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Full-Text Articles in Physics

Fatigue-Resistant High-Performance Elastocaloric Materials Via Additive Manufacturing, Huilong Hou, Emrah Simsek, Tao Ma, Nathan S. Johnson, Suxin Qian, Cheikh Cissé, Drew Stasak, Naila Al Hasan, Lin Zhou, Yunho Hwang, Reinhard Radermacher, Valery I. Levitas, Matthew J. Kramer, Mohsen Asle Zaeem, Aaron P. Stebner, Ryan T. Ott, Jun Cui, Ichiro Takeuchi Aug 2019

Fatigue-Resistant High-Performance Elastocaloric Materials Via Additive Manufacturing, Huilong Hou, Emrah Simsek, Tao Ma, Nathan S. Johnson, Suxin Qian, Cheikh Cissé, Drew Stasak, Naila Al Hasan, Lin Zhou, Yunho Hwang, Reinhard Radermacher, Valery I. Levitas, Matthew J. Kramer, Mohsen Asle Zaeem, Aaron P. Stebner, Ryan T. Ott, Jun Cui, Ichiro Takeuchi

Aerospace Engineering Publications

Elastocaloric cooling, which exploits the latent heat released and absorbed as stress-induced phase transformations are reversibly cycled in shape memory alloys, has recently emerged as a frontrunner in non-vapor-compression cooling technologies. The intrinsically high thermodynamic efficiency of elastocaloric materials is limited only by work hysteresis. Here, we report on creating high-performance low-hysteresis elastocaloric cooling materials via additive manufacturing of Titanium-Nickel (Ti-Ni) alloys. Contrary to established knowledge of the physical metallurgy of Ti-Ni alloys, intermetallic phases are found to be beneficial to elastocaloric performances when they are combined with the binary Ti-Ni compound in nanocomposite configurations. The resulting microstructure gives rise ...


Energetics Of Cu Adsorption And Intercalation At Graphite Step Edges, Yong Han, Ann Lii-Rosales, Michael C. Tringides, James W. Evans, Patricia A. Thiel Mar 2019

Energetics Of Cu Adsorption And Intercalation At Graphite Step Edges, Yong Han, Ann Lii-Rosales, Michael C. Tringides, James W. Evans, Patricia A. Thiel

Chemistry Publications

To assess the energetics of Cu intercalation on defective graphite, the chemical potentials and binding energies for Cu at graphite step edges are calculated for three main configurations: an isolated atom, a chain, and an atom attached to a chain. As expected, for Cu interacting directly with a graphite step edge, the strength of interaction depends on the stability of the step, with Cu binding more strongly at a less-stable step. However, the relationship is reversed when considering binding of a Cu atom attached to a chain. Taken together, these trends mean that if the graphite step is less stable ...


Effects Of Dopants On The Glass Forming Ability In Al-Based Metallic Alloy, Yang Sun, Feng Zhang, Lin Yang, Huajing Song, Mikhail I. Mendelev, Cai-Zhuang Wang, Kai-Ming Ho Feb 2019

Effects Of Dopants On The Glass Forming Ability In Al-Based Metallic Alloy, Yang Sun, Feng Zhang, Lin Yang, Huajing Song, Mikhail I. Mendelev, Cai-Zhuang Wang, Kai-Ming Ho

Ames Laboratory Accepted Manuscripts

The effect of dopants on the metallic glass forming ability is usually considered based on the analysis of changes in the liquid structure or thermodynamics. What is missing in such considerations is an analysis of how a dopant changes the properties of the crystal phases which can form instead of the glass. In order to illuminate this aspect we performed molecular dynamics simulations to study the effects of Mg and Sm dopants on the crystal nucleation in Al. The simulation data were found to be consistent with the experimental observations that addition of Mg to Al does not lead to ...


Intercalated Rare-Earth Metals Under Graphene On Sic, Nathaniel A. Anderson, Myron Hupalo, David Keavney, Michael C. Tringides, David Vaknin Nov 2018

Intercalated Rare-Earth Metals Under Graphene On Sic, Nathaniel A. Anderson, Myron Hupalo, David Keavney, Michael C. Tringides, David Vaknin

Ames Laboratory Accepted Manuscripts

Intercalation of rare earth metals (RE = Eu, Dy, and Gd) is achieved by depositing the RE metal on graphene that is grown on silicon-carbide (SiC) and by subsequent annealing at high temperatures to promote intercalation. STM images of the films reveal that the graphene layer is defect free and that each of the intercalated metals has a distinct nucleation pattern. Intercalated Eu forms nano-clusters that are situated on the vertices of a Moirè pattern, while Dy and Gd form randomly distributed nano-clusters. X-ray magnetic circular dichroism (XMCD) measurements of intercalated films reveal the magnetic properties of these REs nano-clusters ...


Lattice Instability During Solid-Solid Structural Transformations Under A General Applied Stress Tensor: Example Of Si I → Si Ii With Metallization, Nikolai A. Zarkevich, Hao Chen, Valery I. Levitas, Duane D. Johnson Oct 2018

Lattice Instability During Solid-Solid Structural Transformations Under A General Applied Stress Tensor: Example Of Si I → Si Ii With Metallization, Nikolai A. Zarkevich, Hao Chen, Valery I. Levitas, Duane D. Johnson

Aerospace Engineering Publications

The density functional theory was employed to study the stress-strain behavior and elastic instabilities during the solid-solid phase transformation (PT) when subjected to a general stress tensor, as exemplified for semiconducting Si I and metallic Si II, where metallization precedes the PT, so stressed Si I can be a metal. The hydrostatic PT occurs at 76 GPa, while under uniaxial loading it is 11 GPa (3.7 GPa mean pressure), 21 times lower. The Si I → Si II PT is described by a critical value of the phase-field’s modified transformation work, and the PT criterion has only two parameters ...


Trends In Pressure-Induced Layer-Selective Half-Collapsed Tetragonal Phases In The Iron-Based Superconductor Family Aeafe(4)As(4), Vladislav Borisov, Paul C. Canfield, Roser Valentí Aug 2018

Trends In Pressure-Induced Layer-Selective Half-Collapsed Tetragonal Phases In The Iron-Based Superconductor Family Aeafe(4)As(4), Vladislav Borisov, Paul C. Canfield, Roser Valentí

Ames Laboratory Accepted Manuscripts

By performing pressure simulations within density functional theory for the family of iron-based superconductors AeAFe4As4 with Ae=Ca, Sr, Ba and A=K, Rb, Cs we predict in these systems the appearance of two consecutive half-collapsed tetragonal transitions at pressures Pc1 and Pc2, which have a different character in terms of their effect on the electronic structure. We find that, similar to previous studies for CaKFe4As4, spin-vortex magnetic fluctuations on the Fe sublattice play a key role for an accurate structure prediction in these materials at zero pressure. We identify clear trends of critical pressures and discuss the relevance of ...


Emergent Magnetic Degeneracy In Iron Pnictides Due To The Interplay Between Spin-Orbit Coupling And Quantum Fluctuations, Morten H. Christensen, Peter P. Orth, Brian M. Andersen, Rafael M. Fernandes Jul 2018

Emergent Magnetic Degeneracy In Iron Pnictides Due To The Interplay Between Spin-Orbit Coupling And Quantum Fluctuations, Morten H. Christensen, Peter P. Orth, Brian M. Andersen, Rafael M. Fernandes

Physics and Astronomy Publications

Recent experiments in iron pnictide superconductors reveal that, as the putative magnetic quantum critical point is approached, different types of magnetic order coexist over a narrow region of the phase diagram. Although these magnetic configurations share the same wave vectors, they break distinct symmetries of the lattice. Importantly, the highest superconducting transition temperature takes place close to this proliferation of near-degenerate magnetic states. In this Letter, we employ a renormalization group calculation to show that such a behavior naturally arises due to the effects of spin-orbit coupling on the quantum magnetic fluctuations. Formally, the enhanced magnetic degeneracy near the quantum ...


Effective Demagnetizing Factors Of Diamagnetic Samples Of Various Shapes, Ruslan Prozorov, Vladimir G. Kogan Jul 2018

Effective Demagnetizing Factors Of Diamagnetic Samples Of Various Shapes, Ruslan Prozorov, Vladimir G. Kogan

Ames Laboratory Accepted Manuscripts

Effective demagnetizing factors that connect the sample magnetic moment with the applied magnetic field are calculated numerically for perfectly diamagnetic samples of various nonellipsoidal shapes. The procedure is based on calculating the total magnetic moment by integrating the magnetic induction obtained from a full three-dimensional (3D) solution of the Maxwell equations using an adaptive mesh. The results are relevant for superconductors (and conductors in ac fields) when the London penetration depth (or the skin depth) is much smaller than the sample size. Simple but reasonably accurate approximate formulas are given for practical shapes including rectangular cuboids, finite cylinders in axial ...


Persistent Correlation Between Superconductivity And Antiferromagnetic Fluctuations Near A Nematic Quantum Critical Point In Fese1−Xsx, P. Wiecki, Khusboo Rana, A. E. Böhmer, Y. Lee, Sergey L. Bud’Ko, Paul C. Canfield, Yuji Furukawa Jul 2018

Persistent Correlation Between Superconductivity And Antiferromagnetic Fluctuations Near A Nematic Quantum Critical Point In Fese1−Xsx, P. Wiecki, Khusboo Rana, A. E. Böhmer, Y. Lee, Sergey L. Bud’Ko, Paul C. Canfield, Yuji Furukawa

Ames Laboratory Accepted Manuscripts

We present 77Se-NMR measurements on FeSe1−xSx samples with sulfur content x=0%, 9%, 15%, and 29%. Twinned nematic domains are observed in the NMR spectrum for all samples except x=29%. The NMR spin-lattice relaxation rate shows that antiferromagnetic (AFM) fluctuations are initially enhanced between x=0% and x=9%, but are strongly suppressed for higher x values. The observed behavior of the AFM fluctuations parallels the superconducting transition temperature Tc in these materials, providing strong evidence for the primary importance of AFM fluctuations for superconductivity, despite the presence of nematic quantum criticality in the FeSe1−xSx system.


Current Progress And Future Challenges In Rare-Earth-Free Permanent Magnets, Jun Cui, Matthew J. Kramer, Lin Zhou, Fei Liu, Alexander Gabay, George Hadjipanayis, Balamurugan Balasubramanian, David Sellmyer Jul 2018

Current Progress And Future Challenges In Rare-Earth-Free Permanent Magnets, Jun Cui, Matthew J. Kramer, Lin Zhou, Fei Liu, Alexander Gabay, George Hadjipanayis, Balamurugan Balasubramanian, David Sellmyer

Ames Laboratory Accepted Manuscripts

Permanent magnets (PM) are critical components for electric motors and power generators. Key properties of permanent magnets, especially coercivity and remanent magnetization, are strongly dependent on microstructure. Understanding metallurgical processing, phase stability and microstructural changes are essential for designing and improving permanent magnets. The widely used PM for the traction motor in electric vehicles and for the power generator in wind turbines contain rare earth elements Nd and Dy due to their high maximum energy product. Dy is used to sustain NdFeB's coercivity at higher temperature. Due to the high supply risk of rare earth elements (REE) such as ...


Magnetic Phase Diagram Of The Iron Pnictides In The Presence Of Spin-Orbit Coupling: Frustration Between C2 And C4 Magnetic Phases, Morten H. Christensen, Peter P. Orth, Brian M. Andersen, Rafael M. Fernandes Jul 2018

Magnetic Phase Diagram Of The Iron Pnictides In The Presence Of Spin-Orbit Coupling: Frustration Between C2 And C4 Magnetic Phases, Morten H. Christensen, Peter P. Orth, Brian M. Andersen, Rafael M. Fernandes

Physics and Astronomy Publications

We investigate the impact of spin anisotropic interactions, promoted by spin-orbit coupling, on the magnetic phase diagram of the iron-based superconductors. Three distinct magnetic phases with Bragg peaks at (π,0) and (0,π) are possible in these systems: one C2 (i.e. orthorhombic) symmetric stripe magnetic phase and two C4 (i.e. tetragonal) symmetric magnetic phases. While the spin anisotropic interactions allow the magnetic moments to point in any direction in the C2 phase, they restrict the possible moment orientations in the C4 phases. As a result, an interesting scenario arises in which the spin anisotropic interactions favor a ...


Influence Of The Starting Temperature Of Calorimetric Measurements On The Accuracy Of Determined Magnetocaloric Effect, L. M. Moreno-Ramírez, V. Franco, A. Conde, H. Neves Bez, Yaroslav Mudryk, Vitalij K. Pecharsky Jul 2018

Influence Of The Starting Temperature Of Calorimetric Measurements On The Accuracy Of Determined Magnetocaloric Effect, L. M. Moreno-Ramírez, V. Franco, A. Conde, H. Neves Bez, Yaroslav Mudryk, Vitalij K. Pecharsky

Ames Laboratory Accepted Manuscripts

Availability of a restricted heat capacity data range has a clear influence on the accuracy of calculated magnetocaloric effect, as confirmed by both numerical simulations and experimental measurements. Simulations using the Bean-Rodbell model show that, in general, the approximated magnetocaloric effect curves calculated using a linear extrapolation of the data starting from a selected temperature point down to zero kelvin deviate in a non-monotonic way from those correctly calculated by fully integrating the data from near zero temperatures. However, we discovered that a particular temperature range exists where the approximated magnetocaloric calculation provides the same result as the fully integrated ...


A Self-Contained Algorithm For Determination Of Solid-Liquid Equilibria In An Alloy System, L. Yang, Y. Sun, Z. Ye, F. Zhang, M. I. Mendelev, Cai-Zhuang Wang, Kai-Ming Ho Jul 2018

A Self-Contained Algorithm For Determination Of Solid-Liquid Equilibria In An Alloy System, L. Yang, Y. Sun, Z. Ye, F. Zhang, M. I. Mendelev, Cai-Zhuang Wang, Kai-Ming Ho

Ames Laboratory Accepted Manuscripts

We describe a self-contained procedure to evaluate the free energy of liquid and solid phases of an alloy system. The free energy of a single-element solid phase is calculated with thermodynamic integration using the Einstein crystal as the reference system. Then, free energy difference between the solid and liquid phases is calculated by Gibbs-Duhem integration. The central part of our method is the construction of a reversible alchemical path connecting a pure liquid and a liquid alloy to calculate the mixing enthalpy and entropy. We have applied the method to calculate the free energy of solid and liquid phases in ...


Two-Dimensional Crystallization Of Poly(N-Isopropylacrylamide)-Capped Gold Nanoparticles, Wenjie Wang, Jack J. Lawrence, Wei Bu, Honghu Zhang, David Vaknin Jun 2018

Two-Dimensional Crystallization Of Poly(N-Isopropylacrylamide)-Capped Gold Nanoparticles, Wenjie Wang, Jack J. Lawrence, Wei Bu, Honghu Zhang, David Vaknin

Ames Laboratory Accepted Manuscripts

Surface-sensitive X-ray reflectivity and grazing incidence small-angle X-ray scattering reveal the structure of polymer-capped-gold nanoparticles (AuNPs that are grafted with poly(N-isopropylacrylamide); PNIPAM–AuNPs) as they self-assemble and crystallize at the aqueous suspension/vapor interface. Citrate-stabilized AuNPs (5 and 10 nm in nominal diameter) are ligand-exchanged by 6 kDa PNIPAM-thiol to form corona brushes around the AuNPs that are highly stable and dispersed in aqueous suspensions. Surprisingly, no clear evidence of thermosensitive effect on surface enrichment or self-assembly of the PNIPAM–AuNPs is observed in the 10–35 °C temperature range. However, addition of simple salts (in this case ...


First-Principles Study Of Electronic Structure And Fermi Surface In Semimetallic Yas, Przemyslaw Swatek Jun 2018

First-Principles Study Of Electronic Structure And Fermi Surface In Semimetallic Yas, Przemyslaw Swatek

Ames Laboratory Accepted Manuscripts

In the course of searching for new systems, which exhibit nonsaturating and extremely large positive magnetoresistance, electronic structure, Fermi surface, and de Haas-van Alphen characteristics of the semimetallic YAs compound were studied using the all-electron full-potential linearized augmented-plane wave (FP-LAPW) approach in the framework of the generalized gradient approximation (GGA). In the scalar-relativistic calculation, the cubic symmetry splits fivefold degenerate Y-d orbital into low-energy threefold-degenerate t(2g) and twofold degenerate doublet e(1g) states at Gamma point around the Fermi energy. One of them, together with the threefold degenerate t(1u) character of As-p orbital, render the YAs semimetal with ...


Anisotropic Magnetocaloric Response In Alfe2b2, R. Barua, B. T. Lejeune, Liqin Ke, G. Hadjipanayis, Eugene M. Levin, Mccallum Consulting Llc, Matthew J. Kramer, L. H. Lewis May 2018

Anisotropic Magnetocaloric Response In Alfe2b2, R. Barua, B. T. Lejeune, Liqin Ke, G. Hadjipanayis, Eugene M. Levin, Mccallum Consulting Llc, Matthew J. Kramer, L. H. Lewis

Ames Laboratory Accepted Manuscripts

Experimental investigations of the magnetocaloric response of the intermetallic layered AlFe2B2 compound along the principle axes of the orthorhombic cell were carried out using aligned plate-like crystallites with an anisotropic [101] growth habit. Results were confirmed to be consistent with density functional theory calculations. Field-dependent magnetization data confirm that the a-axis is the easy direction of magnetization within the (ac) plane. The magnetocrystalline anisotropy energy required to rotate the spin quantization vector from the c-to the a-axis direction is determined as K∼0.9 MJ/m3 at 50 K. Magnetic entropy change curves measured near the Curie transition temperature of ...


Nmr Studies Of The Helical Antiferromagnetic Compound Euco2p2, N. Higa, Qing-Ping Ding, F. Kubota, H. Uehara, M. Yogi, Yuji Furukawa, N. S. Sangeetha, David C. Johnston, A. Nakamura, M. Hedo, T. Nakama, Y. Onuki May 2018

Nmr Studies Of The Helical Antiferromagnetic Compound Euco2p2, N. Higa, Qing-Ping Ding, F. Kubota, H. Uehara, M. Yogi, Yuji Furukawa, N. S. Sangeetha, David C. Johnston, A. Nakamura, M. Hedo, T. Nakama, Y. Onuki

Ames Laboratory Accepted Manuscripts

In EuCo2P2, 4f electron spins of Eu2+ ions order antiferromagnetically below a Néel temperature . The magnetic structure below was reported to be helical with the helix axis along the c-axis from the neutron diffraction study. We report the results of 153Eu, 59Co and 31P nuclear magnetic resonance (NMR) measurements on EuCo2P2 using a single crystal and a powdered sample. In the antiferromagnetic (AFM) state, we succeeded in observing 153Eu, 59Co and 31P NMR spectra in zero magnetic field. The sharp 153Eu zero field NMR (ZF NMR) lines indicate homogeneous Eu ordered moment. The 59Co and 31P ZF NMR spectra showed ...


Enhanced Moments Of Eu In Single Crystals Of The Metallic Helical Antiferromagnet Euco2-Yas2, N. S. Sangeetha, V. K. Anand, Eduardo Cuervo-Reyes, V. Smetana, A.-V. Mudring, David C. Johnston Apr 2018

Enhanced Moments Of Eu In Single Crystals Of The Metallic Helical Antiferromagnet Euco2-Yas2, N. S. Sangeetha, V. K. Anand, Eduardo Cuervo-Reyes, V. Smetana, A.-V. Mudring, David C. Johnston

Ames Laboratory Accepted Manuscripts

The compound EuCo2-yAs2 with the tetragonal ThCr2Si2 structure is known to contain Eu+2 ions with spin S = 7/2 that order below a temperature T-N approximate to 47 K into an antiferromagnetic (AFM) proper helical structure with the ordered moments aligned in the tetragonal ab plane, perpendicular to the helix axis along the c axis, with no contribution from the Co atoms. Here we carry out a detailed investigation of the properties of single crystals. We consistently find about 5% vacancies on the Co site from energy-dispersive x-ray analysis and x-ray diffraction refinements. Enhanced ordered and effective moments of ...


Interplay Of Conventional With Inverse Electrocaloric Response In (Pb,Nb) (Zr,Sn,Ti)O3 Antiferroelectric Materials, Nikola Novak, Florian Weyland, Satyanarayan Patel, Hanzheng Guo, Xiaoli Tan, Jürgen Rödel, Jurij Koruza Mar 2018

Interplay Of Conventional With Inverse Electrocaloric Response In (Pb,Nb) (Zr,Sn,Ti)O3 Antiferroelectric Materials, Nikola Novak, Florian Weyland, Satyanarayan Patel, Hanzheng Guo, Xiaoli Tan, Jürgen Rödel, Jurij Koruza

Materials Science and Engineering Publications

The electrocaloric effect in ferroics is considered a powerful solid-state cooling technology. Its potential is enhanced by correlation to the inverse electrocaloric effect and leads into mechanisms of decreasing or increasing dipolar entropy under applied electric field. Nevertheless, the mechanism underlying the increase of the dipolar entropy with applied electric field remains unclear and controversial. This study investigates the electrocaloric response of the antiferroelectric Pb0.99Nb0.02[(Zr0.58Sn0.43)0.92 Ti0.08]0.98O3 in which the critical electric field is low enough to induce the ferroelectric phase over a broad temperature range. Utilizing temperature- and electric-field-dependent dielectric ...


Defect-Mediated, Thermally-Activated Encapsulation Of Metals At The Surface Of Graphite, Yinghui Zhou, Ann Lii-Rosales, Minsung Kim, Mark Wallingford, Dapeng Jing, Michael C. Tringides, Cai-Zhuang Wang, Patricia A. Thiel Feb 2018

Defect-Mediated, Thermally-Activated Encapsulation Of Metals At The Surface Of Graphite, Yinghui Zhou, Ann Lii-Rosales, Minsung Kim, Mark Wallingford, Dapeng Jing, Michael C. Tringides, Cai-Zhuang Wang, Patricia A. Thiel

Chemistry Publications

We show that 3 metals – Dy, Ru, and Cu – can form multilayer intercalated (encapsulated) islands at the graphite (0001) surface if 2 specific conditions are met: Defects are introduced on the graphite terraces to act as entry portals, and the metal deposition temperature is well above ambient. Focusing on Dy as a prototype, we show that surface encapsulation is much different than bulk intercalation, because the encapsulated metal takes the form of bulk-like rafts of multilayer Dy, rather than the dilute, single-layer structure known for the bulk compound. Carbon-covered metallic rafts even form for relatively unreactive metals (Ru and Cu ...


Quantum Tricritical Point In The Temperature-Pressure-Magnetic Field Phase Diagram Of Cetige3, Udhara S. Kaluarachchi, Valentin Taufor, Sergey Bud’Ko, Paul C. Canfield Jan 2018

Quantum Tricritical Point In The Temperature-Pressure-Magnetic Field Phase Diagram Of Cetige3, Udhara S. Kaluarachchi, Valentin Taufor, Sergey Bud’Ko, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

We report the temperature-pressure-magnetic-field phase diagram of the ferromagnetic Kondo-lattice CeTiGe 3 determined by means of electrical resistivity measurements. Measurements up to ∼ 5.8 GPa reveal a rich phase diagram with multiple phase transitions. At ambient pressure, CeTiGe 3 orders ferromagnetically at T C = 14 K. Application of pressure suppresses T C , but a pressure-induced ferromagnetic quantum criticality is avoided by the appearance of two new successive transitions for p > 4.1 GPa that are probably antiferromagnetic in nature. These two transitions are suppressed under pressure, with the lower-temperature phase being fully suppressed above 5.3 GPa. The critical pressures ...


Nodeless Superconductivity In Type-Ii Dirac Semimetal Pdte2: Low-Temperature London Penetration Depth And Symmetry Analysis, Seram Teknowijoyo, Na Hyun Jo, Mathias S. Scheurer, Makariy A. Tanatar, Kyuil Cho, Sergey L. Bud’Ko, Peter Orth, Paul C. Canfield, Ruslan Prozorov Jan 2018

Nodeless Superconductivity In Type-Ii Dirac Semimetal Pdte2: Low-Temperature London Penetration Depth And Symmetry Analysis, Seram Teknowijoyo, Na Hyun Jo, Mathias S. Scheurer, Makariy A. Tanatar, Kyuil Cho, Sergey L. Bud’Ko, Peter Orth, Paul C. Canfield, Ruslan Prozorov

Physics and Astronomy Publications

Superconducting gap structure was probed in type-II Dirac semimetal PdTe2 by measuring the London penetration depth using tunnel diode resonator technique. At low temperatures, the data for two samples are well described by weak coupling exponential fit yielding λ(T=0)=230~nm as the only fit parameter at a fixed Δ(0)/Tc≈1.76, and the calculated superfluid density is consistent with a fully gapped superconducting state characterized by a single gap scale. Electrical resistivity measurements for in-plane and inter-plane current directions find very low and nearly temperature-independent normal- state anisotropy. The temperature dependence of resistivity is typical ...


Magnetic Properties Of Single Crystalline Itinerant Ferromagnet Alfe2b2, Tey Lamichhane, Li Xiang, Qisheng Lin, Tribhuwan Pandey, David S. Parker, Tae-Hoon Kim, Lin Zhou, Matthew J. Kramer, Sergey L. Bud’Ko, Paul C. Canfield Jan 2018

Magnetic Properties Of Single Crystalline Itinerant Ferromagnet Alfe2b2, Tey Lamichhane, Li Xiang, Qisheng Lin, Tribhuwan Pandey, David S. Parker, Tae-Hoon Kim, Lin Zhou, Matthew J. Kramer, Sergey L. Bud’Ko, Paul C. Canfield

Ames Laboratory Publications

No abstract provided.


Phase Transitions And Their Interaction With Dislocations In Silicon, Valery I. Levitas, Hao Chen, Liming Xiong Jan 2018

Phase Transitions And Their Interaction With Dislocations In Silicon, Valery I. Levitas, Hao Chen, Liming Xiong

Aerospace Engineering Publications

In this paper, phase transformations (PTs) in silicon were investigated through molecular dynamics (MD) using Tersoff potential. In the first step, simulations of PTs in single crystal silicon under various stress-controlled loading were carried out. Results shows that all instability points under various stress states are described by criteria, which are linear in the space of normal stresses. There is a region in the stress space in which conditions for direct and reverse PTs coincide and a unique homogeneous phase transition (without nucleation) can be realized. Finally, phase transition in bi-crystalline silicon with a dislocation pileup along the grain boundary ...


Novel Mechanisms For Solid-State Processing And Grain Growth With Microstructure Alignment In Alnico-8 Based Permanent Magnets, Aaron G. Kassen, Emma M. H. White, Liangfa Hu, Wei Tang, Lin Zhou, Matthew J. Kramer, Iver E. Anderson Jan 2018

Novel Mechanisms For Solid-State Processing And Grain Growth With Microstructure Alignment In Alnico-8 Based Permanent Magnets, Aaron G. Kassen, Emma M. H. White, Liangfa Hu, Wei Tang, Lin Zhou, Matthew J. Kramer, Iver E. Anderson

Ames Laboratory Accepted Manuscripts

An estimated 750,000 new hybrid electric and plug-in battery vehicles, most with permanent magnet synchronous alternating current (PMAC) drive motors, took to the road in 2016 alone. Accompanied by 40% year over year growth in the EV market significant challenges exist in producing large quantities of permanent magnets (on the order of tens of millions) for reliable, low-cost traction motors [IE Agency, Energy Technology Perspectives (2017)]. Since the rare earth permanent magnet (REPM) market is essentially 100% net import reliant in the United States and has proven to have an unstable cost and supply structure in recent years, a ...


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 ...


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 ...


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 ...


Effect Of Molybdenum Incorporation On The Structure And Magnetic Properties Of Cobalt Ferrite, C. Orozco, A. Melendez, S. Manadhar, S. R. Singamaneni, Kongara M. Reddy, Kinjal H. Gandha, I. C. Niebedim, C. V. Ramana Jan 2017

Effect Of Molybdenum Incorporation On The Structure And Magnetic Properties Of Cobalt Ferrite, C. Orozco, A. Melendez, S. Manadhar, S. R. Singamaneni, Kongara M. Reddy, Kinjal H. Gandha, I. C. Niebedim, C. V. Ramana

Ames Laboratory Accepted Manuscripts

We report on the effect of molybdenum (Mo) incorporation on the crystal structure, surface morphology, Mo chemical valence state, and magnetic properties of cobalt ferrite (CoFe2O4, referred to CFO). Molybdenum incorporated cobalt ferrite (CoFe2–xMoxO4, referred to CFMO) ceramics were prepared by the conventional solid-state reaction method by varying the Mo concentration in the range of x = 0.0–0.3. X-ray diffraction studies indicate that the CFMO materials crystallize in inverse spinel cubic phase. Molybdenum incorporation induced lattice parameter increase from 8.322 to 8.343 Å coupled with a significant increase in density from 5 ...


Half-Metallic Co-Based Quaternary Heusler Alloys For Spintronics: Defect- And Pressure-Induced Transitions And Properties, Enamullah, D. D. Johnson, K. G. Suresh, Aftab Alam Nov 2016

Half-Metallic Co-Based Quaternary Heusler Alloys For Spintronics: Defect- And Pressure-Induced Transitions And Properties, Enamullah, D. D. Johnson, K. G. Suresh, Aftab Alam

Ames Laboratory Publications

Heusler compounds offer potential as spintronic devices due to their spin polarization and half-metallicity properties, where electron spin-majority (minority) manifold exhibits states (band gap) at the electronic chemical potential, yielding full spin polarization in a single manifold. Yet, Heuslers often exhibit intrinsic disorder that degrades its half-metallicity and spin polarization. Using density-functional theory, we analyze the electronic and magnetic properties of equiatomic Heusler (L21) CoMnCrAl and CoFeCrGe alloys for effects of hydrostatic pressure and intrinsic disorder (thermal antisites, binary swaps, and vacancies). Under pressure, CoMnCrAl undergoes a metallic transition, while half-metallicity in CoFeCrGe is retained for a limited range. Antisite ...