Physical Sciences and Mathematics Commons^™

Diffuse Scattering And 3d-∆Pdf Analyses: Order-Disorder Phase Transitions In (Sr1−Xcax)3rh4sn13 And Nano2, Puspa Upreti

Graduate Research Theses & Dissertations

Classification of structural phase transitions as being of the displacive or order-disorder types is usually done based on spectroscopic measurements performed above the transition. Transitions of the displacive type typically occur when soft phonon modes condense upon approaching the phase transition, whereas those of the order-disorder type are characterized by structures in which the atoms are located randomly above the phase transition at T* at the minima of a multiwell potential. In the ordered state, i.e., when T

We have performed single crystal x-ray scattering experiments and three-dimensional pair distribution functions (3D-∆PDF) analyses to understand the nature of phase transitions …

Magnetic Charge Ordering Of Pinwheel Artificial Spin Ice In In-Plane External Magnetic Fields And Its Application For Tunable Vortex Pinning, Timothy Draher

Graduate Research Theses & Dissertations

Pinwheel artificial spin ice (ASI) systems fabricated using permalloy nanobars offer tunable control of superconducting vortices in an ASI-superconductor hybrid. Vortex pinningis achieved by tuning the ordering of the ASI’s magnetic charge distribution via an external field to create an optimal potential energy landscape to which superconducting vortex motion can be impeded or pinned. Magnetic charge ordering in a pinwheel ASI is visualized using MuMax3 micromagnetic simulations to aid in characterizing the correlation of charge ordering amongst the spin ice system with the application of the external field. Vortex pinning is characterized in a sample of pinwheel spin ice patterned …

Experimental Exploration Of Shared Magnetic Phases Between Diverse Systems Of Iron-Pnictide Superconductors, Ryan Scott Stadel

Graduate Research Theses & Dissertations

The exciting field of iron-pnictide superconductors offers unique opportunities for studying the relationship between magnetism and unconventional superconductivity. This is vital to developing an understanding of the microscopic origin of high-temperature superconductivity, which is itself an important step in harnessing such a potentially revolutionary technology.

Polycrystalline and crystalline samples are synthesized over a diverse collection of related iron-pnictide systems including (Ca,Sr,Ba)1-xNaxFe2As2, Ba(Fe1-xCox)2As2 (122s), and LaFeAs1-xPxO, and TbFeAs1-xPxO (1111s). These compounds are characterized through various types of neutron and x-ray diffraction on multiple instruments, as well as muon spin resonance, and magnetic susceptibility measurements.

A thorough investigation into the conditions under …

Superconducting Cuprates: Synthesis, Characterization And Diffuse Scattering Properties, Bisham Poudel

Graduate Research Theses & Dissertations

Since its discovery more than a century ago, the fascinating phenomenon of superconductivity remains as mysterious as ever with the greatest challenge facing the condensed matter community being the elusive understanding of the microscopic origin leading to its inception. Many outstanding questions remain of which the role played by nematic fluctuations and structural disorder for the stabilization of superconductivity is not well understood. In this respect, superconducting YBa2Cu3O6+x (YBCO)-type cuprates present an ideal framework in which charge doping, structural disorder and various site manipulations can be explored in efforts to address some of these questions. Extensive synthesis and characterization efforts …

The Synthesis Of Pb2sr2sm1-Xcaxcu3o8 And Characterization Of Its Structural And Superconducting Properties., Deblina Das

Graduate Research Theses & Dissertations

Superconducting lead-based cuprate materials of the 2213 structural type, Pb2Sr2MCu3O8 (M=Sm1-xCax, Y1-xCax, Er1-xCax and Yb1-xCax), were synthesized and characterized using x-ray powder diffraction and the Rietveld structural refinements method. Pb2Sr2Sm1-xCaxCu3O8 single crystals were grown by an optimized flux method using various combinations of PbO/PbF2 solvents. Samples with different Sm/Ca ratios were investigated for their superconducting properties. Magnetic measurements reveal the presence of a transition at 120K. Preliminary x-ray diffuse scattering experiment at the Advanced Photon Source of Argonne National Laboratory demonstrates the high quality of one of our crystals and the presence of rod-like diffuse scattering connecting the Bragg peaks …

Magnetoresistance In Non-Magnetic Semimetals And Quantum Wells, Jing Xu

Graduate Research Theses & Dissertations

Magnetic field induced resistance change is conventionally termed as magnetoresistance (MR), which is usually related to magnetism and plays crucial roles in applications such as sensors and storage devices. In a single-band nonmagnetic material, the semiclassical Boltzmann equation approach gives rise to a magnetic field independent resistivity. With the recent discovery of topological materials, extremely large magnetoresistance (XMR) and negative longitudinal magnetoresistance (NLMR) have been observed in a variety of materials. In this dissertation I investigated XMRs in the rare-earth monopnictides (LaSb and YSb), which are non-saturating with increasing magnetic field, accompanying with a turn-on temperature behavior of the magnetoresistivity. …

Two-Dimensional Bloch Electrons In Electric And Magnetic Fields, Edward Aris Diaz Fajardo

Graduate Research Theses & Dissertations

Due to their extraordinary mechanical, and fascinating electronic properties, atomically flat two-dimensional materials are attractive avenues in the search for new and interesting physical phenomena. Symmetry is a powerful tool in studying the dynamics of Bloch electrons in these crystalline solids. Here, using a tight binding description, a systematic scheme is developed to derive the symmetry labels, called irreducible representations (IRs), characterizing the Bloch eigenstates in a crystal, including an extensive discussion on the possibility that these IRs are not always unique. This theory is illustrated using monolayer MoS$_2$ and few-layer graphene as examples. Using this symmetry analysis in conjunction …

Discovery And Study Of Single-Phase And Single-Ion Manganese Perovskite Multiferroics, Kamal Chapagain

Graduate Research Theses & Dissertations

Multiferroic materials having unusual properties of simultaneous presence of ferroelectricity (FE) and magnetism, such that FE can be controlled by magnetic field and magnetization by electric field have attracted interest due to their promising applications in electrically controllable microwave elements, magnetic field sensors, and possibly in spintronics. In this dissertation, the single phase and single ion multiferroic properties of the ceramic oxide antiferromagnets (AFM) Sr1-xBax Mn1-yTiyO3 with perovskite structure are discussed. These compounds were designed and developed in our laboratory by understanding critical parameters controlling FE and magnetic properties, advancing the synthesis processes, studying the structural behavior and intricate transitions, …

Diffuse Scattering And Local Order In Lead-Based Relaxor Ferroelectrics, Matthew J. Krogstad

Graduate Research Theses & Dissertations

Relaxor ferroelectrics are characterized by their dielectric permittivity, and some of these materials display outstanding electromechanical coupling, a property that makes them useful in applications from sonar and ultrasound to precision actuators. However, there is a surprising lack of consensus regarding the local structure of these materials and how it relates to their useful bulk properties. A common feature of many proposed mechanisms is the importance of short-range order differing from the long-range symmetry of the material. Such a difference between short-range and long-range order makes these materials ideal candidates for study via diffuse scattering, a technique sensitive to differences …