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Vermiculations In Painted Caves: New Inputs From Laboratory Experiments And Field Observations, Perrine Freydier, Eric Weber, Jérôme Martin, Pierre-Yves Jeannin, Béatrice Guerrier, Frédéric Doumenc 2021 Université Paris-Saclay, France

Vermiculations In Painted Caves: New Inputs From Laboratory Experiments And Field Observations, Perrine Freydier, Eric Weber, Jérôme Martin, Pierre-Yves Jeannin, Béatrice Guerrier, Frédéric Doumenc

International Journal of Speleology

Vermiculations are aggregates of small particles commonly found on cave walls. They are a major concern for the conservation of painted caves, as they can potentially alter valuable prehistoric cave paintings. A previous rheological study of fine sediment deposits on cave walls revealed that this material can undergo a solid-to-liquid transition triggered by variations in the chemical composition of the water film on the wall. Such a transition could occur at the origin of vermiculations by allowing the sediment to flow under low mechanical stress. In this work, we provide quantitative information on the conditions leading to this transition and ...


Developing Dynamical Probes Of Quantum Spin Liquids Inspired By Techniques From Spintronics, Joshua Aftergood 2021 The Graduate Center, City University of New York

Developing Dynamical Probes Of Quantum Spin Liquids Inspired By Techniques From Spintronics, Joshua Aftergood

Dissertations, Theses, and Capstone Projects

We theoretically study low dimensional insulating spin systems using spin fluctuations as a probe of the spin dynamics. In some systems, low dimensionality in conjunction with other quantum fluctuation enhancing effects impedes spontaneous generation of long range magnetic ordering down to zero absolute temperature. In particular, we focus on exotic spin systems hosting mobile, fractionalized spin excitations above their ground state, and ultimately show that techniques already commonplace in spintronics can be utilized in the context of quantum magnetism to develop probes of exotic ground states.

We initially consider quantum spin chains (QSCs), and examine a system of two exchange-coupled ...


Nonlinear Optical Studies Of Interfacial Ferroelectricity And Strain Distribution In Perovskite Dielectric Films, Tony Le 2021 The Graduate Center, City University of New York

Nonlinear Optical Studies Of Interfacial Ferroelectricity And Strain Distribution In Perovskite Dielectric Films, Tony Le

Dissertations, Theses, and Capstone Projects

Dielectric and ferroelectric perovskite films have been model energy storage structures for their low-dielectric loss, extremely high charge-discharge speed, and good temperature stability, yet there is still much to understand about the material’s limitations. This dissertation presents a detailed understanding of the strain-induced ferroelectricity at the boundary between a strontium titanate (SrTiO3) ultrathin film epitaxially grown on a germanium (Ge) substrate through optical second harmonic generation (SHG), and the polydomain distribution in the Zr-doped BaTiO3 (BZT) films by time-resolved pump-probe spectroscopy.

First, SHG measurements were performed to reveal interfacial ferroelectricity in the epitaxial SrTiO3/Ge (100 ...


Wave Excitation And Dynamics In Disordered Systems, Yiming Huang 2021 The Graduate Center, City University of New York

Wave Excitation And Dynamics In Disordered Systems, Yiming Huang

Dissertations, Theses, and Capstone Projects

This thesis presents studies of the field and energy excited in disordered systems as well as the dynamics of scattering.

Dynamic and steady state aspects of wave propagation are deeply connected in lossless open systems in which the scattering matrix is unitary. There is then an equivalence among the energy excited within the medium through all channels, the Wigner time delay, which is the sum of dwell times in all channels coupled to the medium, and the density of states. But these equivalences fall away in the presence of material loss or gain. In this paper, we use microwave measurements ...


Physical Properties Of Polar Magnetic Oxides Hofewo6, 2021 Kennesaw State University

Physical Properties Of Polar Magnetic Oxides Hofewo6

Symposium of Student Scholars

Polar magnetic oxides are interesting systems to study due to the possibility of hosting functional properties such as ferroelectricity, piezoelectricity, etc. In this work, a new compound HoFeWO6 is synthesized using high-temperature solid-state reaction and characterized using x-ray diffraction, neutron diffraction, magnetization measurements, and dielectric measurements. The x-ray and neutron diffraction results indicate that HoFeWO6 crystallizes in polar (non-centrosymmetric and achiral) orthorhombic structure P n a 21. The magnetization measurements indicate that HoFeWO6 exhibit paramagnetic to antiferromagnetic transition at TN = 18 K. The dielectric properties at room temperature indicate that the dielectric constant decreases with an ...


Symphas: A Modular Api For Phase-Field Modeling Using Compile-Time Symbolic Algebra, Steven A. Silber 2021 The University of Western Ontario

Symphas: A Modular Api For Phase-Field Modeling Using Compile-Time Symbolic Algebra, Steven A. Silber

Electronic Thesis and Dissertation Repository

The phase-field method is a common approach to qualitative analysis of phase transitions. It allows visualizing the time evolution of a phase transition, providing valuable insight into the underlying microstructure and the dynamical processes that take place. Although the approach is applied in a diverse range of fields, from metal-forming to cardiac modelling, there are a limited number of software tools available that allow simulating any phase-field problem and that are highly accessible. To address this, a new open source API and software package called SymPhas is developed for simulating phase-field and phase-field crystal in 1-, 2- and 3-dimensions. Phase-field ...


Heat Flow In The Core Of Ganymede: High Pressure-Temperature Electrical Resistivity Measurements Of Solid And Liquid Ag And Fe-S Alloys, Joshua A.H. Littleton 2021 The University of Western Ontario

Heat Flow In The Core Of Ganymede: High Pressure-Temperature Electrical Resistivity Measurements Of Solid And Liquid Ag And Fe-S Alloys, Joshua A.H. Littleton

Electronic Thesis and Dissertation Repository

Experimental investigations of materials at high pressures (P) and temperatures (T) provide insight into the properties and behaviours expected within the inaccessible interiors of planetary bodies. Using a four-wire electrical resistance technique, the electrical resistivity (ρ) of 4d transition metal (Ag) and 3d transition metal alloys (Fe-S) were measured in the solid and molten states at high P. The thermal conductivity (κ) of these materials is inversely proportional to ρ, as described by the Wiedemann-Franz Law. When applied to planetary cores, κ is an important parameter that regulates heat transport mechanisms and magnetic field production.

A hypothesis of ‘resistivity invariance ...


Manipulation Of Spin Crossover Phenomenon In An Fe (Ii) Molecular Complex And Application To Molecular Spintronics, Guanhua Hao 2021 University of Nebraska - Lincoln

Manipulation Of Spin Crossover Phenomenon In An Fe (Ii) Molecular Complex And Application To Molecular Spintronics, Guanhua Hao

Theses, Dissertations, and Student Research: Department of Physics and Astronomy

Molecules with a large local magnetic moment have attracted considerable attention for application in spintronic devices. One candidate of a suitable device goes to the spin crossover molecule, where these 3d transition metal compounds are able to exhibit a robust spin state transition between distinct states. By proper design, the spintronic devices fabricated via spin crossover molecular thin films could achieve novel functionality while retaining flexibility and other traits based on its “organic” nature.

Controlling the spin state transition is a key factor of these possibilities. This thesis work investigates the manipulation of the spin state transition in [Fe ...


Voltage-Controlled Magnetization In Chromia-Based Magnetic Heterostructures, William Echtenkamp 2021 University of Nebraska-Lincoln

Voltage-Controlled Magnetization In Chromia-Based Magnetic Heterostructures, William Echtenkamp

Theses, Dissertations, and Student Research: Department of Physics and Astronomy

Spintronics promises a new generation of low-power, high-speed, non-volatile memory and logic devices. Heterostructures based on magnetoelectric chromia enable the direct manipulation of magnetization by applied electric fields and emerged as a promising building block for spintronic devices. In this dissertation, several interesting emergent magnetic properties arising in these device-enabling building blocks are examined. In some cases, exchange coupling at the interface between the magnetoelectric antiferromagnet and an adjacent ferromagnet stabilizes the interfacial antiferromagnetic domain state against the electrically induced rotation of the bulk spin structure. Upon magnetically cycling the ferromagnet, the magnetoelectric antiferromagnet relaxes towards a commensurate spin structure ...


Computational Studies Of Carbon Nanocluster Solidification, Chathuri C. Silva 2021 University of Missouri-St. Louis

Computational Studies Of Carbon Nanocluster Solidification, Chathuri C. Silva

Dissertations

A subset of micron-size meteoritic carbon particles formed in red giant atmospheres show a core-rim structure, likely condensed from a vapor phase into super-cooled carbon droplets that nucleated graphene sheets (~40Å) on randomly oriented 5-atom loops during solidification, followed by coating with a graphite rim. Similar particles form during slow cooling of carbon vapor in the lab.

Here we investigate the nucleation and growth of carbon rings and graphene sheets using density functional theory (DFT). Our objectives: (1). explore different computational techniques in DFT-VASP for various carbon structures and compare the results with literature, (2). investigate the nucleation and growth ...


Campbell Penetration Depth In Low Carrier Density Superconductor Yptbi, Hyunsoo Kim, Makariy A. Tanatar, Halyna Hodovanets, Kefeng Wang, Johnpierre Paglione, Ruslan Prozorov 2021 Ames Laboratory, Iowa State University, University of Maryland, and Texas Tech University

Campbell Penetration Depth In Low Carrier Density Superconductor Yptbi, Hyunsoo Kim, Makariy A. Tanatar, Halyna Hodovanets, Kefeng Wang, Johnpierre Paglione, Ruslan Prozorov

Ames Laboratory Accepted Manuscripts

Magnetic penetration depth, λm, was measured as a function of temperature and magnetic field in single crystals of low carrier density superconductor YPtBi by using a tunnel-diode oscillator technique. Measurements in zero DC magnetic field yield London penetration depth, λL(T), but in the applied field the signal includes the Campbell penetration depth, λC(T), which is the characteristic length of the attenuation of small excitation field, HAC, into the Abrikosov vortex lattice due to its elasticity. Whereas the magnetic field dependent λC exhibit λC∼Bp with p=1/2 in most of the conventional and unconventional superconductors, we found ...


Numerical Calculation Of Losses Of Trapped Vortices Under Strong Rf Meissner Current And Dc Superheating Field In Type Ii Superconductors, Walive Pathiranage Manula Randhika Pathirana 2021 Old Dominion University

Numerical Calculation Of Losses Of Trapped Vortices Under Strong Rf Meissner Current And Dc Superheating Field In Type Ii Superconductors, Walive Pathiranage Manula Randhika Pathirana

Physics Theses & Dissertations

Research on the vortex dynamics and enhancing of superheating field in superconductors has attracted much attention in accelerator physics community to develop next-generation high-performance accelerator cavities. However, the extreme dynamics of curvilinear elastic vortices driven by very strong currents close to the depairing limit or superheating field of a superconductor with a nanostructured surface has not been well understood. We calculated the superheating field Hsh and critical momentum kc characterizing the wavelength of the instability λm of the Meissner state to flux penetration by solving numerically the Ginzburg-Landau equations. A bulk superconductor, superconductor with the inhomogeneous surface disorder ...


Population Annealing: Analysis, Optimization And Application To Glassy Systems, Christopher A. Amey 2021 University of Massachusetts Amherst

Population Annealing: Analysis, Optimization And Application To Glassy Systems, Christopher A. Amey

Doctoral Dissertations

Glasses are physical systems that lack structural order and exhibit extremely slow dynamics, which makes them challenging to study. In this thesis we apply Monte Carlo methods to two distinct glassy systems: the 3D Edwards-Anderson spin glass and a binary hard sphere fluid. While significant progress has been made on theoretical and experimental fronts, much of our current understanding of glasses has come from numerical simulations. Standard Monte Carlo techniques cannot be used to perform equilibrium simulations due to slow dynamics in the glassy regime. As a result, several specialized techniques have been developed in order to simulate such systems ...


Quasi-One-Dimensional Uniform Spin-1/2 Heisenberg Antiferromagnet Knacup2o7 Probed By P-31 And Na-23 Nmr, S. Guchhait, Qing-Ping Ding, M. Sahoo, A. Giri, S. Maji, Yuji Furukawa, R. Nath 2021 Indian Institute of Science Education and Research

Quasi-One-Dimensional Uniform Spin-1/2 Heisenberg Antiferromagnet Knacup2o7 Probed By P-31 And Na-23 Nmr, S. Guchhait, Qing-Ping Ding, M. Sahoo, A. Giri, S. Maji, Yuji Furukawa, R. Nath

Ames Laboratory Accepted Manuscripts

We present the structural and magnetic properties of KNaCuP2O7 investigated via x-ray diffraction, magnetization, specific heat, and (31)p and Na-23 NMR measurements and complementary electronic structure calculations. The temperature-dependent magnetic susceptibility and P-31 NMR shift could be modeled very well by the uniform spin-1/2 Heisenberg antiferromagnetic chain model with a nearest-neighbor interaction J/k(B) similar or equal to 58.7 K. The corresponding mapping using first-principles electronic structure calculations leads to J(DFT)/k(B) similar or equal to 59 K with negligibly small interchain couplings, further confirming that the system is indeed a one-dimensional uniform spin-1 ...


Metamagnetism Of Few-Layer Topological Antiferromagnets, C. Lei, O. Heinonen, A. H. MacDonald, Robert J. McQueeney 2021 University of Texas at Austin

Metamagnetism Of Few-Layer Topological Antiferromagnets, C. Lei, O. Heinonen, A. H. Macdonald, Robert J. Mcqueeney

Ames Laboratory Accepted Manuscripts

MnBi2Te4 (MBT) materials are a promising class of antiferromagnetic topological insulators whose films provide access to novel and technologically important topological phases, including quantum anomalous Hall states and axion insulators. MBT device behavior is expected to be sensitive to the various collinear and noncollinear magnetic phases that are accessible in applied magnetic fields. Here, we use classical Monte Carlo simulations and electronic structure models to calculate the ground state magnetic phase diagram as well as topological and optical properties for few-layer films with up to six septuple layers. Using magnetic interaction parameters appropriate for MBT, we find that it is ...


Magnetic Order In The Van Der Waals Antiferromagnet Crps4: Anisotropic H-T Phase Diagrams And Effects Of Pressure, Sergey L. Bud’ko, Elena Gati, Tyler J. Slade, Paul C. Canfield 2021 Iowa State University and Ames Laboratory

Magnetic Order In The Van Der Waals Antiferromagnet Crps4: Anisotropic H-T Phase Diagrams And Effects Of Pressure, Sergey L. Bud’Ko, Elena Gati, Tyler J. Slade, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

Single crystalline samples of the van der Waals antiferromagnet CrPS4 were studied by measurements of specific heat and comprehensive anisotropic temperature- and magnetic-field-dependent magnetization. In addition, measurements of the heat capacity and magnetization were performed under pressures of up to ∼21 and ∼14 kbar, respectively. At ambient pressure, two magnetic transitions are observed: second order from a paramagnetic to an antiferromagnetic state at TN∼37 K, and a first-order spin reorientation transition at T∗∼34 K. Anisotropic H−T phase diagrams were constructed using the M(T,H) data. As pressure is increased, TN is weakly suppressed with dTN/dP ...


Novel Low Temperature Properties Of Filled And Unfilled Single Crystal Irsb3, Matthew Cook 2021 Western Michigan University

Novel Low Temperature Properties Of Filled And Unfilled Single Crystal Irsb3, Matthew Cook

Dissertations

The skutterudite family of materials has garnered a lot of attention in the condensed matter community and it persists to be an important system for exploring the fundamental physics of solids. The initial interest into compounds with this common structure was due to their promising thermoelectric properties giving the possibility of efficient energy harvesting. Since, there has been a huge effort to systematically synthesize new filled skutterudite compounds, as nearly every type of strongly correlated behavior has been found within this family. As the field of topological materials has gained momentum, these materials have also been given a renewed interest ...


Skyrmions And Biskyrmions In Magnetic Films, Daniel Capic 2021 The Graduate Center, City University of New York

Skyrmions And Biskyrmions In Magnetic Films, Daniel Capic

Dissertations, Theses, and Capstone Projects

Skyrmions have garnered significant attention in condensed matter systems in recent years. In principle, they are topologically protected, so there is a large energy barrier preventing their annihilation. Furthermore, they can exist at the nanoscale, be manipulated with very small currents, and be created by a number of different methods. This makes them attractive for use in potential computing applications. This work studies ferromagnetic skyrmions. In particular, it highlights our small contributions to the field of skyrmions in condensed matter systems, specifically in thin-film ferromagnets.


Optimization Of Materials For Magnetic Refrigeration And Thermomagnetic Power Generation, Anthony N. Tantillo 2021 The Graduate Center, City University of New York

Optimization Of Materials For Magnetic Refrigeration And Thermomagnetic Power Generation, Anthony N. Tantillo

Dissertations, Theses, and Capstone Projects

The magnetocaloric effect, by which a magnetic material experiences a change in temperature due to an applied magnetic field, can be used for refrigeration. The corollary to the magnetocaloric effect -- known as the pyromagnetic effect -- is the phenomenon by which a magnetic material experiences a thermally-induced change in magnetization that can be used to harvest thermal energy. This dissertation has two main parts: one focusing on novel materials for energy harvesting; and another focusing on methods of materials discovery for refrigeration purposes. Thermomagnetic power generation (TMG) is the process by which magnetic flux, which comes from a temperature-driven change of ...


Quantum Transport In Topological Magnets, Haiming Deng 2021 The Graduate Center, City University of New York

Quantum Transport In Topological Magnets, Haiming Deng

Dissertations, Theses, and Capstone Projects

In the past several years, a new field of symmetry-protected topological materials has emerged in condensed matter physics, based on the wide range of consequences that result from the realization that certain properties of physical systems can be expressed as topological invariants, which are insensitive to local perturbations. This new class of materials hosts unique surface/edge states, such as the first known topological system – quantum Hall insulator with dissipationless chiral edge states, and massless spin-helical Dirac surface states in 3D topological insulators that are unlike any other known 1D or 2D electronic systems. In this thesis, to understand the ...


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