Bulletin of the American Physical Society
2010 Annual Meeting of the California-Nevada Section of the APS
Volume 55, Number 12
Friday–Saturday, October 29–30, 2010; Pasadena, California
Session C1: Condensed Matter Physics and Materials Science I |
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Chair: Andreas Bill, California State University, Long Beach Room: Building 74 - Beckman Institute Auditorium |
Friday, October 29, 2010 2:00PM - 2:12PM |
C1.00001: Spin transport and Relaxation in Graphene Wei Han, Roland Kawakami Graphene is an attractive material for spintronics due to the low intrinsic spin-orbit and hyperfine coupling, which should lead to excellent spin transport properties. We investigated the spin injection, transport and relaxation in single layer graphene (SLG) using non-local magnetoresistance (MR) measurements. Spin injection is performed using either transparent contacts (Co/SLG) or tunneling contacts (Co/MgO/SLG). With tunneling contacts, the non-local MR is increased by a factor of $\sim $1000 and the spin injection/detection efficiency is greatly enhanced from $\sim $1{\%} for transparent contacts to 26-30{\%}. Gate tunable spin transport is performed using the SLG properties of gate tunable conductivity and incorporating different types of contacts (transparent and tunneling contacts). Spin relaxation is investigated on SLG spin valves using Hanle measurements. Comparing the measured spin lifetimes for transparent contacts and tunneling contacts, we observed enhanced spin lifetimes for tunneling contacts which indicates that spin relaxation induced by the contacts is important. These developments are important advances for graphene to be used for spin computing or spin logic applications. [Preview Abstract] |
Friday, October 29, 2010 2:12PM - 2:24PM |
C1.00002: Growth of Iridium and Silver on Ge(111) Studied by STM Marshall van Zijll, Cory Mullet, Emilie Huffman, Shirley Chiang We have used scanning tunneling microscopy (STM) to characterize the growth of iridium and silver onto Ge(111) as a function of coverage and annealing temperature. Ir was deposited onto the Ge(111) c(2x8) surface at different coverages less than 1ML. The Ir forms islands with a ($\surd $3x$\surd $3)R30\r{ } phase and island size increasing with increasing annealing temperature. Stranski-Krastanov growth was observed at most coverages. Ag deposited onto the Ge(111) c(2x8) surface and annealed at 450K forms both a (4x4) phase and a (3x1) phase. The Ge(111) surface reorganizes to a (2x2) phase after deposition of both Ir and Ag. High resolution images have been obtained allowing direct observation of the different phases. [Preview Abstract] |
Friday, October 29, 2010 2:24PM - 2:36PM |
C1.00003: Oxidation of nitride surfaces and its effect on device performance Maosheng Miao, Luke Gordon, Justin Weber, Chris Van de Walle Using computational methods based on density functional theory and Schr\"{o}dinger-Poisson simulations, we investigate atomistic and electronic structures of oxidized GaN and AlN (0001) surfaces and their effects on the two-dimensional electron gas (2DEG) at AlGaN/GaN heterojunctions. Numerous structures with different oxide coverage and different stoichiometry are examined, and their stability is interpreted in terms of driving mechanisms such as the electron counting rule and oxide-stoichiometry matching. We discuss which structures are likely to form under a variety of oxidation conditions, and show that these structures explain the observed dependence of electron density on thickness and variations of surface barrier height. The surface donor states with distributed and finite density are implemented in Schr\"{o}dinger-Poisson simulations of AlGaN/GaN high electron mobility transistors (HEMTs). The recent experimental observations of an increasing surface barrier height with increasing AlGaN thickness are fit very well by simulations including surface donor levels represented by a constant density of states (DOS) with a density on the order of 10$^{13}$ cm$^{-2}$eV$^{-1}$. The highest occupied surface states are found to be around 1 eV below the conduction-band minimum, which is in good agreement with the first-principles results. [Preview Abstract] |
Friday, October 29, 2010 2:36PM - 2:48PM |
C1.00004: A Far- and Mid-Infrared Study of HMX (octahydro- 1,3,5,7-tetranitro-1,3,5,7-tetrazocine) under High Pressure Michael Pravica, Martin Galley, Eunja Kim, Phillipe Weck, Zhenxian Liu We report two separate synchrotron FTIR measurements of the high explosive HMX at ambient temperature and static high pressure in the far- (100-500 wavenumbers) and mid- (500-3200 wavenumbers) infrared (IR) regions up to 30 GPa. The sample for the far-IR experiment was loaded with no pressure-transmitting medium and the sample for the mid-IR study utilized a KBr pressurizing medium. Two possible phase transitions from beta-HMX at ambient conditions were observed near 5 and 12 GPa (likely into the epsilon phase). A phase transition was observed near 25 GPa probably into the delta phase. Pressure cycling in both experiments found no irreversible damage within this pressure range. [Preview Abstract] |
Friday, October 29, 2010 2:48PM - 3:00PM |
C1.00005: Searching for superconducting Fe-pnictide features in FeAs/GaAs heterostructures Sinead Griffin, Nicola Spaldin Superconducting Fe-pnictide compounds are a class of materials in the limelight, with focus on the FeAs layer to provide insight into their behaviour. We investigate the inclusion of these layers in FeAs/GaAs heterostructures using ab initio density functional theory calculations to search for the superconducting Fe-pnictide properties. We consider the effect of increasing Fe content and Fe-As arrangements on the magnetic and electronic properties in an effort to reproduce Fe-pnictide type magnetic ordering and Fermi surfaces. [Preview Abstract] |
Friday, October 29, 2010 3:00PM - 3:12PM |
C1.00006: Magnetic Proximity Effect in Nb-Py-Nb Trilayers Jill Pestana, Jiyeong Gu Proximity effect in ferromagnet/superconductor systems has become a center of attention recently. So far most of the work focused on the superconducting property change by magnetism in the hybrid system but only few researches were focused on the magnetic property change by superconductivity. In our current work we focused on the magnetic property change of the system by superconductivity when the system goes through the superconducting transition. We have investigated Nb-Py (Permalloy; NiFe)-Nb trilayers. Nb-Py-Nb thin film samples with different Py layer and top Nb layer thicknesses were fabricated by using Multi-target sputtering system. Magnetization and resistivity were measured by Physical Property Measurement System using the Vibrating Sample Magnetometer (VSM) option. Magnetization changed when the system goes through the superconducting transition. We discuss the magnetic correlations between ferromagnetic and superconducting layers. In addition to the VSM option, the Alternating Current Measurement System (ACMS) method was used to compare the magnetization results. [Preview Abstract] |
Friday, October 29, 2010 3:12PM - 3:24PM |
C1.00007: Depth-resolved electronic structure of an LSMO/STO/LSMO magnetic tunnel junction via standing-wave excited angle-resolved photoemission Alexander Gray, Mark Huijben, See-Hun Yang, Charles Fadley We have quantitatively determined electronic, chemical and structural profile of the LSMO/STO/LSMO magnetic tunneling junction via soft and hard x-ray standing-wave excited photoemission, x-ray absorption and x-ray reflectivity, in conjunction with x-ray optical and core-hole multiplet theory. Epitaxial multilayer samples consisting of 48 and 120 bilayers of LSMO and STO, each nominally four unit cells thick, were studied. By varying incidence angle around the Bragg condition, the standing wave is moved through the sample. Depth-resolved standing-wave excited soft x-ray ARPES shows distinctly different \textbf{\textit{k}}-space maps of Mn 3d e$_{g}$ and t$_{2g}$ states from the bulk-like and interface-like regions of the LSMO. The soft x-ray photoemission data exhibit a shift in the position of the Mn 3p peak which is not observed for the peaks in any other element; combined with core-hole multiplet theory calculations incorporating Jahn-Teller distortion, these results indicate a change in the Mn bonding state near the STO/LSMO interface. [Preview Abstract] |
Friday, October 29, 2010 3:24PM - 3:36PM |
C1.00008: Tuning the Coercivity in Low-Dimensional Magnetic Thin Films Isaac Bonyuet, Brian Cacha, Matthew Byrne, Jacob Kalmanir, Thomas Gredig Low-dimensional magnetism has played an important role in theoretical physics; however, experimentally it is more challenging because of difficulty in achieving statistically significant sample sizes. Recently, iron stripes have been prepared on terraced substrates with line separations of about 10nm. In order to reduce the iron chain separation to under 2nm, we prepared thin films of self-assembling organic molecules. Results of low-temperature ferromagnetic response from iron phthalocyanine thin films that form quasi one-dimensional chains are presented. The magnetic hysteresis loops indicate long-range ferromagnetic interaction below 4.5 K and exhibit a memory state. The coercivity could be correlated with the grain size of the iron phthalocyanine thin film. The larger coercivity is attributed to longer chains that are formed in larger grains. [Preview Abstract] |
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