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Transitions Between Radial And Bipolar Liquid Crystal Drops In The Presence Of Novel Surfactants, Jake Shechter 2020 University of Massachusetts Amherst

Transitions Between Radial And Bipolar Liquid Crystal Drops In The Presence Of Novel Surfactants, Jake Shechter

Doctoral Dissertations

Liquid crystals (LCs) are a class of molecules that form a variety of configurations easily influenced by external interactions. Of particular interest are rod-like LC molecules confined to a spherical geometry, which have a competition between interfacial tension and elastic deformations. The configuration of the liquid crystal inside a droplet can be controlled using surfactants, influencing the boundary conditions, in an oil-in-water emulsion. I tested the effects of novel surfactants on the configuration of the LC droplets. These novel surfactant molecules, synthesized by collaborators, are oligomers with either a variable length hydrophobic domain or protein sensitive hydrophilic domain. I tested ...


Extremely Weakly Interacting Δsz = 0 And Δsz = 1 Excitations And Evidence For Fractional Quantization In A Magnetization Plateau: Cesb, P. G. LaBarre, Brinda Kuthanazhi, C. Abel, Paul C. Canfield, A. P. Ramirez 2020 University of California, Santa Cruz

Extremely Weakly Interacting Δsz = 0 And Δsz = 1 Excitations And Evidence For Fractional Quantization In A Magnetization Plateau: Cesb, P. G. Labarre, Brinda Kuthanazhi, C. Abel, Paul C. Canfield, A. P. Ramirez

Physics and Astronomy Publications

The plateau at 1/3 of the saturation magnetization Ms in the metamagnet CeSb is accompanied by a state of ferromagnetic layers of spins in an up-up-down sequence. We measured M and the specific heat C in the plateau, spin wave analyses of which reveal two distinct branches of excitations. Those with ΔSz=1 as measured by M, coexist with a much larger population of ΔSz=0 excitations measured by C but invisible to M. The large density of ΔSz=0 excitations, their energy gap, and their seeming lack of interaction with ΔSz=1 excitations suggest an analogy with astrophysical ...


Stability Of Group Four Monochalcogenides In Water And Air, William Shattuck 2020 University of Arkansas, Fayetteville

Stability Of Group Four Monochalcogenides In Water And Air, William Shattuck

Theses and Dissertations

Previously published works have simulated the behavior of monolayer group IV monochalcogenides and predicted them to have very useful electronic properties. These simulations have also predicted that monolayers of group IV monochalcogenides will degrade quickly when exposed to water, even in extremely low concentrations. We hypothesize that thin samples of these materials will show signs of degradation if left in air and in water for an extended period of time.

Samples of each of the four monochalcogenides (GeS, GeSe, SnS and SnSe) were exfoliated onto clean oxidized silicon substrates. Chemical analysis showed the SnSe samples were contaminated, so they were ...


Static And Dynamical Properties Of Multiferroics, Sayed Omid Sayedaghaee 2020 University of Arkansas, Fayetteville

Static And Dynamical Properties Of Multiferroics, Sayed Omid Sayedaghaee

Theses and Dissertations

Since the silicon industrial revolution in the 1950s, a lot of effort was dedicated to the research and development activities focused on material and solid-state sciences. As a result, several cutting-edge technologies are emerging including the applications of functional materials in the design and enhancement of novel devices such as sensors, highly capable data storage media, actuators, transducers, and several other types of electronic tools. In the last two decades, a class of functional materials known as multiferroics has captured significant attention because of providing a huge potential for new designs due to possessing multiple ferroic order parameters at the ...


Scaling Law Describes The Spin-Glass Response In Theory, Experiments, And Simulations, Q. Zhai, Deborah L. Schlagel, et al. 2020 University of Texas at Austin

Scaling Law Describes The Spin-Glass Response In Theory, Experiments, And Simulations, Q. Zhai, Deborah L. Schlagel, Et Al.

Ames Laboratory Accepted Manuscripts

The correlation length ξ, a key quantity in glassy dynamics, can now be precisely measured for spin glasses both in experiments and in simulations. However, known analysis methods lead to discrepancies either for large external fields or close to the glass temperature. We solve this problem by introducing a scaling law that takes into account both the magnetic field and the time-dependent spin-glass correlation length. The scaling law is successfully tested against experimental measurements in a CuMn single crystal and against large-scale simulations on the Janus II dedicated computer.


Anisotropic Time-Dependent London Approach: Application To The Ac Response In The Meissner State, Vladimir G. Kogan, Ruslan Prozorov 2020 Ames Laboratory

Anisotropic Time-Dependent London Approach: Application To The Ac Response In The Meissner State, Vladimir G. Kogan, Ruslan Prozorov

Ames Laboratory Accepted Manuscripts

The anisotropic London equations taking into account the normal currents are derived and applied to the problem of the surface impedance in the Meissner state of anisotropic materials. It is shown that the complex susceptibility of the anisotropic slab depends on the orientation of the applied microwave field relative to the crystal axes. In particular, the anisotropic sample in the microwave field is subject to a torque, unless the field is directed along one of the crystal principle axes.


Band Structure Topology And Spin Transport In Magnon Systems, Bo Li 2020 University of Nebraska - Lincoln

Band Structure Topology And Spin Transport In Magnon Systems, Bo Li

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

As the spin excitation quanta in magnetic materials, the magnon is at the heart of the spintronics research because it plays a key role in magnetic dynamics, energy and spin transport, and even determining the ground state of magnetic systems. In this thesis, we will study the band-structure topology and transport properties of magnons in both collinear and noncollinear magnets. Inspired by the great success of topological insulators, exploring magnon topology can unveil the topological nature of bosonic particles and widen the zoo of topological materials. We propose a three-dimensional magnon topological insulator model protected by sublattice chiral symmetries, which ...


Calculations Of Anisotropic Magnetic Properties Using Spin-Orbit Energy Variations, C. Liu, Yongxin Yao, Cai-Zhuang Wang, Kai-Ming Ho, Vladimir P. Antropov 2020 Iowa State University and Ames Laboratory

Calculations Of Anisotropic Magnetic Properties Using Spin-Orbit Energy Variations, C. Liu, Yongxin Yao, Cai-Zhuang Wang, Kai-Ming Ho, Vladimir P. Antropov

Ames Laboratory Accepted Manuscripts

We analyze several methods of obtaining the accurate relativistic total energy (TE) variations using traditional perturbation theories (PTs) and proposed coupling constant integration (CCI) methods. For this purpose, we perform benchmark calculations within the density functional theory taking the spin-orbit coupling (SOC) and its derivative as a perturbation. The TE change due to SOC addition obtained from both PTs and CCI is shown to reach the accuracy of fully self-consistent TE calculations. Similar accuracy is also obtained even for the magnetocrystalline anisotropy energy (MAE). The real advantage of the proposed methods is to use PTs and CCI methods in those ...


Magnetic Detwinning And Biquadratic Magnetic Interaction In Eufe2as2 Revealed By Eu-153 Nmr, Qing-Ping Ding, N. S. Sangeetha, William R. Meier, Mingyu Xu, Sergey L. Bud’ko, Paul C. Canfield, David C. Johnston, Yuji Furukawa 2020 Iowa State University and Ames Laboratory

Magnetic Detwinning And Biquadratic Magnetic Interaction In Eufe2as2 Revealed By Eu-153 Nmr, Qing-Ping Ding, N. S. Sangeetha, William R. Meier, Mingyu Xu, Sergey L. Bud’Ko, Paul C. Canfield, David C. Johnston, Yuji Furukawa

Ames Laboratory Accepted Manuscripts

In the nematic state of iron-based superconductors, twin formation often obscures the intrinsic, anisotropic, in-plane physical properties. Relatively high in-plane external magnetic fields Hext greater than the typical laboratory-scale magnetic fields 10–15 T are usually required to completely detwin a sample. However, recently a very small in-plane Hext∼0.1 T was found to be sufficient for detwinning the nematic domains in EuFe2As2. To explain this behavior, a microscopic theory based on biquadratic magnetic interactions between the Eu and Fe spins has been proposed. Here, using 153Eu nuclear magnetic resonance (NMR) measurements below the Eu2+ ordering temperature, we show ...


First-Order Phase Transition To A Nonmagnetic Ground State In Nonsymmorphic Nbcrp, Yoshiki Kuwata, Hisashi Kotegawa, Hideki Tou, Hisatomo Harima, Qing-Ping Ding, Keiki Takeda, Junichi Hayashi, Eiichi Matsuoka, Hitoshi Sugawara, Takahiro Sakurai, Hitoshi Ohta, Yuji Furukawa 2020 Kobe University and Ames Laboratory

First-Order Phase Transition To A Nonmagnetic Ground State In Nonsymmorphic Nbcrp, Yoshiki Kuwata, Hisashi Kotegawa, Hideki Tou, Hisatomo Harima, Qing-Ping Ding, Keiki Takeda, Junichi Hayashi, Eiichi Matsuoka, Hitoshi Sugawara, Takahiro Sakurai, Hitoshi Ohta, Yuji Furukawa

Ames Laboratory Accepted Manuscripts

We report the discovery of a first-order phase transition at around 125 K in NbCrP, which is a nonsymmorphic crystal with the Pnma space group. From the resistivity, magnetic susceptibility, and nuclear magnetic resonance measurements using crystals made by the Sn-flux method, the high-temperature (HT) phase is characterized to be metallic with a non-negligible magnetic anisotropy. The low-temperature (LT) phase is also found to be a nonmagnetic metallic state with a crystal of lower symmetry. In the LT phase, the spin susceptibility is reduced by ∼30% from that in the HT phase, suggesting that the phase transition is triggered by ...


Dynamic Observation Of Dendritic Quasicrystal Growth Upon Laser-Induced Solid-State Transformation, Insung Han, Joseph T. McKeown, Ling Tang, Cai-Zhuang Wang, Hadi Parsamehr, Zhucong Xi, Ying-Rui Lu, Matthew J. Kramer, Ashwin J. Shahani 2020 University of Michigan

Dynamic Observation Of Dendritic Quasicrystal Growth Upon Laser-Induced Solid-State Transformation, Insung Han, Joseph T. Mckeown, Ling Tang, Cai-Zhuang Wang, Hadi Parsamehr, Zhucong Xi, Ying-Rui Lu, Matthew J. Kramer, Ashwin J. Shahani

Ames Laboratory Accepted Manuscripts

We report the laser-induced solid-state transformation between a periodic “approximant” and quasicrystal in the Al-Cr system during rapid quenching. Dynamic transmission electron microscopy allows us to capture in situ the dendritic growth of the metastable quasicrystals. The formation of dendrites during solid-state transformation is a rare phenomenon, which we attribute to the structural similarity between the two intermetallics. Through ab initio molecular dynamics simulations, we identify the dominant structural motif to be a 13-atom icosahedral cluster transcending the phases of matter.


Using Current-Voltage Characteristics To Probe The Transport Mechanism In Carbon Nanotube Networks, Alejandro Jimenez 2020 California Polytechnic State University, San Luis Obispo

Using Current-Voltage Characteristics To Probe The Transport Mechanism In Carbon Nanotube Networks, Alejandro Jimenez

Physics

Carbon nanotube (CNT) random networks have shown great promise in electronic applications. For example, they have been used as the active layer in thin film transistor biosensors and as electrodes in supercapacitors (Hu, 2010). Although CNT networks applications are numerous, some of the key details of their electrical behavior are not fully understood. In particular, it is known that the junctions between tubes in CNT networks play a key role in determining the sensing properties of the network (Thanihaichelvana, et al., 2018), however, the mechanism by which metallic-semiconducting (m-s) tube junctions affect the electrical sensing properties of the network is ...


Charge Disproportionation In The Spin-Liquid Candidate Κ − (Et)2cu2(Cn)3 At 6 K Revealed By 63cu Nqr Measurements, Takeshi Kobayashi, Qing-Ping Ding, H. Taniguchi, K. Satoh, A. Kawamoto, Yuji Furukawa 2020 Ames Laboratory and Saitama University

Charge Disproportionation In The Spin-Liquid Candidate Κ − (Et)2cu2(Cn)3 At 6 K Revealed By 63cu Nqr Measurements, Takeshi Kobayashi, Qing-Ping Ding, H. Taniguchi, K. Satoh, A. Kawamoto, Yuji Furukawa

Ames Laboratory Accepted Manuscripts

The spin-liquid candidate κ−(ET)2Cu2(CN)3 [ET: bis(ethylenedithio)tetrathiafulvalene] does not exhibit magnetic ordering down to a very low temperature, but shows a mysterious anomaly at 6 K. The origin of the so-called 6-K anomaly is still under debate. We carried out nuclear quadrupole resonance (NQR) measurements on the copper sites of the insulating layers, which are sensitive to the charge dynamics unlike conventional spin-1/2 nuclear magnetic resonance (NMR). The main finding of this Rapid Communication is that the observation of a sharp peak behavior in the nuclear spin-lattice relaxation rate T−11 of 63Cu NQR ...


Spatial Decomposition Of Magnetic Anisotropy In Magnets: Application To Doped Fe16n2, Yang Sun, Yong-Xin Yao, Manh Cuong Nguyen, Cai-Zhuang Wang, Kai-Ming Ho, Vladimir P. Antropov 2020 Columbia University

Spatial Decomposition Of Magnetic Anisotropy In Magnets: Application To Doped Fe16n2, Yang Sun, Yong-Xin Yao, Manh Cuong Nguyen, Cai-Zhuang Wang, Kai-Ming Ho, Vladimir P. Antropov

Ames Laboratory Accepted Manuscripts

We propose a scheme of decomposition of the total relativistic energy in solids to intra- and interatomic contributions. The method is based on a site variation of such fundamental constant as the speed of light. As a practical illustration of the method, we tested such decomposition in the case of a spin-orbit interaction variation for the decomposition of the magnetic anisotropy energy (MAE) in CoPt. We further studied the α′′−Fe16N2 magnet doped by Bi, Sb, Co, and Pt atoms. It was found that the addition of Pt atoms can enhance the MAE by as much as five times while ...


Free-Energy Analysis Of The Nonhysteretic First-Order Phase Transition Of Eu2in, B. P. Alho, P. O. Ribeiro, P. J. von Ranke, F. Guillou, Yaroslav Mudryk, Vitalij K. Pecharsky 2020 Universidade do Estado do Rio de Janeiro - UERJ and Ames Laboratory

Free-Energy Analysis Of The Nonhysteretic First-Order Phase Transition Of Eu2in, B. P. Alho, P. O. Ribeiro, P. J. Von Ranke, F. Guillou, Yaroslav Mudryk, Vitalij K. Pecharsky

Ames Laboratory Accepted Manuscripts

Binary intermetallic Eu2In was recently reported to exhibit a giant anhysteretic magnetocaloric effect due to a first-order magnetic phase transition between paramagnetic and ferromagnetic states. Experimentally, the transition occurs with a small phase volume change, ΔV/V, of approximately 0.1% around TC of ca. 55 K. We represent magnetic and compute magnetocaloric properties of a Eu2In compound using a microscopic description based on a model Hamiltonian that takes into account magnetic exchange and magnetoelastic interactions. In the model the thermodynamic nature of the transition is conveniently represented by a single magnetoelastic interaction parameter. A good agreement between the theoretical ...


Resistivity And Magnetoresistance Properties Of R2nisi3 (R = Gd, Dy, Ho, Er, Tm) Compounds, Santanu Pakhira, R. Ranganathan, Chandan Mazumdar 2020 Iowa State University, Ames Laboratory, and Saha Institute of Nuclear Physics

Resistivity And Magnetoresistance Properties Of R2nisi3 (R = Gd, Dy, Ho, Er, Tm) Compounds, Santanu Pakhira, R. Ranganathan, Chandan Mazumdar

Ames Laboratory Accepted Manuscripts

The resistivity and magnetoresistance behaviour of the hexagonal intermetallic compounds R2NiSi3 (R = Gd, Dy, Ho, Er, and Tm) are reported here. All the studied polycrystalline compounds exhibit metallic behaviour along with additional magnetic anomalies at low temperatures. A well-defined resistivity minima is observed in Gd2NiSi3 and Dy2Ni0.87Si2.95 at a temperature much higher than their respective magnetic transition temperatures. The anomaly has been ascribed to the charge carrier localization caused by magnetic precursor effect. Magnetic field induced crossover from positive to negative magnetoresistance (MR) behaviour associated with antiferromagnetic ground state is evidenced for Gd2NiSi3 and Er2NiSi3 in the low ...


Effect Of Controlled Pointlike Disorder Induced By 2.5-Mev Electron Irradiation On The Nematic Resistivity Anisotropy Of Hole-Doped (Ba,K)Fe2as2, Makariy A. Tanatar, Erik I. Timmons, M. Konczykowski, O. Cavani, Kyuil Cho, Yong Liu, Thomas A. Lograsso, Ruslan Prozorov 2020 Iowa State University and Ames Laboratory

Effect Of Controlled Pointlike Disorder Induced By 2.5-Mev Electron Irradiation On The Nematic Resistivity Anisotropy Of Hole-Doped (Ba,K)Fe2as2, Makariy A. Tanatar, Erik I. Timmons, M. Konczykowski, O. Cavani, Kyuil Cho, Yong Liu, Thomas A. Lograsso, Ruslan Prozorov

Ames Laboratory Accepted Manuscripts

In-plane anisotropy of electrical resistivity was studied in samples of the hole-doped Ba1-xKxFe2As2 in the composition range 0.21 <= x <= 0.26 where anisotropy changes sign. Low-temperature (similar to 20 K) irradiation with relativistic 2.5 MeV electrons was used to control the level of disorder and residual resistivity of the samples. Modification of the stress-detwinning technique enabled measurements of the same samples before and after irradiation, leading to the conclusion of anisotropic character of predominantly inelastic scattering processes. Our main finding is that the resistivity anisotropy is of the same sign irrespective of residual resistivity, and remains the same in the orthorhombic C-2 phase above the reentrant tetragonal transition. Unusual T-linear dependence of the anisotropy Delta rho rho(a) (T ) - rho(b) (T) is found in pristine samples with x = 0.213 and x = 0.219, without similar signatures in either rho(a) (T ) or rho(b) (T ). We show that this feature can be reproduced by a phenomenological model of R. M. Fernandes et al. [Phys. Rev. Lett. 107, 217002 (2011)]. We speculate that onset of fluctuations of nematic order on approaching the instability towards the reentrant tetragonal phase contributes to this unusual dependence.


Stacking Faults And Alternate Crystal Structures For The Shape-Memory Alloy Niti, M. Krcmar, German D. Samolyuk, James R. Morris 2020 Grand Valley State University

Stacking Faults And Alternate Crystal Structures For The Shape-Memory Alloy Niti, M. Krcmar, German D. Samolyuk, James R. Morris

Ames Laboratory Accepted Manuscripts

We use ab initio calculations to study the role of stacking faults in connecting the high-temperature B2 and the theoretically predicted low-temperature B33 NiTi phases. In contrast with prior work, we describe the B2 -> B33 phase transformation in terms of alternate bilayer shifts by 1/2[100] on the (011)(B2) plane, obtaining a viable pathway; the same mechanism could also work with the B19 parent phase. We then examine B33-like structures built from alternate stacking sequences of B19 bilayers, constructed to have monoclinic tilt angles close to the experimentally reported NiTi B19' martensite, and find four low-energy stacking-fault variants ...


Crystal Structure And Physical Properties Of Yb2in And Eu2-Xybxin Alloys, F. Guillou, H. Yibole, R. Hamane, V. Hardy, Y. B. Sun, J. J. Zhao, Yaroslav Mudryk, Vitalij K. Pecharsky 2020 Inner Mongolia Normal University

Crystal Structure And Physical Properties Of Yb2in And Eu2-Xybxin Alloys, F. Guillou, H. Yibole, R. Hamane, V. Hardy, Y. B. Sun, J. J. Zhao, Yaroslav Mudryk, Vitalij K. Pecharsky

Ames Laboratory Accepted Manuscripts

While binary RE2In, where RE = rare earth, have been reported a few decades ago, recent investigations revealed intriguing new physical insights. For instance, the discovery of a nearly ideal first-order ferromagnetic transition in Eu2In calls for further exploration of structures and properties of RE2In, in particular for the least-documented RE = Eu and Yb cases. Here, we investigate Eu2-xYbxIn pseudobinaries with nominal values of x = 0.25, 0.5, 0.75, 1, 1.5, 2 by powder x-ray diffraction (including as function of temperature from 100 to 375 K for Yb2In), magnetization (5-300 K), as well as electrical resistivity (5-300 K ...


Cold Sintering Diisopropylamonium Bromide To Form Organic Ceramic Pellets, Darren Armstrong 2020 University of Nebraska - Lincoln

Cold Sintering Diisopropylamonium Bromide To Form Organic Ceramic Pellets, Darren Armstrong

Honors Theses, University of Nebraska-Lincoln

Diisopropylamonium bromide is an organic ferroelectric compound. Standard sample preparation methods either require a powder or a single crystal. Certain measurements cannot be done on powders due to equipment limitations, and single crystals are difficult and time consuming to produce and handle. Cold sintering is a relatively new process that allows the creation of ceramics. The original cold sintering process was adapted to work for diisopropylamonium bromide. This allows the creation of ceramics with a large surface area. These pellets can achieve up to 95% of the theoretical maximum density. While the pellets are currently unsuitable for electric testing at ...


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