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Full-Text Articles in Physics

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 ...


Magnetostructural Transition In Gd5sb0.5ge3.5, A. S. Chernyshov, Yaroslav Mudryk, Durga Paudyal, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso Nov 2009

Magnetostructural Transition In Gd5sb0.5ge3.5, A. S. Chernyshov, Yaroslav Mudryk, Durga Paudyal, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso

Ames Laboratory Publications

Magnetic and crystallographic properties of Gd5Sb0.5Ge3.5 were investigated using dc magnetization, ac magnetic susceptibility, and heat capacity of an oriented single crystal, combined with temperature and magnetic field dependent x-ray powder diffraction. The compound undergoes an unusual magnetostructural transition at 40 K and a nonmagnetic second-order transition around 63 K. The detailed crystallographic study of Gd5Sb0.5Ge3.5 shows that contrary to the R5(SixGe1−x)4 systems (R is a rare-earth metal), the structural transition occurs without shear displacements of the 2[R ...


Electrical Resistivity And Magnetoresistance Of Single-Crystal Tb5si2.2ge1.8, Min Zou, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Yaroslav Mudryk, Deborah L. Schlagel, Thomas A. Lograsso Nov 2009

Electrical Resistivity And Magnetoresistance Of Single-Crystal Tb5si2.2ge1.8, Min Zou, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Yaroslav Mudryk, Deborah L. Schlagel, Thomas A. Lograsso

Ames Laboratory Publications

A positive colossal magnetoresistance (CMR) of 160% has been observed in Tb5Si2.2Ge1.8 with the magnetic field applied parallel to the a axis. When the magnetic field is applied parallel to the b and c axes, the magnetoresistance (MR) is less than 8% and 5%, respectively. The CMR effect originates from intrinsic crystallographic phase coexistence. The anisotropy of the MR effect is due to a unique geometric arrangement of the interphase boundaries and large magnetocrystalline anisotropy of the compound.


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 ...


Lattice Dynamics In Magnetic Superelastic Ni-Mn-In Alloys: Neutron Scattering And Ultrasonic Experiments, Xavier Moya, David González-Alonso, Lluís Mañosa, Antoni Planes, V. O. Garlea, Thomas A. Lograsso, Deborah L. Schlagel, Jerel L. Zarestky, Seda Aksoy, Mehmed Acet Jun 2009

Lattice Dynamics In Magnetic Superelastic Ni-Mn-In Alloys: Neutron Scattering And Ultrasonic Experiments, Xavier Moya, David González-Alonso, Lluís Mañosa, Antoni Planes, V. O. Garlea, Thomas A. Lograsso, Deborah L. Schlagel, Jerel L. Zarestky, Seda Aksoy, Mehmed Acet

Ames Laboratory Publications

Neutron scattering and ultrasonic methods have been used to study the lattice dynamics of two single crystals of Ni-Mn-In Heusler alloys close to Ni50Mn34In16 magnetic superelastic composition. The paper reports on the experimental determination of the low-lying phonon-dispersion curves and the elastic constants for this alloy system. We found that the frequencies of the TA2 branch are relatively low and it exhibits a small dip anomaly at a wave number ξ0≈1/3, which softens with decreasing temperature. Associated with the softening of this phonon, we also observed the softening of the shear ...


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 ...


Aperiodic And Modulated Pb Thin Films On Fivefold Icosahedral Al-Cu-Fe And Al(111): Tailoring The Structure Of Pb, Th. Deniozou, J. Ledieu, V. Fournée, D. M. Wu, Thomas A. Lograsso, H. I. Li, R. D. Diehl Jun 2009

Aperiodic And Modulated Pb Thin Films On Fivefold Icosahedral Al-Cu-Fe And Al(111): Tailoring The Structure Of Pb, Th. Deniozou, J. Ledieu, V. Fournée, D. M. Wu, Thomas A. Lograsso, H. I. Li, R. D. Diehl

Ames Laboratory Publications

We report on the growth of Pb thin films deposited either on the Al-rich fivefold surface of the icosahedral Al-Cu-Fe quasicrystal or on the (111) surface of fcc Al. On the quasicrystalline substrate, the diffusion length of Pb adatoms is short due to heterogeneous nucleation that enforces a quasiperiodic structure in the monolayer. On the Al(111) substrate, the mobility of Pb adatoms is high and the interaction with the substrate is flatter, leading to the formation of a (√31×√31)R8.95° higher-order commensurate structure. This moiré structure propagates up to the highest coverages investigated.


Nucleation Of Pb Starfish Clusters On The Five-Fold Al-Pd-Mn Quasicrystal Surface, J. Ledieu, M. Krajčí, J. Hafner, L. Leung, L. H. Wearing, R. Mcgrath, Thomas A. Lograsso, D. Wu, V. Fournée Apr 2009

Nucleation Of Pb Starfish Clusters On The Five-Fold Al-Pd-Mn Quasicrystal Surface, J. Ledieu, M. Krajčí, J. Hafner, L. Leung, L. H. Wearing, R. Mcgrath, Thomas A. Lograsso, D. Wu, V. Fournée

Ames Laboratory Publications

The nucleation of Pb clusters on the five-fold Al-Pd-Mn quasicrystal surface has been investigated using scanning tunneling microscopy (STM) and ab initio calculations based on density-functional theory (DFT). In the submonolayer regime, Pb atoms are highly mobile and adsorb preferentially within equatorially truncated pseudo-Mackay clusters present at the surface. The decoration of these unique adsorption sites leads to the formation of five-fold islands dubbed “starfish” and eventually to a quasiperiodic Pb monolayer. From a comparison of measured and calculated STM images it is concluded that most starfish clusters on all terraces are composed of ten Pb adatoms. A model of ...


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 ...


Magnetoelastic Coupling In Fe100−Xgex Single Crystals With 4, G. Petculescu, J. B. Leblanc, M. Wun-Fogle, J. B. Restorff, William M. Yuhasz, Thomas A. Lograsso, A. E. Clark Mar 2009

Magnetoelastic Coupling In Fe100−Xgex Single Crystals With 4, G. Petculescu, J. B. Leblanc, M. Wun-Fogle, J. B. Restorff, William M. Yuhasz, Thomas A. Lograsso, A. E. Clark

Ames Laboratory Conference Papers, Posters, and Presentations

In this paper we examine the elastic (c′ and c44) and magnetostrictive (λ100 and λ111) behaviors of Fe100−xGex for 4<x<18, quantities used further to find the fundamental magnetoelastic coupling constants b1 and b2 at room temperature. The x dependence ofb1 and b2 for Fe100−xGex is contrasted to those of Fe100−xGax and Fe100−xAlx. While the rhombohedral shear elastic constant c44 is almost insensitive to the type and amount of solute, the tetragonal shear constant c′ shows a pronounced and rapid softening with increasing x for ...


High-Pressure Study Of The Magnetic Phase Transition In Mnsi, Alla E. Petrova, Vladimir N. Krasnorussky, Thomas A. Lograsso, Sergei M. Stishov Mar 2009

High-Pressure Study Of The Magnetic Phase Transition In Mnsi, Alla E. Petrova, Vladimir N. Krasnorussky, Thomas A. Lograsso, Sergei M. Stishov

Ames Laboratory Publications

Measurements of ac magnetic susceptibility and dc resistivity of a high-quality single-crystal MnSi were carried out at high pressure making use of helium as a pressure medium. The form of the ac magnetic susceptibility curves at the magnetic phase transition suddenly changes upon helium solidification. This implies strong sensitivity of magnetic properties of MnSi to nonhydrostatic stresses and suggests that the early claims on the existence of a tricritical point at the phase-transition line are probably a result of misinterpretation of the experimental data. At the same time resistivity behavior at the phase transition does not show such a significant ...


Influence Of Annealing And Phase Decomposition On The Magnetostructural Transitions In Ni50mn39sn11, William M. Yuhasz, Deborah L. Schlagel, Qingfeng Xing, Kevin W. Dennis, R. William Mccallum, Thomas A. Lograsso Feb 2009

Influence Of Annealing And Phase Decomposition On The Magnetostructural Transitions In Ni50mn39sn11, William M. Yuhasz, Deborah L. Schlagel, Qingfeng Xing, Kevin W. Dennis, R. William Mccallum, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

Magnetic and structural transitions in the Ni50Mn50−xSnx (x = 10–25) ferromagnetic shape memory alloys are currently of interest. As in Ni–Mn–Ga, these alloys feature high-temperature austenite and low-temperature martensite phases, where the magnetic state is strongly composition dependent. To study the role of chemical ordering in fine-tuning their magnetostructural properties, they were first annealed for 4 weeks/1223 K to achieve structural and compositional homogeneity, and were then further annealed for 1 week ( ∼ 150 K below the reported B2 to L21 transition) at 773 K to increase the degree ...


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 ...