Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 59, Number 11
Friday–Saturday, October 17–18, 2014; Orem, Utah
Session K1: Condensed Matter IV |
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Chair: Phil Matheson, Utah Valley University Room: Science Building 031 |
Saturday, October 18, 2014 1:15PM - 1:39PM |
K1.00001: Study of spin-orbit torques in magnetic bilayer Invited Speaker: Xin Fan In recent years, the spin-orbit interaction in magnetic/nonmagnetic bilayer has attracted intensive attention, which opens a new path to electrically control magnetism. The spin-orbit interaction describes the coupling between electron charge and spin, which is the fundamental building block of magnetism. It is found that an in-plane current through the bilayer can generate a spin-orbit torque that manipulates the magnetization of the magnetic layer [1,2]. The efficiency of this effect mainly depends on the property of the nonmagnetic layer, which is typically stronger in materials with strong spin-orbit interactions. In this talk I will review the recent development and discuss about some controversies in this field. I will also present our recent efforts on the accurate detection of the spin-orbit torque [3].\\[4pt] [1] Liu, L.\textit{ et al.} Spin-Torque Switching with the Giant Spin Hall Effect of Tantalum. \textit{Science} \textbf{336}, 555-558 (2012).\\[0pt] [2] Miron, I. M.\textit{ et al.} Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection. \textit{Nature} \textbf{476}, 189-U188 (2011).\\[0pt] [3] Fan, X. \textit{et al.} Quantifying interface and bulk contributions to spin--orbit torque in magnetic bilayers. \textit{Nature Communications }\textbf{5}, 3042 (2014) [Preview Abstract] |
Saturday, October 18, 2014 1:39PM - 1:51PM |
K1.00002: Solving the Ginzburg-Landau Equation of Superconductivity Using a Galerkin Method Alden Pack, Mark Transtrum A hallmark feature of superconductors, known as the Meissner effect, is the expulsion of applied magnetic fields from the superconducting material. This phenomenon can be modeled by the Ginzburg-Landau equations of superconductivity. These equations are a set of nonlinear, partial differential equations relating the magnetic vector potential and the superconducting order parameter. Assuming a transverse symmetry and a steady state, these equations reduce to one-dimensional, ordinary differential equations. We solve these differential equations using a Galerkin method which projects the solution onto a finite set of basis function. We explore convergence properties for different choices of bases. [Preview Abstract] |
Saturday, October 18, 2014 1:51PM - 2:03PM |
K1.00003: Unavoidable Asymmetries in Distributions of Electric Field Gradients Frank Sullivan, Phil Matheson, William E. Evenson Evenson, et. al. [1] have addressed topologically appropriate coordinates for probability distribution functions (PDFs) used to describe electric field gradients (EFGs) in solid materials. In many situations of interest, such as Perturbed Angular Correlation (PAC) studies, the distribution of material defects that give rise to EFGs are nearly amorphous. Czjzek, et al. [2] provided a theoretical foundation for such a distribution of EFGs in an amorphous solid. However, most applications of his work seem to ignore the inherent asymmetry of the PDF that must arise from nearest neighbor defects in real materials, whether or not that material is amorphous. Such asymmetries may make it difficult or impossible to remove correlations between EFG components, thwarting attempts to find separable, independent PDFs such as are used to explore hyperfine phenomena. We use Evenson's parameterization of the EFG coordinates to study the asymmetries introduced into the PDFs of cubic materials, looking to see how strongly these asymmetries affect attempts to find separable PDFs for use in characterizing PAC spectra. \\[4pt] [1] William E. Evenson, et. al., \textit{Topologically appropriate coordinates for (V$_{zz}, \eta$) joint probability distributions}, in preparation.\\[0pt] [2] G. Czjzek, et al., \textit{Atomic coordination and the distribution of electric field gradients in amorphous solids}, Phys. Rev. B, vol. 23, (6), 15 Mar. 1981. [Preview Abstract] |
Saturday, October 18, 2014 2:03PM - 2:15PM |
K1.00004: Visualising FCC Binary Derivative Superstructures Tim Wendler, Gus Hart We present a way to visualize multiple crystal structures in such a way that one can see their common origin. Binary FCC systems at non-fixed concentrations are shown to have periodicity on a larger scale. Enumerating derivative superstructures is useful in the search for naturally occurring crystal structures as the super-cells are based off primitive cells that are already known to exist. The visualization model we present is designed to display the research results accurately and stimulate the mind's eye promoting useful inquisition for future research. [Preview Abstract] |
Saturday, October 18, 2014 2:15PM - 2:27PM |
K1.00005: Discovering physics using signal processing Chandramouli Nyshadham, Gus L.W. Hart Compressive sensing (CS) is a novel technique developed recently in the field of signal processing. In signal processing, one samples a signal amplitude along the time axis and reconstructs it from the measured samples. In order to recover the measured signal one needs to satisfy the ``Shannon-Nyquist theorem'' which tells that the sampling rate should be at least twice the maximum frequency present in the signal. CS allows one to recover a sparse signal with a far fewer measurements than required by the Shannon-Nyquist theorem. We can utilize the CS paradigm to ``recover'' a physical model from just a few measurements or calculations[1]. In this talk, I will present a simple understanding of the concept of compressive sensing and its usage in realizing physical models. \\[4pt] [1] Lance J. Nelson, Gus L. W. Hart, Fei Zhou and Vidvuds Ozoli\c{n}\v{s}, ``Compressive sensing as a paradigm for building physical models,'' Phy. Rev. B. 87, 035125 (2013). [Preview Abstract] |
Saturday, October 18, 2014 2:27PM - 2:39PM |
K1.00006: Potts Model: A Simple Way to Discover New Alloys William Keele Metal alloys are used for many different things in our world, such as jets, engines, and other machinery. We aim to simulate alloys by computer modeling, rather than physical experimentation. The Potts Model and Ising Model are different methods to simulate an alloy in a simple way. For the Ising Model, one takes a lattice of points with each point having a spin value pointing up or down, or q=2, with each spin representing a different type of atom. The Potts Model is a generalized form of the Ising, so we explore other spin values in the same lattice as q goes from 3 to infinity. One key aspect to studying the Potts and Ising Models is to see how the spins of a certain lattice may affect those spins around it. In my own experiments with the Potts Model, I modeled systems ranging from q=3 to q=10 and reported Magnetization, Energy, and Specific Heat as a function of temperature. [Preview Abstract] |
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