Personnel

Overview

Publications

Personnel

Overview

This project focuses on low dimensional surface structures (ultrathin metallic films, islands, wires, etc.), especially in systems exhibiting quantum size effects (QSE). Since such structures are metastable and grown far from equilibrium, it is important to identify the optimal kinetic pathways. In turn, this requires a better understanding of many atomistic processes (e.g. surface diffusion, nucleation, coarsening) that define the kinetic pathway. In addition the properties of the grown structures (e.g. band structure, density-of-states) depend on the structure dimensions. This opens the possibility to control their potential uses in chemical reactivity and energy storage.

This interdisciplinary effort (physics, chemistry) is built upon a close interaction between theorists (Wang, Ho) and experimentalists (Tringides, Thiel, Hupalo). The scientists with the project have a strong background in film growth, coarsening, diffusion, nucleation, and overlayer structure analysis.

This projects objectives include:

  • Kinetics of growth. Certain systems with QSE exhibit anomalously fast aggregation kinetics, i.e. deposited atoms assemble very quickly into islands. We study and model the “window” in temperature and coverage parameter space where QSE-driven self organization is possible. These data are modeled to extract the controlling barriers. This understanding will be used to search for other systems where height uniformity exists.
  • QSE and chemisorption. We test the effect of QSE on chemisorption in several systems, using both experiment (STM/STS, XPS, HRLEED) and theory. These systems include oxygen and hydrocarbons on Ag nanostructures on Si(111); and oxygen and hydrogen on Pb and Mg nanostructures.

Highlights

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Publications

2009
Unal B; Fournee V; Thiel P A; Evans J W . 2009. Structure and Growth of Height-Selected Ag Islands on Fivefold i-AlPdMn Quasicrystalline Surfaces: STM Analysis and Step Dynamics Modeling. Physical Review Letters. 102:196103. abstract
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Binz S M; Hupalo M; Tringides M C . 2009. Quantum size effect dependent critical size cluster and finite size effects. Journal of Applied Physics. 105:094307. abstract
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Thiel P A; Shen M; Liu D J; Evans J W . 2009. Coarsening of Two-Dimensional Nanoclusters on Metal Surfaces. Journal of Physical Chemistry C. 113:5047-5067. abstract
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Shen M M; Liu D J; Jenks C J; Thiel P A; Evans J W . 2009. Accelerated coarsening of Ag adatom islands on Ag(111) due to trace amounts of S: Mass-transport mediated by Ag-S complexes. Journal of Chemical Physics. 130:094701. abstract
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Li M; Wang C Z; Evans J W; Hupalo M; Tringides M C; Ho K M . 2009. Competition between area and height evolution of Pb islands on a Si(111) surface. Physical Review B. 79:113404. abstract
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2008
Man K L; Tringides M C; Loy M M T; Altman M S . 2008. Anomalous Mass Transport in the Pb Wetting Layer on the Si(111) Surface. Physical Review Letters. 101:226102. abstract
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Binz S M; Hupalo M; Tringides M C . 2008. Height-dependent nucleation and ideal layer by layer growth in Pb/Pb(111)/Si(111). Physical Review B. 78:193407. abstract
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Kuntova Z; Tringides M C; Chvoj Z . 2008. Height-dependent barriers and nucleation in quantum size effect growth. Physical Review B. 78:155431. abstract
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Personnel

Postdoctoral Research Associates:

Overview

This project concentrates on developing quantitative, self-consistent structural descriptions of liquid and amorphous states in metallic systems. Our research moves beyond static structural descriptions towards a detailed thermodynamic understanding of liquid and amorphous states, consistent with structural models. Binary alloys are emphasized to more accurately describe local structure. Moreover, the capabilities of the Materials Preparation Center are utilized to synthesize high-purity alloys having precise composition control. Experimental methods, atomistic simulations, and fundamental theoretical predictions are integrated for the measurement of structure, chemistry, and macroscopic thermodynamic properties in selected liquid and amorphous Al- and Zr-based model systems.

This project utilizes DOE-supported x-ray and neutron sources to capture structural- and chemically-specific details about short- and medium-range order in disordered systems. In addition, targeted scattering data are used to support efforts to develop highly accurate inter-atomic potentials. Simulation approaches include ab initio, constrained reverse Monte Carlo, and classical molecular dynamics using both pair-wise and, more importantly, many-body inter-atomic potentials, including tight-binding and embedded-atom method approaches. A new "embedded-cluster" method for ab initio calculations is pursued to mitigate the artifacts created by periodic boundary conditions of conventional first-principles methods. Combined with experimental data, simulations ultimately allow us to predict—e.g., changes in temperature, strain, or composition—alterations in local and long-range atomic ordering, leading to different disordered structures or perhaps highly-correlated phase transformations.

Highlights

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Publications

2008
Fortini A; Mendelev M I; Buldyrev S; Srolovitz D . 2008. Asperity contacts at the nanoscale: Comparison of Ru and Au. Journal of Applied Physics. 104:074320. abstract
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Fang J X; Kong P; Ding B J; Song X P; Han Y; Hahn H; Gleiter H . 2008. Single crystal growth via a grain rotation mechanism within amorphous matrix. Applied Physics Letters. 93:153115. abstract
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Bednarcik J; Venkataraman S; Khvostikova O; Franz H; Sordelet D J; Eckert J . 2008. Microstructural changes induced by thermal treatment in Cu47Ti33Zr11Ni8Si1 metallic glass. Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing. 498:335-340. abstract
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Personnel

Postdoctoral Research Associates:

Overview

This project develops and applies advanced solid-state nuclear magnetic resonance (NMR) techniques to elucidate the structure and dynamics of complex organic, nanocomposite, and semiconductor materials. Systems of particular interest include bioinspired nanocomposites (in collaboration with the Project on Bioinspired Materials), nanostructured polymer-based fuel-cell membranes, and complex tellurides for photovoltaics, data storage, and thermoelectrics (in collaboration with Bruce Cook, Ames Laboratory).

We study nanocomposites of Nafion with modified side groups and with silica or zirconium phosphate nanoparticles grown in situ, developed to improve fuel-cell operation at higher temperatures. This extends our investigations to the biological nanocomposites in enamel and biosilicas.

Highlights

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Publications

2008
Kanapathipillai M; Yusufoglu Y; Rawal A; Hu Y Y; Lo C T; Thiyaigarajan P; Kalay Y E; Akinc M; Mallapragada S; Schmidt-Rohr K . 2008. Synthesis and characterization of ionic block copolymer templated calcium phosphate nanocomposites. Chemistry of Materials. 20:5922-5932. abstract
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Rawal A; Wei X; Akinc A; Schmidt-Rohr K . 2008. Dispersion of silicate in tricalcium phosphate elucidated by solid-state NMR. Chemistry of Materials. 20:2583-2591. abstract
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Personnel

Overview

The goal of this project is to learn to control the flow of light and the conversion of light energy into other forms of energy (and vice versa). This project is fundamental physics research that supports the mission of DOE in the areas of energy-efficient lighting, efficient solar energy utilization, and thermophotovoltaics. Research in this Project can be grouped into two sub-tasks.

Photonic Crystal Physics
Photonic band gap materials are artificially designed periodic dielectric or metallic structures with high refractive-index contrast that can be used to control light (photons) in a manner similar to that used by semiconductors to control electrons. Although this research project originated from theoretical work, its emphasis now is on physical manifestations and tests of the theory. Over the next three years research goals within this subtask will focus on:

  • Wide area fabrication of photonic crystal and polymer waveguide structures using reasonable-cost soft lithography techniques (K. Constant, W. Leung, K.-M. Ho).
  • Study of fundamental photonic crystal properties including tailored thermal emission, beam steering and focusing (R. Biswas, K. Constant, C. Soukoulis, W. Leung, K.-M. Ho).
  • Development of highly efficient algorithms for design and study of devices using photonic crystals. Extension of techniques to study non-linear systems or systems with gain as well as the effects of disorder/fabrication defects on the performance of photonic crystal structures. (C. Soukoulis, K.-M. Ho)

Organic Semiconductor Physics
The goal of this subtask is to provide the fundamental physics underpinning necessary to understand and optimize the performance of organic light-emitting devices (OLEDs) at both low and high brightness. More specifically, the goal is to elucidate the interactions (particularly the spin-dependent interactions) between singlet excitons (SEs), triplet excitons (TEs), polarons, bipolarons, and trions, as they impact the optical and transport properties of these materials and devices. For example, our past experimental work has revealed the central role of TEs and polarons in quenching the SEs, thus decreasing the photoluminescence quantum yield of the films and the internal quantum efficiency of OLEDs. Indeed, these quenching processes are now recognized as the source of the decreasing efficiency of OLEDs at high injection current.

Over the next three years research within this subtask will focus on fundamental studies on novel OLED structures, including n-stacked (tandem) OLEDs, graded junction OLEDs, and hybrid polymer/small molecular OLEDs. (J. Shinar).

Highlights

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Publications

2008
Kohli P; Chatterton J; Stieler D; Tuttle G; Li M; Hu X H; Ye Z; Ho K M . 2008. Fine tuning resonant frequencies for a single cavity defect in three-dimensional layer-by-layer photonic crystal. Optics Express. 16:19844-19849. abstract
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Dai W; Soukoulis C M . 2008. Converging and wave guiding of Gaussian beam by two-layer dielectric rods. Applied Physics Letters. 93:201101. abstract
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Biswas R; Christensen C; Muehlmeier J; Tuttle G; Ho K M . 2008. Waveguide circuits in three-dimensional photonic crystals. Photonics and Nanostructures-Fundamentals and Applications. 6:134-141. abstract
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Personnel

Overview

The growth, control and modification of novel materials in single crystal and polycrystalline form, represent a national core competency that is essential for scientific advancement within and across traditional disciplinary boundaries, and are critical components of the USDOE Basic Energy Sciences' mission. In support of this mission, the Novel Materials Preparation and Processing Methodologies project strengthens the materials synthesis efforts of the Ames Laboratory.

The objectives of Novel Materials Preparation are to quantify and control processing-structure-property relationships: the basic science of how chemical inhomogeneities and structural defects affect properties of highly responsive materials; advance the ability to synthesize and characterize high purity, high quality materials, primarily in single crystal form; develop unique capabilities and processing knowledge in the preparation, purification, and fabrication of metallic elements and alloys.

Our efforts are grouped into three areas:

  1. growth-based activities that have focused on identifying the operating limits for solution growth methods by defining stable growth regimes,
  2. materials-focused investigations of highly responsive materials systems where synthesis challenges often limit the science and where careful control of synthesis structure relations are vital for understanding materials behavior,
  3. development of single crystals facilities that broaden and enhance our growth capabilities to address a wider range of materials.

In addition, the Materials Preparation Center, a specialized research center managed through the BES Synthesis & Processing core research area, provide high-purity, high-quality, and well-characterized materials in support of scientific research programs at the Ames Laboratory the general scientific community.

Highlights

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Publications

2008
Cao H; Bai F M; Li J F; Viehland D D; Lograsso T A; Gehring P M . 2008. Structural studies of decomposition in Fe-x at.%Ga alloys. Journal of Alloys and Compounds. 465:244-249. abstract
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Mihalkovic M; Francoual S; Shibata K; De Boissieu M; Baron A Q R; Sidis Y; Ishimasa T; Wu D; Lograsso T; Regnault L P; Gahler F; Tsutsui S; Hennion B; Bastie P; Sato T J; Takakura H; Currat R; Tsai A P . 2008. Atomic dynamics of i-ScZnMg and its 1/1 approximant phase: Experiment and simulation. Philosophical Magazine. 88:2311-2318. abstract
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Pussi K; Reid D E; Ferralis N; McGrath R; Lograsso T A; Ross A R; Diehl R D . 2008. Low-energy electron diffraction (LEED) study of an aperiodic thin film of Cu on 5-fold i-Al-Pd-Mn. Philosophical Magazine. 88:2103-2110. abstract
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Personnel

Postdoctoral Research Associates:

Overview

This project is designed to meet the challenge of synthesizing and characterizing new magnetic materials whose basic unit is of nanometer size. This Project will expand the coordinated efforts of recent years in the synthesis and characterization of magnetic molecules so as to target a wider array of nanoscale magnetic systems. Strong collaborative ties with scientists at national and international institutions and facilities enhance the Ames effort. In-house experimental facilities probe spin interactions (when necessary down to millikelvin temperatures) by NMR, fast optics, x-ray, susceptibility, and neutron scattering techniques. This project also includes a strong theory component using analytical methods, classical and quantum simulation tools, and first-principles electronic structure methods.

Subtasks in this project are:

  • Magnetic molecules. An established centerpiece of this entire Project is the study of single crystals composed of nanometer-size magnetic molecules. In future work we will manipulate the synthesis process so as to systematically track the emergence of cooperative, macroscopic magnetic phenomena in 1, 2, and 3 dimensions for a matrix of nano-size building blocks. We will also expand our study of quasi-one-dimensional (1D) and 2D magnets, where the magnetic entities have a nanoscale dimension in two and one dimensions, respectively. The above systems include magnetic geometries leading to spin frustration, a novel state of matter. (M. Luban, Y. Furukawa, D. Johnston, R. Prozorov, V. Dobrovitski, D. Vaknin, J. Zaretsky, B. Harmon). Formal collaborations exist with Paul Koegerler (Jülich) and Christian Schröder (Bielefeld)
  • Single and few spin systems. Investigations of single-spin and few-spin quantum dynamics, in such nanostructures as quantum dots and spin impurity centers in crystals, will help to understand the environmental interactions affecting spin systems and will lead to ways for controlling and suppressing the decoherence of spins in nanostructures. Powerful and accurate numerical techniques, together with modern analytical approaches will be used. Experimentally, fast optical probes will be used to detect and coherently manipulate spin coherence, and assess and control relaxation. Advanced spin resonance techniques will also be employed. (V. Dobrovitski, B. Harmon, Y. Furukawa)
  • Magnetic nanostructures on surfaces. This subtask will use a different approach for self-assembly and the creation of nanoscale spin systems. Magnetic species will be deposited on graphene (for optimal mobility and limited chemical activity), and island formation monitored. Magnetic STM tips will be used to probe the magnetism distribution on the island, and fast probe optical Kerr effects will explore the dynamics. Spin polarized first principles electronic structure calculations will be used to investigate the quantum size effect and magnetic response. (M. Tringides, M. Hupalo, C.-Z. Wang)

Highlights

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Publications

2009
Fielden J; Quasdorf K; Ellern A; Kogerler P . 2009. A Homochiral 2D Copper(II) Coordination Framework. European Journal of Inorganic Chemistry. :717-720. abstract
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Rousochatzakis I; Lauchli A; Borsa F; Luban M . 2009. Theory of severe slowdown in the relaxation of rings and clusters with antiferromagnetic interactions. Physical Review B. 79:064421. abstract
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Fang X; Kogerler P; Lsaacs L; Uchida S; Mizuno N . 2009. Cucurbit[n]uril-Polyoxoanion Hybrids. Journal of the American Chemical Society. 131:432-+. abstract
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Engelhardt L; Martin C; Prozorov R; Luban M; Timco G A; Winpenny R E P . 2009. High-field magnetic properties of the magnetic molecule {Cr10Cu2}. Physical Review B. 79:014404. abstract
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Todea A M; Merca A; Bogge H; Glaser T; Engelhardt L; Prozorov R; Lubanc M; Muller A . 2009. Polyoxotungstates now also with pentagonal units: supramolecular chemistry and tuning of magnetic exchange in {(M)M-5}(12)V-30 Keplerates (M = Mo, W). Chemical Communications. :3351-3353. abstract
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2008
Liu C; Samolyuk G D; Lee Y; Ni N; Kondo T; Santander-Syro A F; Bud'ko S L; McChesney J L; Rotenberg E; Valla T; Fedorov A V; Canfield P C; Harmon B N; Kaminski A . 2008. K-Doping Dependence of the Fermi Surface of the Iron-Arsenic Ba1-xKxFe2As2 Superconductor Using Angle-Resolved Photoemission Spectroscopy. Physical Review Letters. 101:177005. abstract
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Fang X K; Kogerler P . 2008. PO43--Mediated Polyoxometalate Supercluster Assembly. Angewandte Chemie-International Edition. 47:8123-8126. abstract
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Personnel

Postdoctoral Research Associates:

Overview

The objective of this project is to obtain a better understanding of the physics of metamaterials, particularly left-handed materials. This project collectively has been, and continues to be, a prime mover and initiator of the development of left-handed materials, characterized by a negative index of refraction. This revolutionary concept originally prompted objections, based on perceived violations of causality, momentum conservation, and Fermat’s principle. This controversy is now settled, mainly through the work of this project, clearing the way for the following objectives to be addressed.

The work in this project will have deep impact on the BES Grand Challenge "how do we design and perfect atom- and energy-efficient syntheses of revolutionary new forms of matter with tailored properties?" and in current optical technologies, such as nanophotonics, optical communications, optical imaging, and optical circuitry. In addition, the novel nanofabrication and advanced characterization techniques involved in this program can be readily transferred to other DOE-related programs.

Highlights

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Publications

2009
Diem M; Koschny T; Soukoulis C M . 2009. Wide-angle perfect absorber/thermal emitter in the terahertz regime. Physical Review B. 79:033101. abstract
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2008
Soukoulis C M . 2008. Bending Back Light: The Science of Negative Index Materials. Proceedings of the 2008 International Workshop on Metamaterials. :4-5411. abstract
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Wegener M; Garcia-Pomar J L; Soukoulis C M; Meinzer N; Ruther M; Linden S . 2008. Toy model for plasmonic metamaterial resonances coupled to two-level system gain. Optics Express. 16:19785-19798. abstract
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Dai W; Soukoulis C M . 2008. Converging and wave guiding of Gaussian beam by two-layer dielectric rods. Applied Physics Letters. 93:201101. abstract
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Penciu R S; Aydin K; Kafesaki M; Koschny T; Ozbay E; Economou E N; Soukoulis C M . 2008. Multi-gap individual and coupled split-ring resonator structures. Optics Express. 16:18131-18144. abstract
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Personnel

Postdoctoral Research Associates:

Overview

The goal of this project is the discovery and understanding of new, complex metal-rich solids. The effort brings together two solid-state chemists (Corbett, Miller) and a surface chemist (Thiel) to address fundamentals of designing and perfecting atom- and energy-efficient synthetic methods for new, complex metal-rich materials. These materials provide rich potential for new thermoelectrics, magneto-responsive processes, molecular storage, and coatings. This research team combines expertise in high-temperature synthesis, diffraction and structural analysis, ultra-high vacuum science, electronic structure theory, and surface characterization to study complex bulk and surface structures. The strength of the scientific components is demonstrated by past work on bulk structure and surfaces of quasicrystals, and on bulk Zintl phases. If successful, this project will uncover a wealth of new solid-state phases, and develop general principles for understanding their stability and properties, both bulk and surface.

The highly-interwoven topics in this project are:

  • To discover and design new materials. Our strategy is to combine experiment, viz. exploratory synthesis and temperature-dependent structure determinations, with electronic structure theory to uncover and ultimately design new families of intermetallic phases and to understand the factors that stabilize both new and known phases. In the next three years, for example, we will elucidate precise atomic distributions in complex intermetallic phases, e.g., gamma-brass structures incorporating 3d elements, e.g., Pd-Zn-Al and Mn-Ga-Sn, and quasicrystal approximants, that will establish chemical guidelines for designing new ternary systems, especially those showing quasiperiodicity and potentially interesting itinerant magnetism. We will also investigate how relativistic effects influence and control structure, bonding, and stabilities of intermetallic phases that incorporate 6th period elements, e.g., distinguishing Hg from Tl in BaHg2Tl2 and the new families of gold cluster networks (J. Corbett, G. Miller).
  • To understand surface stability and surface properties of complex metal-rich solids. We will experimentally investigate microscopic and mesoscopic morphology, atomic locations, interfacial growth, friction, and chemical reactivity of Pd-Zn-Al quasicrystals. We will apply the tools developed for the bulk phases, to obtain and understand the surfaces. As an example, theoretical aids for understanding stability, structural features and chemical bonding of complex intermetallic systems will be developed. (P. Thiel, J. Corbett, G. Miller).
  • To establish structure-property relationships. We will establish these for complex metal-rich materials in the bulk and at their surfaces as related to both fundamental as well as practical issues, e.g., thermoelectrics, magnetocalorics, hydrogen storage, tribology, and structural behavior. In the next three years, we will study insertion of interstitial atoms, e.g., hydrogen in La-Al phases, or lattice substitution of selected heteroatoms. (J. Corbett, P. Thiel).

Highlights

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Publications

2008
Unal B; Jenks C J; Thiel P A . 2008. Comparison between experimental surface data and bulk structure models for quasicrystalline AlPdMn: Average atomic densities and chemical compositions. Physical Review B. 77:195419. abstract
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Thiel P A . 2008. Discussion on the surface science of quasicrystals. Philosophical Magazine. 88:2123-2129. abstract
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Postdoctoral Research Associates:

Overview

A major goal of this research is to uncover the underlying electronic, atomic and microscopic interactions that result in an extraordinarily strong coupling between the magnetic and crystal lattices and remarkable responsiveness to both strong (temperature and pressure) and weak (magnetic field) stimuli in some rare earth intermetallic materials. It will be achieved by focusing on the state-of-the-art synthesis, processing and characterization, combined with theory, modeling and computations gauged and refined against reliable experimental data.

The following systems have been selected as model candidates: GdNi and other equiatomic RM compounds (R is a rare earth metal and M is a 3d transition metal or a main Group 14 element), RCo2, La(Fe1‑xSix)13 and hydrides La(Fe1‑xSix)13Hy, and R5T4 compounds (T is a main Group 14 element). These materials exhibit a number of diverse and unique properties associated with magnetic ordering alone, magneto-volume, itinerant electron metamagnetic, and magnetic-martensitic transformations, respectively, which may or may not be driven by a reversible breaking and reforming of specific chemical bonds.

Development and validation of phenomenological models of transformations that range from magneto-volume to magnetic-martensitic is another goal, thus guiding future discoveries of material systems exhibiting strong reactions to small changes of magnetic field, with temperature and pressure providing additional sources of stimulation.

Highlights

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Publications

2008
Xie S; Gschneidner K A; Russell A M . 2008. Microstructure and mechanical properties of the Dy-50(Cu50-xNix) intermetallic B2CsCl-type compounds. Scripta Materialia. 59:810-813. abstract
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Haskel D; Tseng Y C; Souza-Neto N M; Lang J C; Sinogeikin S; Mudryk Y; Gschneidner K A; Pecharsky V K . 2008. Magnetic spectroscopy at high pressures using X-ray magnetic circular dichroism. High Pressure Research. 28:185-192. abstract
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