Fabrication and Control of Magnetic Pd,Fe Thin Film Heterostructures.

The goal of this dissertation research is to investigate the use of multiferroic (ferroelectric- ferromagnetic) thin-film interfaces to control the magnetization in materials of interest for perpendicular recording. We explore the relationship between magnetization and structure in thin films of Fe/Pd compounds deposited onto ferroelectric BaTiO3 substrates. Utilizing magnetostrictive coupling, the magnetism of a magnetic film was controlled by the epitaxial strain at the film/substrate interface. BaTiO3 is particularly favorable as it develops a significant elongation along the tetragonal c-axis as a result of symmetry breaking at the cubic to tetragonal phase transition. A novel aspect of the work is to tune the Curie point of the ferromagnetic transition to match the ferroelectric Curie point of the substrate, so that the magnetostrictive effect is maximized. This is achieved by alloying Fe with Pd to produce a Pd3Fe compound. We report for the first time, the elastic control of the perpendicular magnetic anisotropy of Palladium-Iron (Pd,Fe) films deposited onto a barium-titanate (BaTiO3) (100) substrate. Using Magneto-optic Kerr Effect magnetometry, we observed the behavior of the magnetization through the tetragonal-to-cubic phase transition of the BaTiO3 substrate. We found that such films exhibited in-plane magnetization reversal below the T-C transition temperature, and out-of-plane magnetization reversal above the transition. This change in behavior demonstrates the elastic control of the perpendicular magnetic anisotropy of the deposited Pd,Fe film. In addition, we grew an ordered FePd3 film on SrTiO3 using the inter-diffusion of an Fe/Pd multilayer heterostructure. Each layer was deposited using Ultra-High Vacuum deposition. Utilizing in-situ RHEED (Reflection High Energy Electron Diffraction), we observed that each deposited layer was both ordered and exhibited the crystalline structure of the bulk material. Once deposited, the multi-layer heterostructure was heated above the FePd$_{3}$ formation temperature. Upon heating, the RHEED pattern began to exhibit the crystalline structure of FePd3. Using X-ray Diffraction analysis and MOKE magnetometry, we found that the epitaxial film consisted primarily of FePd3. This example of atomic layer epitaxy of Fe, Pd alloys represents a successful approach to forming high quality magnetic heterostructures on perovskites with excellent control over their composition and structural ordering.PhDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120869/1/reneehar_1.pd

Characterization of polygrama green photopolymer for Compact Optoelectronic Integrated Neural (COIN) coprocessor applications

Includes bibliographical references (leaves 33-34).Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2008.The research described in this thesis is a portion of a larger project within the Photonic Systems Group at MIT to design Compact Optoelectronic Integrated Neural (COIN) co processor [13]. The choice of photopolymers is critical in determining the performance of COIN processors as we look at ways to increase the diffraction efficiency. The focus of this research was to optically characterize Polygrama Green, a photopolymer that is sensitive to green light (514 nm). We were able to plot diffraction efficiency versus the exposure energy density for a series of gratings. We found the maximum diffraction efficiency to be that of the 678 mJ/cm2 grating with a value of 29.5%. We were able to fit the data to a sin2(x) curve with a X2- value of 20.79. We concluded that this somewhat high X2-value is due to our low number of data points. However, using Kogelnik's equation and the measured diffraction efficiency of each grating, we were also able to calculate the An, of each grating. This analysis shows that Polygrama Green seems to be a promising candidate for the photopolymer used in subsequent optoelectronic neural network applications.by Renee M. Harton.S.B

IRBs and Best Practices for Ethical Data Sharing

Materials associated with 2017-07-30 sessio

Coherent J/ψ photoproduction in ultra-peripheral Pb–Pb collisions at √sNN=2.76 TeV

The ALICE Collaboration has made the first measurement at the LHC of J/ψ photoproduction in ultra-peripheral Pb–Pb collisions at sNN=2.76 TeV. The J/ψ is identified via its dimuon decay in the forward rapidity region with the muon spectrometer for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 55 μb−1. The cross section for coherent J/ψ production in the rapidity interval −3.6<y<−2.6 is measured to be dσJ/ψcoh/dy=1.00±0.18(stat)−0.26+0.24(syst) mb. The result is compared to theoretical models for coherent J/ψ production and found to be in good agreement with those models which include nuclear gluon shadowing

Long-range angular correlations of π, K and p in p–Pb collisions at sNN\sqrt{s_{NN}} = 5.02 TeV

Angular correlations between unidentified charged trigger particles and various species of charged associated particles (unidentified particles, pions, kaons, protons and antiprotons) are measured by the ALICE detector in p-Pb collisions at a nucleon--nucleon centre-of-mass energy of 5.02 TeV in the transverse-momentum range 0.3 < $p_T$ < 4 GeV/c. The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range |$\eta_{lab}$| < 0.8. Fourier coefficients are extracted from the long-range correlations projected onto the azimuthal angle difference and studied as a function of $p_T$ and in intervals of event multiplicity. In high-multiplicity events, the second-order coefficient for protons, $v_2^p$, is observed to be smaller than that for pions, $v_2^\pi$, up to about $p_T$ = 2 GeV/c. To reduce correlations due to jets, the per-trigger yield measured in low-multiplicity events is subtracted from that in high-multiplicity events. A two-ridge structure is obtained for all particle species. The Fourier decomposition of this structure shows that the second-order coefficients for pions and kaons are similar. The $v_2^p$ is found to be smaller at low $p_T$ and larger at higher $p_T$ than $v_2^\pi$, with a crossing occurring at about 2 GeV. This is qualitatively similar to the elliptic-flow pattern observed in heavy-ion collisions. A mass ordering effect at low transverse momenta is consistent with expectations from hydrodynamic model calculations assuming a collectively expanding system.Angular correlations between unidentified charged trigger particles and various species of charged associated particles (unidentified particles, pions, kaons, protons and antiprotons) are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV in the transverse-momentum range $0.3 < p_{\rm T} < 4$ GeV/$c$. The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range $|\eta_{\rm lab}|<0.8$. Fourier coefficients are extracted from the long-range correlations projected onto the azimuthal angle difference and studied as a function of $p_{\rm T}$ and in intervals of event multiplicity. In high-multiplicity events, the second-order coefficient for protons, $v_2^p$, is observed to be smaller than that for pions, $v_2^\pi$, up to about $p_{\rm T} = 2$ GeV/$c$. To reduce correlations due to jets, the per-trigger yield measured in low-multiplicity events is subtracted from that in high-multiplicity events. A two-ridge structure is obtained for all particle species. The Fourier decomposition of this structure shows that the second-order coefficients for pions and kaons are similar. The $v_2^p$ is found to be smaller at low $p_{\rm T}$ and larger at higher $p_{\rm T}$ than $v_2^pi$, with a crossing occurring at about 2 GeV. This is qualitatively similar to the elliptic-flow pattern observed in heavy-ion collisions. A mass ordering effect at low transverse momenta is consistent with expectations from hydrodynamic model calculations assuming a collectively expanding system.Angular correlations between unidentified charged trigger particles and various species of charged associated particles (unidentified particles, pions, kaons, protons and antiprotons) are measured by the ALICE detector in p–Pb collisions at a nucleon–nucleon centre-of-mass energy of 5.02 TeV in the transverse-momentum range 0.3<pT<4 GeV/c . The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range |ηlab|<0.8 . Fourier coefficients are extracted from the long-range correlations projected onto the azimuthal angle difference and studied as a function of pT and in intervals of event multiplicity. In high-multiplicity events, the second-order coefficient for protons, v2p , is observed to be smaller than that for pions, v2π , up to about pT=2 GeV/c . To reduce correlations due to jets, the per-trigger yield measured in low-multiplicity events is subtracted from that in high-multiplicity events. A two-ridge structure is obtained for all particle species. The Fourier decomposition of this structure shows that the second-order coefficients for pions and kaons are similar. The v2p is found to be smaller at low pT and larger at higher pT than v2π , with a crossing occurring at about 2 GeV/c . This is qualitatively similar to the elliptic-flow pattern observed in heavy-ion collisions. A mass ordering effect at low transverse momenta is consistent with expectations from hydrodynamic model calculations assuming a collectively expanding system