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Full-Text Articles in Physics

Texture Development And Coercivity Enhancement In Cast Alnico 9 Magnets, Wenyong Zhang, Shah Valloppilly, Xingzhong Li, Lanping Yue, Ralph Skomski, Iver E. Anderson, Matthew J. Kramer, Wei Tang, Jeff Shield, David J. Sellmyer Dec 2017

Texture Development And Coercivity Enhancement In Cast Alnico 9 Magnets, Wenyong Zhang, Shah Valloppilly, Xingzhong Li, Lanping Yue, Ralph Skomski, Iver E. Anderson, Matthew J. Kramer, Wei Tang, Jeff Shield, David J. Sellmyer

Ames Laboratory Accepted Manuscripts

The effect of Y addition and magnetic field on texture and magnetic properties of arc-melted alnico 9 magnets has been investigated. Small additions of Y (1.5 wt.%) develop a (200) texture for the arc-melted alnico 9 magnet. Such a texture is hard to form in cast samples. To achieve this goal, we set up a high-field annealing system with a maximum operation temperature of 1250 °C. This system enabled annealing in a field of 45 kOe with subsequent draw annealing for the solutionized buttons; we have been able to substantially increase remanence ratio and coercivity, from 0.70 and ...


R14(Au, M)51 (R = Y, La−Nd, Sm−Tb, Ho, Er, Yb, Lu; M = Al, Ga, Ge, In,Sn, Sb, Bi): Stability Ranges And Site Preference In The Gd14ag51 Structure Type, Chris Celania, Volodymyr Smetana, Alessia Provino, Pietro Manfrinetti, Anja-Verena Mudring Dec 2017

R14(Au, M)51 (R = Y, La−Nd, Sm−Tb, Ho, Er, Yb, Lu; M = Al, Ga, Ge, In,Sn, Sb, Bi): Stability Ranges And Site Preference In The Gd14ag51 Structure Type, Chris Celania, Volodymyr Smetana, Alessia Provino, Pietro Manfrinetti, Anja-Verena Mudring

Ames Laboratory Accepted Manuscripts

Twenty new ternary representatives of the Gd14Ag51 structure type have been synthesized within the R-Au-M family (R = Y, La–Nd, Sm–Tb, Ho, Er, Yb, Lu; M = Al, Ga, Ge, In, Sn, Sb, Bi) using solid state synthesis techniques. The list of post transition metals (M) involved in the formation of this type of structure could be augmented by five new representatives. All compounds crystallize in the hexagonal space group P6/m (#175) with the unit cell ranges of a = 12.3136(2)–12.918(1) Å and c = 8.9967(3)–9.385(1) Å, and incorporate different ...


Diffusion Of Two-Dimensional Epitaxial Clusters On Metal (100) Surfaces: Facile Versus Nucleation-Mediated Behavior And Their Merging For Larger Sizes, King C. Lai, Da-Jiang Liu, James W. Evans Dec 2017

Diffusion Of Two-Dimensional Epitaxial Clusters On Metal (100) Surfaces: Facile Versus Nucleation-Mediated Behavior And Their Merging For Larger Sizes, King C. Lai, Da-Jiang Liu, James W. Evans

Ames Laboratory Accepted Manuscripts

For diffusion of two-dimensional homoepitaxial clusters of N atoms on metal (100) surfaces mediated by edge atom hopping, macroscale continuum theory suggests that the diffusion coefficient scales like DN∼N−β with β=3/2. However, we find quite different and diverse behavior in multiple size regimes. These include: (i) facile diffusion for small sizes N<9; (ii) slow nucleation-mediated diffusion with small β<1 for “perfect” sizes N=Np=L2 or L(L+1), for L=3,4, ... having unique ground-state shapes, for moderate sizes 9≤N≤O(102); the same also applies for N=Np+3, Np+4, ...(iii) facile diffusion but with large β>2 for N=Np+1 and Np+2 also for moderate sizes 9≤N≤O(102); (iv) merging of the above distinct branches and subsequent anomalous scaling with 1≲β<3/2, reflecting the quasifacetted structure of clusters, for larger N=O(102) to N=O(103); (v) classic scaling with β=3/2 for very large N=O(103) and above. The specified size ranges apply for typical model parameters. We focus on the moderate size regime where we show that diffusivity cycles quasiperiodically from the slowest branch for Np+3 (not Np) to the fastest branch for Np+1. Behavior is quantified by kinetic Monte Carlo simulation of an appropriate stochastic lattice-gas model. However, precise analysis must account for a strong enhancement of diffusivity for short time increments due to back correlation in the cluster motion. Further understanding of this enhancement, of anomalous size scaling behavior, and of the merging of various branches, is facilitated by combinatorial analysis of the number of the ground-state and low-lying excited state cluster configurations, and also of kink populations.


Optical Absorption Properties Of Ge2–44 And P-Doped Ge Nanoparticles, Wei Qin, Wen-Cai Lu, Li-Zhen Zhao, Kai-Ming Ho, Cai-Zhuang Wang Dec 2017

Optical Absorption Properties Of Ge2–44 And P-Doped Ge Nanoparticles, Wei Qin, Wen-Cai Lu, Li-Zhen Zhao, Kai-Ming Ho, Cai-Zhuang Wang

Ames Laboratory Accepted Manuscripts

The optical absorption properties of non-crystalline and crystalline Ge nanoparticles with the sizes from ∼2.5 to 15 Å have been studied at the B3LYP/6-31G level using time-dependent density functional theory. Hydrogen passivation and phosphorus doping on some selected Ge nanoparticles were also calculated. With the increase of cluster size, the optical absorption spectra of the non-crystalline Ge nanoparticles change from many peaks to a continuous broad band and at the same time exhibit a systematic red-shift. Doping phosphorus also causes the absorption spectra to shift toward the lower energy region for both non-crystalline and crystalline Ge nanoparticles. The ...


Communication: Diverse Nanoscale Cluster Dynamics: Diffusion Of 2d Epitaxial Clusters, King C. Lai, James W. Evans, Da-Jiang Liu Nov 2017

Communication: Diverse Nanoscale Cluster Dynamics: Diffusion Of 2d Epitaxial Clusters, King C. Lai, James W. Evans, Da-Jiang Liu

Ames Laboratory Accepted Manuscripts

The dynamics of nanoscale clusters can be distinct from macroscale behavior described by continuum formalisms. For diffusion of 2D clusters of N atoms in homoepitaxial systems mediated by edge atom hopping, macroscale theory predicts simple monotonic size scaling of the diffusion coefficient, DN ∼ N−β, with β = 3/2. However, modeling for nanoclusters on metal(100) surfaces reveals that slow nucleation-mediated diffusion displaying weak size scaling β < 1 occurs for “perfect” sizes Np = L2 and L(L+1) for integer L = 3,4,… (with unique square or near-square ground state shapes), and also for Np+3, Np+4,…. In contrast, fast facile nucleation-free diffusion displaying strong size scaling β ≈ 2.5 occurs for sizes Np+1 and Np+2. DN versus N oscillates strongly between the slowest branch (for Np+3) and the fastest branch (for Np+1). All branches merge for N = O(102), but macroscale behavior is only achieved for much larger N = O(103). This analysis reveals the unprecedented diversity of behavior on the nanoscale.


Thickness-Dependent Energetics For Pb Adatoms On Low-Index Pb Nanofilm Surfaces: First-Principles Calculations, Wei Li, Li Huang, Raj Ganesh S. Pala, Guang-Hong Lu, Feng Liu, James W. Evans, Yong Han Nov 2017

Thickness-Dependent Energetics For Pb Adatoms On Low-Index Pb Nanofilm Surfaces: First-Principles Calculations, Wei Li, Li Huang, Raj Ganesh S. Pala, Guang-Hong Lu, Feng Liu, James W. Evans, Yong Han

Physics and Astronomy Publications

Adsorption, interaction, and diffusion of adatoms on surfaces control growth and relaxation of epitaxial nanostructures and nanofilms. Previous reports of key diffusion barriers for Pb diffusion on low-index Pb surfaces are limited in scope and accuracy. Thus, we apply density functional theory (DFT) to calculate the adsorption and diffusion energetics for a Pb adatom on Pb(111), Pb(100), and Pb(110) nanofilms with different thicknesses. We find that these quantities exhibit damped oscillatory variation with increasing film thickness. For Pb(111) films, energetics along the minimum energy path for Pb adatom diffusion between adjacent fcc and hcp sites varies ...


Coexistence Of Type-Ii Dirac Point And Weak Topological Phase In Pt 3 Sn, Minsung Kim, Cai-Zhuang Wang, Kai-Ming Ho Nov 2017

Coexistence Of Type-Ii Dirac Point And Weak Topological Phase In Pt 3 Sn, Minsung Kim, Cai-Zhuang Wang, Kai-Ming Ho

Ames Laboratory Accepted Manuscripts

Intriguing topological phases may appear in both insulating and semimetallic states. Topological insulators exhibit topologically nontrivial band inversion, while topological Dirac/Weyl semimetals show “relativistic” linear band crossings. Here, we report an unusual topological state of Pt3Sn, where the two topological features appear simultaneously. Based on first-principles calculations, we show that Pt3Sn is a three-dimensional weak topological semimetal with topologically nontrivial band inversion between the valence and conduction bands, where the band structure also possesses type-II Dirac points at the boundary of two electron pockets. The formation of the Dirac points can be understood in terms of the representations of ...


Subsurface Bending And Reorientation Of Tilted Vortex Lattices In Bulk Isotropic Superconductors Due To Coulomb-Like Repulsion At The Surface, E. Herrera, I. Guillamon, J. A. Galvis, A. Correa, A. Fente, S. Vieira, H. Suderow, A. Yu. Martynovich, Vladimir G. Kogan Nov 2017

Subsurface Bending And Reorientation Of Tilted Vortex Lattices In Bulk Isotropic Superconductors Due To Coulomb-Like Repulsion At The Surface, E. Herrera, I. Guillamon, J. A. Galvis, A. Correa, A. Fente, S. Vieira, H. Suderow, A. Yu. Martynovich, Vladimir G. Kogan

Ames Laboratory Accepted Manuscripts

We study vortex lattices (VLs) in superconducting weak-pinning platelet-like single crystals of β−Bi2Pdin tilted magnetic fields with a scanning tunneling microscope. We show that vortices exit the sample perpendicular to the surface and are thus bent beneath the surface. The structure and orientation of the tilted VLs in the bulk are, for large tilt angles, strongly affected by Coulomb-type intervortex repulsion at the surface due to stray magnetic fields.


Doping Evolution Of The Anisotropic Upper Critical Fields In The Iron-Based Superconductor Ba1−Xkxfe2as2, Makariy A. Tanatar, Yong Liu, J. Jaroszynski,, J. S. Brooks, Thomas A. Lograsso, Ruslan Prozorov Nov 2017

Doping Evolution Of The Anisotropic Upper Critical Fields In The Iron-Based Superconductor Ba1−Xkxfe2as2, Makariy A. Tanatar, Yong Liu, J. Jaroszynski,, J. S. Brooks, Thomas A. Lograsso, Ruslan Prozorov

Ames Laboratory Accepted Manuscripts

In-plane resistivity measurements as a function of temperature and magnetic field up to 35 T with precise orientation within the crystallographic ac plane were used to study the upper critical field Hc2 of the hole-doped iron-based superconductor Ba1−xKxFe2As2. Compositions of the samples studied spanned from under- doped x=0.17 (Tc=12 K) and x=0.22 (Tc=20 K), both in the coexistence range of stripe magnetism and superconductivity, through optimal doping x=0.39 (Tc=38.4 K) and x=0.47 (Tc=37.2 K), to overdoped x=0.65 (Tc=22 K) and x=0 ...


Determining The Vortex Tilt Relative To A Superconductor Surface, Vladimir G. Kogan, J. R. Kirtley Nov 2017

Determining The Vortex Tilt Relative To A Superconductor Surface, Vladimir G. Kogan, J. R. Kirtley

Ames Laboratory Accepted Manuscripts

It is of interest to determine the exit angle of a vortex from a superconductor surface, since this affects the intervortex interactions and their consequences. Two ways to determine this angle are to image the vortex magnetic fields above the surface, or the vortex core shape at the surface. In this work we evaluate the field h(x,y,z) above a flat superconducting surface x,y and the currents J(x,y) at that surface for a straight vortex tilted relative to the normal to the surface, for both the isotropic and anisotropic cases. In principle, these results can ...


Reorientations, Relaxations, Metastabilities, And Multidomains Of Skyrmion Lattices, L. J. Bannenberg, F. Qian, R. M. Dalgliesh, N. Martin, G. Chaboussant, M. Schmidt, Deborah L. Schlagel, Thomas A. Lograsso, Diamond Light Source Ltd., C. Pappas Nov 2017

Reorientations, Relaxations, Metastabilities, And Multidomains Of Skyrmion Lattices, L. J. Bannenberg, F. Qian, R. M. Dalgliesh, N. Martin, G. Chaboussant, M. Schmidt, Deborah L. Schlagel, Thomas A. Lograsso, Diamond Light Source Ltd., C. Pappas

Ames Laboratory Accepted Manuscripts

Magnetic skyrmions are nanosized topologically protected spin textures with particlelike properties. They can form lattices perpendicular to the magnetic field, and the orientation of these skyrmion lattices with respect to the crystallographic lattice is governed by spin-orbit coupling. By performing small-angle neutron scattering measurements, we investigate the coupling between the crystallographic and skyrmion lattices in both Cu2OSeO3 and the archetype chiral magnet MnSi. The results reveal that the orientation of the skyrmion lattice is primarily determined by the magnetic field direction with respect to the crystallographic lattice. In addition, it is also influenced by the magnetic history of the sample ...


Capping Ligand Vortices As “Atomic Orbitals” In Nanocrystal Self-Assembly, Curt Waltmann, Nathan Horst, Alex Travesset Oct 2017

Capping Ligand Vortices As “Atomic Orbitals” In Nanocrystal Self-Assembly, Curt Waltmann, Nathan Horst, Alex Travesset

Ames Laboratory Accepted Manuscripts

We present a detailed analysis of the interaction between two nanocrystals capped with ligands consisting of hydrocarbon chains by united atom molecular dynamics simulations. We show that the bonding of two nanocrystals is characterized by ligand textures in the form of vortices. These results are generalized to nanocrystals of different types (differing core and ligand sizes) where the structure of the vortices depends on the softness asymmetry. We provide rigorous calculations for the binding free energy, show that these energies are independent of the chemical composition of the cores, and derive analytical formulas for the equilibrium separation. We discuss the ...


Superelasticity And Cryogenic Linear Shape Memory Effects Of Cafe2as2, John T. Sypek, Hang Yu, Keith J. Dusoe, Gil Drachuck, Hetal Patel, Amanda M. Giroux, Alan I. Goldman, Andreas Kreyssig, Paul C. Canfield, Serguei L. Bud’Ko, Christopher R. Weinberger, Seok-Woo Lee Oct 2017

Superelasticity And Cryogenic Linear Shape Memory Effects Of Cafe2as2, John T. Sypek, Hang Yu, Keith J. Dusoe, Gil Drachuck, Hetal Patel, Amanda M. Giroux, Alan I. Goldman, Andreas Kreyssig, Paul C. Canfield, Serguei L. Bud’Ko, Christopher R. Weinberger, Seok-Woo Lee

Ames Laboratory Accepted Manuscripts

Shape memory materials have the ability to recover their original shape after a significant amount of deformation when they are subjected to certain stimuli, for instance, heat or magnetic fields. However, their performance is often limited by the energetics and geometry of the martensitic-austenitic phase transformation. Here, we report a unique shape memory behavior in CaFe2As2, which exhibits superelasticity with over 13% recoverable strain, over 3 GPa yield strength, repeatable stress–strain response even at the micrometer scale, and cryogenic linear shape memory effects near 50 K. These properties are acheived through a reversible uni-axial phase transformation mechanism, the tetragonal ...


Extremely Large Magnetoresistance And Kohler's Rule In Pdsn4 : A Complete Study Of Thermodynamic, Transport, And Band-Structure Properties, Na Hyan Jo, Yun Wu, Lin-Lin Wang, Peter Orth, Savannah S. Downing, Soham Manni, Dixiang Mou, Duane D. Johnson, Adam Kaminski, Sergey L. Bud’Ko, Paul C. Canfield Oct 2017

Extremely Large Magnetoresistance And Kohler's Rule In Pdsn4 : A Complete Study Of Thermodynamic, Transport, And Band-Structure Properties, Na Hyan Jo, Yun Wu, Lin-Lin Wang, Peter Orth, Savannah S. Downing, Soham Manni, Dixiang Mou, Duane D. Johnson, Adam Kaminski, Sergey L. Bud’Ko, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

The recently discovered material PtSn4 is known to exhibit extremely large magnetoresistance (XMR) that also manifests Dirac arc nodes on the surface. PdSn4 is isostructural to PtSn4 with the same electron count. We report on the physical properties of high-quality single crystals of PdSn4 including specific heat, temperature- and magnetic-field-dependent resistivity and magnetization, and electronic band-structure properties obtained from angle-resolved photoemission spectroscopy (ARPES). We observe that PdSn4 has physical properties that are qualitatively similar to those of PtSn4, but find also pronounced differences. Importantly, the Dirac arc node surface state of PtSn4 is gapped out for PdSn4. By comparing these ...


Nucleation And Growth Kinetics For Intercalated Islands During Deposition On Layered Materials With Isolated Point-Like Surface Defects, Yong Han, Ann Lii-Rosales, Y. Zhou, C.-J. Wang, M. Kim, Michael C. Tringides, Cai-Zhuang Wang, Patricia A. Thiel, James W. Evans Oct 2017

Nucleation And Growth Kinetics For Intercalated Islands During Deposition On Layered Materials With Isolated Point-Like Surface Defects, Yong Han, Ann Lii-Rosales, Y. Zhou, C.-J. Wang, M. Kim, Michael C. Tringides, Cai-Zhuang Wang, Patricia A. Thiel, James W. Evans

Ames Laboratory Accepted Manuscripts

Theory and stochastic lattice-gas modeling is developed for the formation of intercalated metal islands in the gallery between the top layer and the underlying layer at the surface of layered materials. Our model for this process involves deposition of atoms, some fraction of which then enter the gallery through well-separated point-like defects in the top layer. Subsequently, these atoms diffuse within the subsurface gallery leading to nucleation and growth of intercalated islands nearby the defect point source. For the case of a single point defect, continuum diffusion equation analysis provides insight into the nucleation kinetics. However, complementary tailored lattice-gas modeling ...


Interfacial Self-Assembly Of Polyelectrolyte-Capped Gold Nanoparticles, Honghu Zhang, Srikanth Nayak, Wenjie Wang, Surya K Mallapragada, David Vaknin Oct 2017

Interfacial Self-Assembly Of Polyelectrolyte-Capped Gold Nanoparticles, Honghu Zhang, Srikanth Nayak, Wenjie Wang, Surya K Mallapragada, David Vaknin

Ames Laboratory Accepted Manuscripts

We report on pH- and salt-responsive assembly of nanoparticles capped with polyelectrolytes at vapor–liquid interfaces. Two types of alkylthiol-terminated poly(acrylic acid) (PAAs, varying in length) are synthesized and used to functionalize gold nanoparticles (AuNPs) to mimic similar assembly effects of single-stranded DNA-capped AuNPs using synthetic polyelectrolytes. Using surface-sensitive X-ray scattering techniques, including grazing incidence small-angle X-ray scattering (GISAXS) and X-ray reflectivity (XRR), we demonstrate that PAA-AuNPs spontaneously migrate to the vapor–liquid interfaces and form Gibbs monolayers by decreasing the pH of the suspension. The Gibbs monoalyers show chainlike structures of monoparticle thickness. The pH-induced self-assembly is attributed ...


Off-Axis Electron Holography Of Bacterial Cells And Magnetic Nanoparticles In Liquid, Tanya Prozorov, Trevor Alemeida, András Kovács, Rafal E. Dunin-Borkowski Oct 2017

Off-Axis Electron Holography Of Bacterial Cells And Magnetic Nanoparticles In Liquid, Tanya Prozorov, Trevor Alemeida, András Kovács, Rafal E. Dunin-Borkowski

Ames Laboratory Accepted Manuscripts

The mapping of electrostatic potentials and magnetic fields in liquids using electron holography has been considered to be unrealistic. Here, we show that hydrated cells of Magnetospirillum magneticum strain AMB-1 and assemblies of magnetic nanoparticles can be studied using off-axis electron holography in a fluid cell specimen holder within the transmission electron microscope. Considering that the holographic object and reference wave both pass through liquid, the recorded electron holograms show sufficient interference fringe contrast to permit reconstruction of the phase shift of the electron wave and mapping of the magnetic induction from bacterial magnetite nanocrystals. We assess the challenges of ...


Pressure Induced Half-Collapsed-Tetragonal Phase In Cakfe4as4, Udhara Kaluarachchi, Valentin Taufour, Aashish Sapkota, Vladislav Borisov, Tai Kong, W. R. Meier, Karunakar Kothapalli, Benjamin G. Ueland, Andreas Kreyssig, Roser Valenti, Robert J. Mcqueeney, Alan I. Goldman, Sergey L. Bud'ko, Paul C. Canfield Oct 2017

Pressure Induced Half-Collapsed-Tetragonal Phase In Cakfe4as4, Udhara Kaluarachchi, Valentin Taufour, Aashish Sapkota, Vladislav Borisov, Tai Kong, W. R. Meier, Karunakar Kothapalli, Benjamin G. Ueland, Andreas Kreyssig, Roser Valenti, Robert J. Mcqueeney, Alan I. Goldman, Sergey L. Bud'ko, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

We report the temperature-pressure phase diagram of CaKFe4As4 established using high-pressure electrical resistivity, magnetization, and high-energy x-ray diffraction measurements up to 6 GPa. With increasing pressure, both resistivity and magnetization data show that the bulk superconducting transition of CaKFe4As4 is suppressed and then disappears at p≳4 GPa. High-pressure x-ray data clearly indicate a phase transition to a collapsed tetragonal phase in CaKFe4As4 under pressure that coincides with the abrupt loss of bulk superconductivity near 4 GPa. The x-ray data, combined with resistivity data, indicate that the collapsed tetragonal transition line is essentially independent of pressure, occurring at 4.0 ...


A Benign Synthesis Of Alane By The Composition-Controlled Mechanochemical Reaction Of Sodium Hydride And Aluminum Chloride, Ihor Z. Hlova, Jennifer Goldston, Shalbh Gupta, Takeshi Kobayashi, Marek Pruski, Vitalij K. Pecharsky Oct 2017

A Benign Synthesis Of Alane By The Composition-Controlled Mechanochemical Reaction Of Sodium Hydride And Aluminum Chloride, Ihor Z. Hlova, Jennifer Goldston, Shalbh Gupta, Takeshi Kobayashi, Marek Pruski, Vitalij K. Pecharsky

Ames Laboratory Accepted Manuscripts

Solid-state mechanochemical synthesis of alane (AlH3) starting from sodium hydride (NaH) and aluminum chloride (AlCl3) has been achieved at room temperature. The transformation pathway of this solid-state reaction was controlled by a step-wise addition of AlCl3 to the initial reaction mixture that contained sodium hydride in excess of stoichiometric amount. As in the case of previously investigated LiH-AlCl3 system, complete selectivity was achieved whereby formation of unwanted elemental aluminum was fully suppressed, and AlH3 was obtained in quantitative yield. Reaction progress during each step was investigated by means of solid-state NMR and powder X-ray diffraction ...


Structural Hierarchy As A Key To Complex Phase Selection In Al-Sm, Zhuo Ye, Yang Sun, Manh Cuong Nguyen, Shihuai Zhou, Lin Zhou, Fanqiang Meng, Ryan T. Ott, E. Park, Matthew Besser, Matthew J. Kramer, Z. J. Ding, Mikhail I. Mendelev, Cai-Zhuang Wang, Ralph E. Napolitano, Kai-Ming Ho Oct 2017

Structural Hierarchy As A Key To Complex Phase Selection In Al-Sm, Zhuo Ye, Yang Sun, Manh Cuong Nguyen, Shihuai Zhou, Lin Zhou, Fanqiang Meng, Ryan T. Ott, E. Park, Matthew Besser, Matthew J. Kramer, Z. J. Ding, Mikhail I. Mendelev, Cai-Zhuang Wang, Ralph E. Napolitano, Kai-Ming Ho

Ames Laboratory Accepted Manuscripts

Investigating the unknown structure of the complex cubic phase, previously observed to crystallize from melt-spun amorphous Al–10 at.% Sm alloy, we determine the structure in full site-occupancy detail, highlighting several critical structural features that govern the far-from-equilibrium phase selection pathway. Using an efficient genetic algorithm combining molecular dynamics, density functional theory, and x-ray diffraction, the structure is clearly identified as body-centered cubic Im¯3m (No. 229) with ∼140 atoms per cubic unit cell and a lattice parameter of 1.4 nm. The complex structure is further refined to elucidate the detailed site occupancy, revealing full Sm occupancy on 6b ...


Tunable Dimensional Crossover And Magnetocrystalline Anisotropy In Fe 2 P -Based Alloys, I. A. Zhuravlev, Vladimir P. Antropov, A. Vishina, M. Van Schilfgaarde, K. D. Belashchenko Oct 2017

Tunable Dimensional Crossover And Magnetocrystalline Anisotropy In Fe 2 P -Based Alloys, I. A. Zhuravlev, Vladimir P. Antropov, A. Vishina, M. Van Schilfgaarde, K. D. Belashchenko

Ames Laboratory Accepted Manuscripts

Electronic structure calculations are used to examine the magnetic properties of Fe2P-based alloys and the mechanisms through which the Curie temperature and magnetocrystalline anisotropy can be optimized for specific applications. It is found that at elevated temperatures the magnetic interaction in pure Fe2P develops a pronounced two-dimensional character due to the suppression of the magnetization in one of the sublattices, but the interlayer coupling is very sensitive to band filling and structural distortions. This feature suggests a natural explanation for the observed sharp enhancement of the Curie temperature by alloying with multiple elements, such as Co, Ni, Si, and B ...


Near Infrared And Optical Beam Steering And Frequency Splitting In Air Holes-In-Silicon Inverse Photonic Crystals, Anna Tasolamprou, Thomas Koschny, Maria Kafesaki, Costas Soukoulis Sep 2017

Near Infrared And Optical Beam Steering And Frequency Splitting In Air Holes-In-Silicon Inverse Photonic Crystals, Anna Tasolamprou, Thomas Koschny, Maria Kafesaki, Costas Soukoulis

Ames Laboratory Accepted Manuscripts

We present the design of a dielectric inverse photonic crystal structure that couples line-defect waveguide propagating modes into highly directional beams of controllable directionality. The structure utilizes a triangular lattice made of air holes drilled in an infinitely thick Si slab, and it is designed for operation in the near-infrared and optical regime. The structure operation is based on the excitation and manipulation of dark dielectric surface states, in particular on the tailoring of the dark states’ coupling to outgoing radiation. This coupling is achieved with the use of properly designed external corrugations. The structure adapts and matches modes that ...


Relation Of Short-Range And Long-Range Lithium Ion Dynamics In Glass-Ceramics: Insights From Li-7 Nmr Field-Cycling And Field-Gradient Studies, Michael Haaks, Steve W. Martin, Michael Vogel Sep 2017

Relation Of Short-Range And Long-Range Lithium Ion Dynamics In Glass-Ceramics: Insights From Li-7 Nmr Field-Cycling And Field-Gradient Studies, Michael Haaks, Steve W. Martin, Michael Vogel

Materials Science and Engineering Publications

We use various Li-7 NMR methods to investigate lithium ion dynamics in 70Li(2)S-30P(2)S(5) glass and glass-ceramic obtained from this glass after heat treatment. We employ Li-7 spin-lattice relaxometry, including field-cycling measurements, and line-shape analysis to investigate short-range ion jumps as well as Li-7 field-gradient approaches to characterize long-range ion diffusion. The results show that ceramization substantially enhances the lithium ion mobility on all length scales. For the 70Li(2)S-30P(2)S(5) glass-ceramic, no evidence is found that bimodal dynamics result from different ion mobilities in glassy and crystalline regions of this sample. Rather ...


Polar Intermetallics Pr5co2ge3 And Pr7co2ge4 With Planar Hydrocarbon‐Like Metal Clusters, Qisheng Lin, Kaiser Aguirre, Scott M. Saunders, Timothy A. Hackett, Yong Liu, Valentin Taufour, Durga Paudyal, Sergey L. Bud’Ko, Paul C. Canfield, Gordon J. Miller Aug 2017

Polar Intermetallics Pr5co2ge3 And Pr7co2ge4 With Planar Hydrocarbon‐Like Metal Clusters, Qisheng Lin, Kaiser Aguirre, Scott M. Saunders, Timothy A. Hackett, Yong Liu, Valentin Taufour, Durga Paudyal, Sergey L. Bud’Ko, Paul C. Canfield, Gordon J. Miller

Chemistry Publications

Planar hydrocarbon‐like metal clusters may foster new insights linking organic molecules with conjugated π–π bonding interactions and inorganic structures in terms of their bonding characteristics. However, such clusters are uncommon in polar intermetallics. Herein, we report two polar intermetallic phases, Pr5Co2Ge3 and Pr7Co2Ge4, both of which feature such planar metal clusters, namely, ethylene‐like [Co2Ge4] clusters plus the concatenated forms and polyacene‐like [Co2Ge2]n ribbons in Pr5Co2Ge3, and 1,2,4,5‐tetramethylbenzene‐like [Co4Ge6] cluster in Pr7Co2Ge4. Just as in the related planar organic structures, these metal–metalloid species are dominated by covalent bonding interactions. Both ...


Magnetic Fluctuations, Precursor Phenomena, And Phase Transition In Mnsi Under A Magnetic Field, C. Pappas, L. J. Bannenberg, E. Lelièvre-Berna, F. Qian, C. D. Dewhurst, R. M. Dalgliesh, Deborah L. Schlagel, Thomas A. Lograsso, P. Falus Jul 2017

Magnetic Fluctuations, Precursor Phenomena, And Phase Transition In Mnsi Under A Magnetic Field, C. Pappas, L. J. Bannenberg, E. Lelièvre-Berna, F. Qian, C. D. Dewhurst, R. M. Dalgliesh, Deborah L. Schlagel, Thomas A. Lograsso, P. Falus

Ames Laboratory Publications

The reference chiral helimagnet MnSi is the first system where Skyrmion lattice correlations have been reported. At a zero magnetic field the transition at TC to the helimagnetic state is of first order. Above TC, in a region dominated by precursor phenomena, neutron scattering shows the buildup of strong chiral fluctuating correlations over the surface of a sphere with radius 2π/ℓ, where ℓ is the pitch of the helix. It has been suggested that these fluctuating correlations drive the helical transition to first order following a scenario proposed by Brazovskii for liquid crystals. We present a comprehensive neutron scattering ...


Chemical Disorder In Topological Insulators: A Route To Magnetism Tolerant Topological Surface States, M. Carmen Martínez-Velarte, Bernhard Kretz, María Moro-Lagares, Myriam H. Aguirre, Trevor A. Riedemann, Thomas A. Lograsso, Luis MorellóN, M. Ricardo Ibarra, AráN Garcia-Lekue, David Serrate Jul 2017

Chemical Disorder In Topological Insulators: A Route To Magnetism Tolerant Topological Surface States, M. Carmen Martínez-Velarte, Bernhard Kretz, María Moro-Lagares, Myriam H. Aguirre, Trevor A. Riedemann, Thomas A. Lograsso, Luis MorellóN, M. Ricardo Ibarra, AráN Garcia-Lekue, David Serrate

Materials Science and Engineering Publications

We show that the chemical inhomogeneity in ternary three-dimensional topological insulators preserves the topological spin texture of their surface states against a net surface magnetization. The spin texture is that of a Dirac cone with helical spin structure in the reciprocal space, which gives rise to spin-polarized and dissipation-less charge currents. Thanks to the nontrivial topology of the bulk electronic structure, this spin texture is robust against most types of surface defects. However, magnetic perturbations break the time-reversal symmetry, enabling magnetic scattering and loss of spin coherence of the charge carriers. This intrinsic incompatibility precludes the design of magnetoelectronic devices ...


Nonequilibrium Polarization Dynamics In Antiferroelectrics, M. M. Vopson, Xiaoli Tan Jul 2017

Nonequilibrium Polarization Dynamics In Antiferroelectrics, M. M. Vopson, Xiaoli Tan

Materials Science and Engineering Publications

A nonequilibrium statistical domain nucleation model of polarization dynamics in less understood antiferroelectric systems is introduced. Predictions of the model have been successfully tested experimentally using an antiferroelectric Pb0.99Nb0.02[( Zr0.57Sn0.43) Ti-0.94(0.06)] O-0.98(3) polycrystalline ceramic. We determined the activation energy of the domain nucleation process for this particular antiferroelectric sample to be W-b = 1.07 eV and the critical volume of the polar nucleus V * = 98 x 10(-27)m(3), which corresponds to a linear length scale of 2.86 nm.


Nematic Fluctuations And Phase Transitions In Lafeaso: A Raman Scattering Study, U. F. Kaneko, P. F. Gomes, A. F. García-Flores, J.-Q. Yan, Thomas A. Lograsso, G. E. Barberis, David Vaknin, E. Granado Jul 2017

Nematic Fluctuations And Phase Transitions In Lafeaso: A Raman Scattering Study, U. F. Kaneko, P. F. Gomes, A. F. García-Flores, J.-Q. Yan, Thomas A. Lograsso, G. E. Barberis, David Vaknin, E. Granado

Ames Laboratory Publications

Raman scattering experiments on LaFeAsO with distinct antiferromagnetic (TAFM=140 K) and tetragonal-orthorhombic (TS=155 K) transitions show a quasielastic peak (QEP) in B2g symmetry (2 Fe tetragonal cell) that fades away below ∼TAFM and is ascribed to electronic nematic fluctuations. A scaling of the reported shear modulus with the T dependence of the QEP height rather than the QEP area indicates that magnetic degrees of freedom drive the structural transition. The large separation between TS and TAFM in LaFeAsO compared to BaFe2As2 manifests itself in slower dynamics of nematic fluctuations in the former.


Thermally Activated Diffusion Of Copper Into Amorphous Carbon, David Appy, Mark Wallingford, Dapeng Jing, Ryan T. Ott, Michael C. Tringides, Gunther Richter, Patricia A. Thiel Jul 2017

Thermally Activated Diffusion Of Copper Into Amorphous Carbon, David Appy, Mark Wallingford, Dapeng Jing, Ryan T. Ott, Michael C. Tringides, Gunther Richter, Patricia A. Thiel

Ames Laboratory Accepted Manuscripts

Using x-ray photoelectron spectroscopy, the authors characterize the thermally activated changes that occur when Cu is deposited on amorphous carbon supported on Si at 300 K, then heated to 800 K. The authors compare data for Cu on the basal plane of graphite with pinning defects, where scanning tunneling microscopy reveals that coarsening is the main process in this temperature range. Coarsening begins at 500–600 K and causes moderate attenuation of the Cu photoelectron signal. For Cu on amorphous carbon, heating to 800 K causes Cu to diffuse into the bulk of the film, based on the strong attenuation ...


Crystal, Magnetic, Calorimetric And Electronic Structure Investigation Of Gdscge1–X Sb X Compounds, Francois Guillou, Arjun Pathak, T. A. Hackett, Durga Paudyal, Yaroslav Mudryk, Vitalij K. Pecharsky Jan 2017

Crystal, Magnetic, Calorimetric And Electronic Structure Investigation Of Gdscge1–X Sb X Compounds, Francois Guillou, Arjun Pathak, T. A. Hackett, Durga Paudyal, Yaroslav Mudryk, Vitalij K. Pecharsky

Ames Laboratory Accepted Manuscripts

Experimental investigations of crystal structure, magnetism and heat capacity of compounds in the pseudoternary GdScGe-GdScSb system combined with density functional theory projections have been employed to clarify the interplay between the crystal structure and magnetism in this series of RTX materials (R  =  rare-earth, $ T$   =  transition metal and X  =  p-block element). We demonstrate that the CeScSi-type structure adopted by GdScGe and CeFeSi-type structure adopted by GdScSb coexist over a limited range of compositions $0.65 \leqslant x \leqslant 0.9$ . Antimony for Ge substitutions in GdScGe result in an anisotropic expansion of the unit cell of the parent that is most ...