Condensed Matter Physics Commons^™

Electrical And Magnetic Transport Properties Of Periodic And Aperiodic Artificial Spin Ice Systems, Justin Woods

Theses and Dissertations--Physics and Astronomy

In recent years, the topic of magnetic frustration in systems and the effect that frustration can have on system dynamics has been a rich environment for study. One such system that lends itself directly to this study are systems of single domain ferromagnetic bars in two dimensions. These ferromagnetic bars can be fabricated from a thin film using current lithography techniques. The bars are fabricated in such a way that their shape anisotropy dictates the magnetization of the bar will be a single domain, Ising-like magnetic moment. These single domain magnetic bars scan be arranged to introduce frustration of their …

A Theoretical And Experimental Study Of Charge Transport In Organic Thermoelectric Materials And Charge Transfer States In Organic Photovoltaics, Ashkan Abtahi

Theses and Dissertations--Physics and Astronomy

Applications of organic electronics have increased significantly over the past two decades. Organic semiconductors (OSC) can be used in mechanically flexible devices with potentially lower cost of fabrication than their inorganic counterparts, yet in many cases organic semiconductor-based devices suffer from lower performance and stability. Investigating the doping mechanism, charge transport, and charge transfer in such materials will allow us to address the parameters that limit performance and potentially resolve them. In this dissertation, organic materials are used in three different device structures to investigate charge transport and charge transfer. Chemically doped π-conjugated polymers are promising materials to be used …

Effects Of Aperiodicity And Frustration On The Magnetic Properties Of Artificial Quasicrystals, Barry Farmer

Theses and Dissertations--Physics and Astronomy

Quasicrystals have been shown to exhibit physical properties that are dramatically different from their periodic counterparts. A limited number of magnetic quasicrystals have been fabricated and measured, and they do not exhibit long-range magnetic order, which is in direct conflict with simulations that indicate such a state should be accessible. This dissertation adopts a metamaterials approach in which artificial quasicrystals are fabricated and studied with the specific goal of identifying how aperiodicity affects magnetic long-range order. Electron beam lithography techniques were used to pattern magnetic thin films into two types of aperiodic tilings, the Penrose P2, and Ammann-Beenker tilings. SQUID …

Synthesis And Characterization Of Hybrid Organic Coating System To Reduce Thermal Degradation Of Solar Cells, Mohd Zaini Farah Khaleda

Student Works (2020-2029)

Thermal-decreasing hybrid organic coatings were developed for crystalline solar cells by using two types of binder systems; namely Aminopropyltriethoxysolution (APTES) / Methyltrimethoxysilane (MTMS) binder system (labelled as B1) and Methyltrimethoxysilane (MTMS) / nitric acid (HNO3) binder system (labelled as B2). Three types of nanoparticles; Titanium dioxide, TiO2 (Anatase), Zinc oxide, ZnO and Tin dioxide, SnO2 nanoparticles with different weight percentage were introduced inside each binder system namely; 20 wt%, TiO2 (T1B1 coating), 60 wt% TiO2 (T2B1 coating), 20 wt% ZnO (Z1B1 coating), 60 wt% ZnO (T2B1 coating), 20 wt% SnO2 (S1B1 coating) and 60 wt% SnO2 (S2B1 coating) for B1 …

Characterization Of Reduced Graphene Oxide Anode For Application In Algae Biophotovoltaic Platforms, Siti Aisyah Ibrahim

Student Works (2020-2029)

Research interest in recent times has placed much focus on electrode technology for biophotovoltaics (BPV) especially in algal fuel cells (AFCs) application. The purpose of this investigation is therefore directed towards optimizing reduced graphene oxide (rGO) thin film as an electrode for AFCs application by means of annealing and plasma treatment. First stage involves deposition of six (6) layers of rGO thin film using Langmuir-Blodgett (LB) method. The anode electrodes were then annealed at different temperatures under vacuum condition. For plasma treatment meanwhile, a variation of voltage was used to vary the plasma conditions resulting in different surface morphology. To …

Controlling Spin Current Polarization Through Non-Collinear Antiferromagnetism, T. Nan, Camilo X. Quintela, J. Irwin, Gautam Gurung, D. F. Shao, J. Gibbons, Neil Campbell, K. Song, Si-Young Choi, L. Guo, R. D. Johnson, P. Manuel, R. V. Chopdekar, I. Hallsteinsen, Thomas Tybell, P. J. Ryan, J.-W. Kim, Y. Choi, P. G. Radaelli, D. C. Ralph, Evgeny Y. Tsymbal, M. S. Rzchowski, Chang-Beom Eom

Evgeny Tsymbal Publications

The interconversion of charge and spin currents via spin-Hall effect is essential for spintronics. Energy-efficient and deterministic switching of magnetization can be achieved when spin polarizations of these spin currents are collinear with the magnetization. However, symmetry conditions generally restrict spin polarizations to be orthogonal to both the charge and spin flows. Spin polarizations can deviate from such direction in nonmagnetic materials only when the crystalline symmetry is reduced. Here, we show control of the spin polarization direction by using a non-collinear antiferromagnet Mn₃GaN, in which the triangular spin structure creates a low magnetic symmetry while maintaining a …

Insulator-To-Conductor Transition Controlled By The Rashba-Zeeman Effect, Lingling Tao, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

The Rashba effect has recently attracted great attention owing to emerging physical properties associated with it. The interplay between the Rashba effect and the Zeeman effect, being produced by the exchange field, is expected to broaden the range of these properties and even result in novel phenomena. Here we predict an insulator-to-conductor transition driven by the Rashba–Zeeman effect. We first illustrate this effect using a general Hamiltonian model and show that the insulator-to-conductor transition can be triggered under certain Rashba and exchange-field strengths. Then, we exemplify this phenomenon by considering an Ag₂Te/Cr₂O₃ heterostructure, where the …

Nonlinear Anomalous Hall Effect For Néel Vector Detection, Ding-Fu Shao, Shu-Hui Zhang, Gautam Gurung, Wen Yang, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Antiferromagnetic (AFM) spintronics exploits the N´eel vector as a state variable for novel spintronic devices. Recent studies have shown that the fieldlike and antidamping spin-orbit torques (SOTs) can be used to switch the N´eel vector in antiferromagnets with proper symmetries. However, the precise detection of the N´eel vector remains a challenging problem. In this Letter, we predict that the nonlinear anomalous Hall effect (AHE) can be used to detect the N´eel vector in most compensated antiferromagnets supporting the antidamping SOT. We show that the magnetic crystal group symmetry of these antiferromagnets combined with spin-orbit coupling produce a sizable Berry curvature …

Interfacial Contributions To Spin-Orbit Torque And Magnetoresistance In Ferromagnet/Heavy-Metal Bilayers, Kirill Belashchenko, Alexey Kovalev, Mark Van Schilfgaarde

Department of Physics and Astronomy: Faculty Publications

The thickness dependence of spin-orbit torque and magnetoresistance in ferromagnet/heavy-metal bilayers is studied using the first-principles nonequilibrium Green’s function formalism combined with the Anderson disorder model. A systematic expansion in orthogonal vector spherical harmonics is used for the angular dependence of the torque. The dampinglike torque in Co/Pt and Co/Au bilayers can be described as a sum of the spin-Hall contribution, which increases with thickness in agreement with the spin-diffusion model, and a comparable interfacial contribution. The magnetoconductance in the plane perpendicular to the current in Co/Pt bilayers is of the order of a conductance quantum per interfacial atom, exceeding …

Magnonic Analog Of The Edelstein Effect In Antiferromagnetic Insulators, Bo Li, Alexander Mook, Aldo Raeliarijaona, Alexey Kovalev

Department of Physics and Astronomy: Faculty Publications

We investigate the nonequilibrium spin polarization due to a temperature gradient in antiferromagnetic insulators, which is the magnonic analog of the inverse spin-galvanic effect of electrons. We derive a linear-response theory of a temperature-gradient-induced spin polarization for collinear and noncollinear antiferromagnets, which comprises both extrinsic and intrinsic contributions. We apply our theory to several noncentrosymmetric antiferromagnetic insulators, i.e., to a one-dimensional antiferromagnetic spin chain, a single layer of kagome noncollinear antiferromagnet,e.g.,KFe3(OH)6(SO4)2,and a noncollinear breathing pyrochlore antiferromagnet, e.g., LiGaCr4O8. The shapes of our numerically evaluated response tensors agree with those implied by the magnetic symmetry. Assuming a realistic temperature gradient of …

Magnon Landau Levels And Spin Responses In Antiferromagnets, Bo Li, Alexey Kovalev

Department of Physics and Astronomy: Faculty Publications

We study gauge fields produced by gradients of the Dzyaloshinskii-Moriya interaction and propose a model of an AFM topological insulator of magnons. In the long wavelength limit, the Landau levels induced by the inhomogeneous Dzyaloshinskii-Moriya interaction exhibit relativistic physics described by the Klein-Gordon equation. The spin Nernst response due to the formation of magnonic Landau levels is compared to similar topological responses in skyrmion and vortex-antivortex crystal phases of AFM insulators. Our studies show that AFM insulators exhibit rich physics associated with topological magnon excitations.

Ferroelectric Domain Wall Memristor, James P. V. Mcconville, Haidong Lu, Bo Wang, Yueze Tan, Charlotte Cochard, Michele Conroy, Kalani Moore, Alan Harvey, Ursel Bangert, Long-Qing Chen, Alexei Gruverman, J. M. Gregg

Alexei Gruverman Publications

A domain wall-enabled memristor is created, in thin film lithium niobate capacitors, which shows up to twelve orders of magnitude variation in resistance. Such dramatic changes are caused by the injection of strongly inclined conducting ferroelectric domain walls, which provide conduits for current flow between electrodes. Varying the magnitude of the applied electric-field pulse, used to induce switching, alters the extent to which polarization reversal occurs; this systematically changes the density of the injected conducting domain walls in the ferroelectric layer and hence the resistivity of the capacitor structure as a whole. Hundreds of distinct conductance states can be produced, …

Quantitative Study Of The Energy Changes In Voltage-Controlled Spin Crossover Molecular Thin Films, Aaron Mosey, Ashley S. Dale, Guanhua Hao, Alpha T. N’Diaye, Peter Dowben, Ruihua Cheng

Peter Dowben Publications

Voltage-controlled nonvolatile isothermal spin state switching of a [Fe{H2B(pz)₂}₂(bipy)] (pz=tris(pyrazol-1-1y)-borohydride, bipy=2,2’-bipyridine) film, more than 40 to 50 molecular layers thick, is possible when it is adsorbed onto a molecular ferroelectric substrate. Accompanying this high spin and low spin state switching, at room temperature, we observe a remarkable change in conductance, thereby allowing not only non-volatile voltage control of the spin state (“write”), but also current sensing of the molecular spin state (“read”). Monte Carlo Ising model simulations of the high spin state occupancy, extracted from x-ray absorption spectroscopy, indicate that the energy difference between the low …

Growth And Characterization Of Organic Ferroelectric And Magnetic Thin Films, Xuanyuan Jiang

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

Compared to inorganic materials, organic materials are environmentally friendly, flexible, and often with low cost. Inspired by these advantages, organic materials-based electronics have been intensively studied for comparable or better functionalities to inorganic electronics.

This dissertation mainly focuses on the growth and characterizations of organic ferroelectrics and magnetic thin films. For organic ferroelectrics, we investigate the growth and ferroelectric measurements of thin film croconic acid (CA), a proton-transfer molecular ferroelectric (FE) material with a large spontaneous polarization and a small coercive field, as well as the origin of ferroelectricity in CA in terms of the photostriction effect, including the discovery …

Study Of Amorphous Boron Carbide And Hydrogenated Boron Carbide Materials Using Molecular Dynamics And Hybrid Reverse Monte Carlo, Rajan Khadka

Graduate Theses/Dissertations

We present a computational study of amorphous boron carbide (a-B_xC) models using Molecular Dynamics (MD) studied with Stillinger-Weber (SW) and ReaxFF potential. The atomic structure factor (S(Q)), radial distribution function (RDF) and bond lengths comparison with other experimental and ab initio models shows that a random arrangement of icosahedra (B₁₂, B₁₁C) interconnected by chains (CCC, CBC) are present in a-B_xC. Afterward, Hybrid Reverse Monte Carlo (HRMC) technique is used to recreate a-B_xC structures. The existing SW potential parameters of Boron are optimized for the α-rhombohedral (Icosahedral B_{12 …}

Theoretical Investigations Of The Electronic, Magnetic, And Thermoelectric Properties Of Transition-Metal Based Compounds, Haleoot Edaan Raad

Graduate Theses and Dissertations

The electronic, magnetic, and thermoelectric properties of transition-metal based compounds were investigated by using the density functional theory and Boltzmann transport formalism. It was found that the Co-based Heusler compounds and InSe monochalcogenide are among the materials that may be used for future thermoelectric devices. Furthermore, the investigation showed that the quaternary Heusler compounds, such as, CoFeYGe, where Y is Ti or Cr, are half-metallic ferromagnetic materials with full electron spin polarization. The lattice thermal conductivity (κL) was found to decrease for these alloys as the temperature increases. The present investigation indicated that the phonon optical modes have a major …

Studies Of Initial Growth Of Gan On Inn, Alaa Alnami

Graduate Theses and Dissertations

III-nitride materials have recently attracted much attention for applications in both the microelectronics and optoelectronics. For optoelectronic devices, III-nitride materials with tunable energy band gaps can be used as the active region of devices to enhance the absorption or emission. A such material is indium nitride (InN), which along with gallium nitride (GaN) and aluminum nitride (AlN) embody the very real promise of forming the basis of a broad spectrum, a high efficiency solar cell. One of the remaining complications in incorporating InN into a solar cell design is the effects of the high temperature growth of the GaN crystal …

Transport Signatures Of Dirac States In Topological Insulator - Ferromagnet Heterostructures, Hilary M. Hurst

Faculty Research, Scholarly, and Creative Activity

No abstract provided.

First-Principles Simulations Of Materials Under Extreme Conditions, Kien Nguyen Cong

USF Tampa Graduate Theses and Dissertations

The investigation of materials at extreme conditions of high pressure and temperature (high-PT), has been one of the greatest scientific endeavors in condensed mater physics, chemistry, astronomy, planetary, and material sciences. Being subjected to high-PT conditions, materials exhibit dramatic changes in both atomic and electronic structure resulting in an emergence of exceptionally interesting phenomena including structural and electronic phase transitions, chemical reactions, and formation of novel compounds with never-previously observed physical and chemical properties. Although new exciting experimental developments in static and dynamic compression combined with new diagnostics/characterization methods allow to uncover new processes and phenomena at high P-T conditions, …

Why The Crackling Deformations Of Single Crystals, Metallic Glasses, Rock, Granular Materials, And The Earth’S Crust Are So Surprisingly Similar, Karin A. Dahmen, Jonathan T. Uhl, Wendelin J. Wright

Faculty Journal Articles

Recent experiments show that the deformation properties of a wide range of solid materials are surprisingly similar. When slowly pushed, they deform via intermittent slips, similar to earthquakes. The statistics of these slips agree across vastly different structures and scales. A simple analytical model explains why this is the case. The model also predicts which statistical quantities are independent of the microscopic details (i.e., they are "universal"), and which ones are not. The model provides physical intuition for the deformation mechanism and new ways to organize experimental data. It also shows how to transfer results from one scale to another. …