ordering of V3+ at the orthorhombic/CFI–tetragonal ...


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.


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 ...


Hydrostatic And Uniaxial Pressure Dependence Of Superconducting Transition Temperature Of Kfe2as2 Single Crystals, Sergey L. Bud'ko, Yong Liu, Thomas A. Lograsso, Paul C. Canfield Dec 2012

Hydrostatic And Uniaxial Pressure Dependence Of Superconducting Transition Temperature Of Kfe2as2 Single Crystals, Sergey L. Bud'ko, Yong Liu, Thomas A. Lograsso, Paul C. Canfield

Ames Laboratory Publications

We present heat capacity, c-axis thermal expansion and pressure-dependent, low-field, temperature-dependent magnetization for pressures up to ∼12 kbar, data for KFe2As2 single crystals. Tc decreases under pressure with dTc/dP≈−0.10 K/kbar. The inferred uniaxial, c-axis, pressure derivative is positive, dTc/dpc≈0.11 K/kbar. The data are analyzed in comparison with those for overdoped Fe-based superconductors. Arguments are presented that superconductivity in KFe2As2 may be different from the other overdoped, Fe-based materials in the 122 family.


X-Ray Diffuse Scattering Measurements Of Chemical Short-Range Order And Lattice Strains In A Highly Magnetostrictive Fe0.813ga0.187 Alloy In An Applied Magnetic Field, Yingzhou Du, Mianliang Huang, Thomas A. Lograsso, Robert J. Mcqueeney Jun 2012

X-Ray Diffuse Scattering Measurements Of Chemical Short-Range Order And Lattice Strains In A Highly Magnetostrictive Fe0.813ga0.187 Alloy In An Applied Magnetic Field, Yingzhou Du, Mianliang Huang, Thomas A. Lograsso, Robert J. Mcqueeney

Ames Laboratory Publications

The rapid growth of the magnetostriction coefficient of ferromagnetic Fe1−xGax alloys that occurs at a composition range from 0


Spatially Resolved Distribution Function And The Medium-Range Order In Metallic Liquid And Glass, X. W. Fang, Cai-Zhuang Wang, S. G. Hao, Matthew J. Kramer, Yongxin Yao, Mikhail I. Mendelev, Z. J. Ding, Ralph E. Napolitano, Kai-Ming Ho Dec 2011

Spatially Resolved Distribution Function And The Medium-Range Order In Metallic Liquid And Glass, X. W. Fang, Cai-Zhuang Wang, S. G. Hao, Matthew J. Kramer, Yongxin Yao, Mikhail I. Mendelev, Z. J. Ding, Ralph E. Napolitano, Kai-Ming Ho

Materials Science and Engineering Publications

The structural description of disordered systems has been a longstanding challenge in physical science. We propose an atomic cluster alignment method to reveal the development of three-dimensional topological ordering in a metallic liquid as it undercools to form a glass. By analyzing molecular dynamic (MD) simulation trajectories of a Cu64.5Zr35.5 alloy, we show that medium-range order (MRO) develops in the liquid as it approaches the glass transition. Specifically, around Cu sites, we observe “Bergman triacontahedron” packing (icosahedron, dodecahedron and icosahedron) that extends out to the fourth shell, forming an interpenetrating backbone network in the glass. The discovery of ...


Effect Of Carbon Addition On The Single Crystalline Magnetostriction Of Fe-X (X = Al And Ga) Alloys, Mianliang Huang, Yingzhou Du, Robert J. Mcqueeney, Thomas A. Lograsso Mar 2010

Effect Of Carbon Addition On The Single Crystalline Magnetostriction Of Fe-X (X = Al And Ga) Alloys, Mianliang Huang, Yingzhou Du, Robert J. Mcqueeney, Thomas A. Lograsso

Ames Laboratory Publications

The effect of carbon addition on the magnetostriction of Fe–Ga and Fe–Al alloys was investigated and is summarized in this study. It was found that the addition of carbon generally increased the magnetostriction over binary alloys of Fe–Ga and Fe–Al systems. The formation of carbide in the Fe–Ga–C alloys with a composition near D03 phase region decreased the magnetostriction drastically. Fe–Al–C and Fe–Ga–C alloys responded differently to thermal treatments; the magnetostriction in the quenched Fe–Al–C alloys is equal to or slightly lower than that of the slow ...


Relation Between Ga Ordering And Magnetostriction Of Fe-Ga Alloys Studied By X-Ray Diffuse Scattering, Y. Du, Mianliang Huang, S. Chang, Deborah L. Schlagel, Thomas A. Lograsso, Robert J. Mcqueeney Feb 2010

Relation Between Ga Ordering And Magnetostriction Of Fe-Ga Alloys Studied By X-Ray Diffuse Scattering, Y. Du, Mianliang Huang, S. Chang, Deborah L. Schlagel, Thomas A. Lograsso, Robert J. Mcqueeney

Ames Laboratory Publications

Transmission synchrotron diffraction was employed to characterize the Ga ordering in magnetostrictive Fe100−xGax alloys with Ga concentrations from 0 to 20.3 at. %. The experiments focused on the development of atomic short-range ordering (SRO) by analysis of the diffuse scattering appearing at superlattice positions of the D03 ordered alloy structure. No SRO was found for Ga concentrations less than 4 at. %. Between 13 and 20.3 at. %, D03-type SRO clusters are observed whose size increases with Ga concentration for both slow-cooled and quenched samples. Thermal quenching of the samples suppresses the cluster sizes ...


Flux Growth At Ambient Pressure Of Millimeter-Sized Single Crystals Of Lafeaso, Lafeaso1−Xfx, And Lafe1−Xcoxaso, J.-Q. Yan, Shibabrata Nandi, Jerel L. Zarestky, W. Tian, Andreas Kreyssig, Brandt A. Jensen, A. Kracher, Kevin W. Dennis, Robert J. Mcqueeney, Alan I. Goldman, R. William Mccallum, Thomas A. Lograsso Dec 2009

Flux Growth At Ambient Pressure Of Millimeter-Sized Single Crystals Of Lafeaso, Lafeaso1−Xfx, And Lafe1−Xcoxaso, J.-Q. Yan, Shibabrata Nandi, Jerel L. Zarestky, W. Tian, Andreas Kreyssig, Brandt A. Jensen, A. Kracher, Kevin W. Dennis, Robert J. Mcqueeney, Alan I. Goldman, R. William Mccallum, Thomas A. Lograsso

Ames Laboratory Publications

Millimeter-sized single crystals of LaFeAsO, LaFeAsO1−xFx, and LaFe1−xCoxAsO were grown in NaAs flux at ambient pressure. The detailed growth procedure and crystal characterizations are reported. The as-grown crystals have typical dimensions of3×4×0.05–0.3 mm3 with the crystallographic c-axis perpendicular to the plane of the platelike single crystals. Various characterizations confirmed the high quality of our LaFeAsO crystals. Co and F were introduced into the lattice leading to superconductingLaFe1−xCoxAsO and LaFeAsO1−xFx single crystals, respectively. This growth protocol ...


Single-Crystal Neutron Diffraction Study Of Short-Range Magnetic Correlations In Tb5ge4, W. Tian, Andreas Kreyssig, Jerel L. Zarestky, L. Tan, Shibabrata Nandi, Alan I. Goldman, Thomas A. Lograsso, Deborah L. Schlagel, Karl A. Gschneidner Jr., Vitalij K. Pecharsky, Robert J. Mcqueeney Oct 2009

Single-Crystal Neutron Diffraction Study Of Short-Range Magnetic Correlations In Tb5ge4, W. Tian, Andreas Kreyssig, Jerel L. Zarestky, L. Tan, Shibabrata Nandi, Alan I. Goldman, Thomas A. Lograsso, Deborah L. Schlagel, Karl A. Gschneidner Jr., Vitalij K. Pecharsky, Robert J. Mcqueeney

Ames Laboratory Publications

We present a single-crystal neutron diffraction study of the magnetic short-range correlations in Tb5Ge4 which orders antiferromagnetically below the Neel temperature TN≈92 K. Strong diffuse scattering arising from magnetic short-range correlations was observed in wide temperature ranges both below and above TN. The antiferromagnetic ordering in Tb5Ge4 is described to consist of strongly coupled ferromagnetic block layers in the ac plane that stack along the b axis with weak antiferromagnetic interlayer coupling. Diffuse scattering was observed along both a∗ and b∗ directions indicating three-dimensional short-range correlations. Moreover, the q dependence of ...


In Situ High Energy X-Ray Synchrotron Diffraction Study Of The Synthesis And Stoichiometry Of Lafeaso And Lafeaso1−Xfy, R. William Mccallum, J.-Q. Yan, Gustav E. Rustan, E. D. Mun, Yogesh Singh, S. Das, R. Nath, Sergey L. Bud'ko, Kevin W. Dennis, David C. Johnston, Paul C. Canfield, Matthew J. Kramer, Andreas Kreyssig, Thomas A. Lograsso, Alan I. Goldman Jun 2009

In Situ High Energy X-Ray Synchrotron Diffraction Study Of The Synthesis And Stoichiometry Of Lafeaso And Lafeaso1−Xfy, R. William Mccallum, J.-Q. Yan, Gustav E. Rustan, E. D. Mun, Yogesh Singh, S. Das, R. Nath, Sergey L. Bud'ko, Kevin W. Dennis, David C. Johnston, Paul C. Canfield, Matthew J. Kramer, Andreas Kreyssig, Thomas A. Lograsso, Alan I. Goldman

Ames Laboratory Publications

The reaction path for the synthesis of LaFeAsO and LaFeAsO1−xFy by solid state reaction was studied by in situ high temperature x-ray diffraction technique and differential thermal analysis in the temperature interval 100 °C ⩽ T ⩽ 1150 °C. Starting with LaAs, Fe2O3, Fe, and LaF3 as precursors, the results show that the synthesis is characterized by three temperature intervals: (1) Below 500 °C the sequential reduction of Fe2O3 and Fe3O4takes place through the oxidization of LaAs. Below 400 °C, Fe2O3 is reduced to ...


Single-Crystal Growth, Crystallography, Magnetic Susceptibility, Heat Capacity, And Thermal Expansion Of The Antiferromagnetic S=1 Chain Compound Cav2o4, A. Niazi, Sergey L. Bud'ko, Deborah L. Schlagel, J.-Q. Yan, Thomas A. Lograsso, Andreas Kreyssig, S. Das, Shibabrata Nandi, Alan I. Goldman, A. Honecker, R. William Mccallum, M. Reehuis, O. Pieper, B. Lake, David C. Johnston Mar 2009

Single-Crystal Growth, Crystallography, Magnetic Susceptibility, Heat Capacity, And Thermal Expansion Of The Antiferromagnetic S=1 Chain Compound Cav2o4, A. Niazi, Sergey L. Bud'ko, Deborah L. Schlagel, J.-Q. Yan, Thomas A. Lograsso, Andreas Kreyssig, S. Das, Shibabrata Nandi, Alan I. Goldman, A. Honecker, R. William Mccallum, M. Reehuis, O. Pieper, B. Lake, David C. Johnston

Ames Laboratory Publications

The compound CaV2O4 contains V+3 cations with spin S=1 and has an orthorhombic structure at room temperature containing zigzag chains of V atoms running along the c axis. We have grown single crystals of CaV2O4 and report crystallography, static magnetization, magnetic susceptibility χ, ac magnetic susceptibility, heat capacity Cp, and thermal expansion measurements in the temperature T range of 1.8–350 K on the single crystals and on polycrystalline samples. An orthorhombic-to-monoclinic structural distortion and a long-range antiferromagnetic (AF) transition were found at sample-dependent temperatures TS≈108–145 K ...


Low Temperature Heat Capacity Of Fe1−Xgax Alloys With Large Magnetostriction, J. M. Hill, Robert J. Mcqueeney, Ruqian Wu, Kevin W. Dennis, R. William Mccallum, Mianliang Huang, Thomas A. Lograsso Jan 2009

Low Temperature Heat Capacity Of Fe1−Xgax Alloys With Large Magnetostriction, J. M. Hill, Robert J. Mcqueeney, Ruqian Wu, Kevin W. Dennis, R. William Mccallum, Mianliang Huang, Thomas A. Lograsso

Ames Laboratory Publications

The low temperature heat capacity Cp of Fe1−xGax alloys with large magnetostriction has been investigated. The data were analyzed in the standard way using electron (γT) and phonon (βT3) contributions. The Debye temperature ΘD decreases approximately linearly with increasing Ga concentration, consistent with previous resonant ultrasound measurements and measured phonon dispersion curves. Calculations of ΘD from lattice dynamical models and from measured elastic constants C11,C12, and C44 are in agreement with the measured data. The linear coefficient of electronic specific heat γ remains relatively constant as the Ga concentration ...


Magnetic Structure Of Dy3+ In Hexagonal Multiferroic Dymno3, Shibabrata Nandi, Andreas Kreyssig, J.-Q. Yan, Matthew D. Vannette, J. C. Lang, L. Tan, J. W. Kim, Ruslan Prozorov, Thomas A. Lograsso, Robert J. Mcqueeney, Alan I. Goldman Aug 2008

Magnetic Structure Of Dy3+ In Hexagonal Multiferroic Dymno3, Shibabrata Nandi, Andreas Kreyssig, J.-Q. Yan, Matthew D. Vannette, J. C. Lang, L. Tan, J. W. Kim, Ruslan Prozorov, Thomas A. Lograsso, Robert J. Mcqueeney, Alan I. Goldman

Ames Laboratory Publications

Element specific x-ray resonant magnetic scattering (XRMS) investigations were undertaken to determine the magnetic structure of the multiferroic compound, hexagonal DyMnO3. In the temperature range from 68 K down to 8 K the Dy3+ moments are aligned and antiferromagnetically correlated in the c direction according to the magnetic representation Γ3. The temperature dependence of the observed intensity can be modeled assuming the splitting of ground-state doublet crystal-field levels of Dy3+ by the exchange field of Mn3+. XRMS together with magnetization measurements indicate that the magnetic representation is Γ2 below 8 K.


Structural Transition And Anisotropic Properties Of Single-Crystalline Srfe2as2, J.-Q. Yan, Andreas Kreyssig, Shibabrata Nandi, N. Ni, Sergey L. Bud'ko, Robert J. Mcqueeney, R. William Mccallum, Thomas A. Lograsso, Alan I. Goldman, Paul C. Canfield Jul 2008

Structural Transition And Anisotropic Properties Of Single-Crystalline Srfe2as2, J.-Q. Yan, Andreas Kreyssig, Shibabrata Nandi, N. Ni, Sergey L. Bud'ko, Robert J. Mcqueeney, R. William Mccallum, Thomas A. Lograsso, Alan I. Goldman, Paul C. Canfield

Ames Laboratory Publications

Platelike single crystals of SrFe2As2 as large as 3×3×0.5 mm3 have been grown out of Sn flux. The SrFe2As2 single crystals show a structural phase transition from a high-temperature tetragonal phase to a low-temperature orthorhombic phase at To=198 K, and do not show any sign of superconductivity down to 1.8 K. The structural transition is accompanied by an anomaly in the electrical resistivity, Hall resistivity, specific heat, and the anisotropic magnetic susceptibility. In an intermediate temperature range from 198 to 160 K, single-crystal x-ray diffraction suggests a coexistence ...


Spin-Flop Transition In Gd5ge4 Observed By X-Ray Resonant Magnetic Scattering And First-Principles Calculations Of Magnetic Anisotropy, L. Tan, Andreas Kreyssig, Shibabrata Nandi, S. Jia, Yongbin Lee, J. C. Lang, Z. Islam, Thomas A. Lograsso, Deborah L. Schlagel, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Paul C. Canfield, Bruce N. Harmon, Robert J. Mcqueeney, Alan I. Goldman Feb 2008

Spin-Flop Transition In Gd5ge4 Observed By X-Ray Resonant Magnetic Scattering And First-Principles Calculations Of Magnetic Anisotropy, L. Tan, Andreas Kreyssig, Shibabrata Nandi, S. Jia, Yongbin Lee, J. C. Lang, Z. Islam, Thomas A. Lograsso, Deborah L. Schlagel, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Paul C. Canfield, Bruce N. Harmon, Robert J. Mcqueeney, Alan I. Goldman

Ames Laboratory Publications

X-ray resonant magnetic scattering was employed to study a fully reversible spin-flop transition in orthorhombic Gd5Ge4 and to elucidate details of the magnetic structure in the spin-flop phase. The orientation of the moments at the three Gd sites flop 90° from the c axis to the a axis when a magnetic field, Hsf=9 kOe, is applied along the c axis at T=9 K. The magnetic space group changes from Pnm′a to Pn′m′a′ for all three Gd sublattices. The magnetic anisotropy energy determined from experimental measurements is in good agreement with the ...


17o And 51v Nmr For The Zigzag Spin-1 Chain Compound Cav2o4, X. Zong, B. J. Suh, A. Niazi, J.-Q. Yan, Deborah L. Schlagel, Thomas A. Lograsso, David C. Johnston Jan 2008

17o And 51v Nmr For The Zigzag Spin-1 Chain Compound Cav2o4, X. Zong, B. J. Suh, A. Niazi, J.-Q. Yan, Deborah L. Schlagel, Thomas A. Lograsso, David C. Johnston

Ames Laboratory Publications

51V NMR studies on CaV2O4 single crystals and 17O NMR studies on 17O-enriched powder samples are reported. The temperature dependences of the 17O NMR linewidth and nuclear spin-lattice relaxation rate give strong evidence for a long-range antiferromagnetic transition at TN=78 K in the powder. Magnetic susceptibility measurements show that TN=69 K in the crystals. A zero-field 51V NMR signal was observed at low temperatures (f≈237 MHz at 4.2 K) in the crystals. The field-swept spectra with the field in different directions suggest the presence of two antiferromagnetic substructures. Each substructure is ...


Magnetism Of (Dy0.5er0.5)Al2 Single Crystal In Ac And Dc Magnetic Fields, Evgenii M. Levin, Karl A. Gschneidner Jr., Thomas A. Lograsso, Deborah L. Schlagel Aug 2006

Magnetism Of (Dy0.5er0.5)Al2 Single Crystal In Ac And Dc Magnetic Fields, Evgenii M. Levin, Karl A. Gschneidner Jr., Thomas A. Lograsso, Deborah L. Schlagel

Ames Laboratory Publications

The temperature (4.2–90 K), ac magnetic field (1.25–50 Oe), frequency (5–125 Hz), and bias dc magnetic field (0–10 kOe) dependencies of the real and imaginary components of the ac magnetic susceptibility, and the temperature (4.2–250 K) and dc magnetic field(0.1–50 kOe) dependencies of the dc magnetic susceptibility and magnetization of a(Dy0.5Er0.5)Al2 single crystal have been studied. Isothermal magnetization measurement in a dc magnetic field indicates that (Dy0.5Er0.5)Al2 orders ferromagnetically at 37 K. The ac ...


Spectroscopic Ellipsometry Study Of Optical Anisotropy In Gd5si2ge2 And Comparison With Reflectance Difference Spectra, Joong Mok Park, David W. Lynch, S. J. Lee, Deborah L. Schlagel, Thomas A. Lograsso, A. O. Tsokol, J. E. Snyder, David C. Jiles Jan 2006

Spectroscopic Ellipsometry Study Of Optical Anisotropy In Gd5si2ge2 And Comparison With Reflectance Difference Spectra, Joong Mok Park, David W. Lynch, S. J. Lee, Deborah L. Schlagel, Thomas A. Lograsso, A. O. Tsokol, J. E. Snyder, David C. Jiles

Ames Laboratory Publications

The complex dielectric functions of single crystals of Gd5Si2Ge2 were obtained using spectroscopic ellipsometry (SE) in the photon energy range of 1.5–5.0 eV at room temperature. Reflectance difference (RD) spectra for the a‐b and b‐c planes of single crystals of Gd5Si2Ge2 were derived from these dielectric functions and compared to those obtained from reflectance difference spectroscopy (RDS) at near-normal incidence. The two experimental RD spectra from SE and RDS agreed well. The in-plane optical anisotropy of the sample is mainly due to intrinsic bulk properties ...


Small Sealed Ta Crucible For Thermal Analysis Of Volatile Metallic Samples, Y. Janssen, M. Angst, Kevin W. Dennis, Paul C. Canfield, R. William Mccallum Jan 2006

Small Sealed Ta Crucible For Thermal Analysis Of Volatile Metallic Samples, Y. Janssen, M. Angst, Kevin W. Dennis, Paul C. Canfield, R. William Mccallum

Ames Laboratory Publications

Differential thermal analysis on metallic alloys containing volatile elements can be highly problematic. Here we show how measurements can be performed in commercial, small-sample equipment without modification. This is achieved by using a sealed Ta crucible, easily fabricated from Ta tubing and sealed in a standard arc furnace. The crucible performance is demonstrated by measurements on a mixture of Mg and MgB2, after heating up to 1470°C. We also show data, measured on an alloy with composition Gd40Mg60, that clearly show both the liquidus and a peritectic and are consistent with published phase-diagram data.


Neutron Diffraction Studies Of The Magnetoelastic Compounds Tb5sixge4−X (X=2.2 And 2.5), V. O. Garlea, Jerel L. Zarestky, C. Y. Jones, L.-L. Lin, Deborah L. Schlagel, Thomas A. Lograsso, A. O. Tsokol, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., C. Stassis Sep 2005

Neutron Diffraction Studies Of The Magnetoelastic Compounds Tb5sixge4−X (X=2.2 And 2.5), V. O. Garlea, Jerel L. Zarestky, C. Y. Jones, L.-L. Lin, Deborah L. Schlagel, Thomas A. Lograsso, A. O. Tsokol, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., C. Stassis

Ames Laboratory Publications

We report the results of a neutron diffraction study, carried out on both single crystalline and polycrystalline samples of Tb5Si2.2Ge1.8 and polycrystalline Tb5Si2.5Ge1.5. On cooling, at approximately 120 K, the Tb5Si2.2Ge1.8 system undergoes a magnetoelastic transition from a high-temperature monoclinic-paramagnetic to a low-temperature orthorhombic-ferromagnetic structure. Between 120 K and 75 K, the magnetic structure has a net ferromagnetic component along the a axis direction. The moments are slightly canted with respect to the a axis, while the components along ...


Magnetic Structure Of Gd5ge4, L. Tan, Andreas Kreyssig, J. W. Kim, Alan I. Goldman, Robert J. Mcqueeney, D. Wermeille, B. Sieve, Thomas A. Lograsso, Deborah L. Schlagel, Sergey L. Bud'ko, Vitalij K. Pecharsky, Karl A. Gschneidner Jr. Jun 2005

Magnetic Structure Of Gd5ge4, L. Tan, Andreas Kreyssig, J. W. Kim, Alan I. Goldman, Robert J. Mcqueeney, D. Wermeille, B. Sieve, Thomas A. Lograsso, Deborah L. Schlagel, Sergey L. Bud'ko, Vitalij K. Pecharsky, Karl A. Gschneidner Jr.

Ames Laboratory Publications

Gd5Ge4 crystallizes in the orthorhombic space group Pnma, and orders antiferromagnetically below the Néel temperatureTN∼127 K. We have employed x-ray resonant magnetic scattering to elucidate the details of the magnetic structure. The magnetic unit cell is the same as the chemical unit cell. From azimuth scans and the Q dependence of the magnetic scattering, all three Gd sites in the structure were determined to be in the same magnetic space group Pnm′a. The magnetic moments are primarily aligned along the c axis and the c components of the magnetic moments at the three different ...


Elastic Constants Of Ni-Mn-Ga Magnetic Shape Memory Alloys, Marcelo Stipcich, Lluís Mañosa, Antoni Planes, Michel Morin, Jerel L. Zarestky, Thomas A. Lograsso, C. Stassis Aug 2004

Elastic Constants Of Ni-Mn-Ga Magnetic Shape Memory Alloys, Marcelo Stipcich, Lluís Mañosa, Antoni Planes, Michel Morin, Jerel L. Zarestky, Thomas A. Lograsso, C. Stassis

Ames Laboratory Publications

We have measured the adiabatic second order elastic constants of two Ni-Mn-Ga magnetic shape memory crystals with different martensitic transition temperatures, using ultrasonic methods. The temperature dependence of the elastic constants has been followed across the ferromagnetic transition and down to the martensitic transition temperature. Within experimental errors no noticeable change in any of the elastic constants has been observed at the Curie point. The temperature dependence of the shear elastic constant C′ has been found to be very different for the two alloys. Such a different behavior is in agreement with recent theoretical predictions for systems undergoing multi-stage structural ...


Electrical Transport In Amorphous Semiconducting Almgb14 Films, Y. Tian, G. Li, Joseph Shinar, N. L. Wang, Bruce A. Cook, James W. Anderegg, Alan P. Constant, Alan Mark Russell, J. E. Snyder Aug 2004

Electrical Transport In Amorphous Semiconducting Almgb14 Films, Y. Tian, G. Li, Joseph Shinar, N. L. Wang, Bruce A. Cook, James W. Anderegg, Alan P. Constant, Alan Mark Russell, J. E. Snyder

Materials Science and Engineering Publications

The electrical transport properties of semiconducting AlMgB14films deposited at room temperature and 573K are reported in this letter. The as-deposited films are amorphous, and they exhibit high n-type electrical conductivity, which is believed to stem from the conduction electrons donated by Al, Mg, and/or Fe impurities in these films. The film deposited at 573K is less conductive than the room-temperature-deposited film. This is attributed to the nature of donor or trap states in the band gap related to the different deposition temperatures.


Reversible Spin-Flop And Irreversible Metamagneticlike Transitions Induced By A Magnetic Field In The Layered Gd5ge4 Antiferromagnet, Evgenii M. Levin, Karl A. Gschneidner Jr., Thomas A. Lograsso, Deborah L. Schlagel, Vitalij K. Pecharsky Apr 2004

Reversible Spin-Flop And Irreversible Metamagneticlike Transitions Induced By A Magnetic Field In The Layered Gd5ge4 Antiferromagnet, Evgenii M. Levin, Karl A. Gschneidner Jr., Thomas A. Lograsso, Deborah L. Schlagel, Vitalij K. Pecharsky

Ames Laboratory Publications

Temperature and magnetic field dependencies of the magnetization of single crystal Gd5Ge4 indicate antiferromagnetic coupling along the c direction below 130 K. Both a reversible spin-flop transition when a magnetic field of ∼8.4kOe is applied along the cdirection, and irreversible metamagneticlike transitions when a 20 kOe or greater magnetic field is applied at 4.3 K along any of the three crystallographic axes are observed. Although Gd3+ ions have negligible single ion anisotropy, the metamagnetic transitions and magnetization of Gd5Ge4 in the ferromagnetic state depend on the crystallographic direction reflecting the anisotropy of ...


Reflectance Anisotropy Of Gd5si2ge2 And Tb5si2.2ge1.8, S. J. Lee, Joong Mok Park, J. E. Snyder, David C. Jiles, Deborah L. Schlagel, Thomas A. Lograsso, A. O. Pecharsky, David W. Lynch Mar 2004

Reflectance Anisotropy Of Gd5si2ge2 And Tb5si2.2ge1.8, S. J. Lee, Joong Mok Park, J. E. Snyder, David C. Jiles, Deborah L. Schlagel, Thomas A. Lograsso, A. O. Pecharsky, David W. Lynch

Ames Laboratory Publications

Reflectance difference (RD) spectra for the ab plane of the single crystals of Gd5Si2Ge2and bc planes of Gd5Si2Ge2 and Tb5Si2.2Ge1.8 were obtained in the photon energy range of 1.5–5.5 eV. Several peaks were observed for these crystals in the measured spectrum range. Similar features were observed in the RD spectra for the bc planes ofGd5Si2Ge2 and Tb5Si2.2Ge1.8, while different features were observed for the ...