Bulletin of the American Physical Society
Joint Fall 2011 Meeting of the Texas Sections of the APS, AAPT, and Zone 13 of the SPS
Volume 56, Number 7
Thursday–Saturday, October 6–8, 2011; Commerce, Texas
Session N5: Condensed Matter Physics and Materials Research V |
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Chair: Christopher Littler, University of North Texas Room: Science Building 127 |
Saturday, October 8, 2011 12:05PM - 12:17PM |
N5.00001: Simulation and Modeling of Positrons and Electrons in advanced Time-of-Flight Positron Annihilation Induced Auger Electron Spectroscopy Systems Prasad Joglekar, Karthik Shastry, Suman Satyal, Alexander Weiss Time of Flight Positron Annihilation Induced Auger Electron Spectroscopy (T-O-F PAES) is a highly surface selective analytical technique in which elemental identification is accomplished through a measurement of the flight time distributions of Auger electrons resulting from the annihilation of core electron by positrons. SIMION charged particle optics simulation software was used to model the trajectories both the incident positrons and outgoing electrons in our existing T-O-F PAES system as well as in a new system currently under construction in our laboratory. The implication of these simulation~regarding the instrument design and performance are discussed. [Preview Abstract] |
Saturday, October 8, 2011 12:17PM - 12:29PM |
N5.00002: Behavior of Phonons in the Optical Properties of Magnetron Sputtered ZnO Sandeep Sohal, Yahya Alivov, Zhaoyang Fan, Mark Holtz Resonance Raman scattering and photoluminescence (PL) emission measurements have used to study the temperature dependence of phonons in the wide band gap semiconductor ZnO. There are strong resonance Raman features observed with excitation wavelength 363.8 nm (photon energy 3.409 eV). Near room temperature, this photon energy correspond to in-coming resonance as confirmed by absorption spectrum. Broad PL is seen at room temperature with peak position at 3.25 eV. This coincides with the overtone of longitudinal optic (LO) band. Strong electron-phonon interactions in ZnO allow six LO phonon orders to be observed in Raman spectrum. Temperature dependence of the LO phonon energy is described by a two phonon decay mechanism with energies 100 and 496 cm$^{-1}$. The temperature dependence of the PL shift is described by physical approach and two vibrational energies corresponding to the center of the acoustic and optic bands in the DOS, i.e., 125 and 500 cm$^{-1}$. LO phonon sidebands (PSBs) are also observed at low temperature (23-100K). The temperature shift of the PSB energies are interpreted on the basis of the band gap shift combined with established theory for the PSBs. [Preview Abstract] |
Saturday, October 8, 2011 12:29PM - 12:41PM |
N5.00003: Formation of Cobalt Oxide at Co/CuO Interface A.R. Chourasia, Justin Merritt, Mikel Morgan The chemical interaction at the cobalt/copper oxide interface has been investigated by the technique of x-ray photoelectron spectroscopy. Thin films of copper were deposited on titanium substrates. The film was oxidized in an atmosphere of oxygen in a quartz tube furnace. Following the oxidation, the sample was loaded in the deposition chamber for further processing. A thin film of cobalt with thickness 0.5 nm was deposited on the copper oxide. The interface was characterized in situ. The cobalt 2p region, the copper 2p region, and oxygen 1s region has been investigated. The results show the formation of cobalt oxide with the reduction of copper oxide to copper. A 0.3 nm of cobalt was further deposited on the sample to check for the uniform coverage. The second deposition showed the presence of elemental cobalt on the sample. The study shows chemical reactivity at the interface and that the subsequent layer of cobalt does not get oxidized. [Preview Abstract] |
Saturday, October 8, 2011 12:41PM - 12:53PM |
N5.00004: Micromagnetic simulations of the transition between vortex and single-domain magnetization states in sub-100 nm nanodots Andrew T. King, Igor V. Roshchin The magnetic vortex state in nanodots has demonstrated unique properties, which may improve magnetic data storage technologies. To utilize these properties, we must understand magnetic switching to and from the vortex state. We used a ``rigid-vortex approximation'' to calculate the total magnetic energy of a nanodot for various magnetic configurations. This was done for 20 nm-thick iron nanodots with different diameters (30, 40, 65, and 80 nm) as a function of applied magnetic field. By analyzing the energy landscape for different magnetic configurations, we calculated the energy barrier for switching from the vortex to the single-domain state (vortex annihilation) and the converse (vortex nucleation). The applied fields required to overcome these two barriers are compared to those obtained from the simulations directly and to the experimental values.\footnote{R. K. Dumas, C.-P. Li, I. V. Roshchin, I. K. Schuller and K. Liu, Appl. Phys. Lett. \textbf{91}, 202501 (2007). } The role of the thermal fluctuations in the temperature dependence of these critical fields will be discussed by comparison of the energy barriers with the thermal energy, kT. [Preview Abstract] |
Saturday, October 8, 2011 12:53PM - 1:05PM |
N5.00005: Effect of Cu Layer on FeMn Magnetic Properties Dogan Kaya, Priyanga Jayathilaka, Casey W. Miller, Igor V. Roshchin Growing demand for high-density memories requires new materials for magnetoresistive sensors in the read heads. FeMn has a great potential to be used for exchange-biasing the reference layer in the read heads. One of the crucial puzzles is the origin of the uncompensated magnetization in the antiferromagnetic FeMn. To study that, we use Cu layer to affect the magnetic properties of FeMn and its uncompensated magnetization. The multilayers of Ta(50 {\AA})/[FeMn(50 {\AA} -- 150 {\AA})/Cu(50 {\AA})]$_{10}$/Ta(50 {\AA}) are deposited by UHV DC magnetron sputtering on top of Si/SiO$_{x}$ 3 mm x5 mm substrates. Samples with a single layer of FeMn of the same thickness, Ta(50 {\AA})/FeMn(50 {\AA} -- 150 {\AA})/Ta(50 {\AA}) are used as control samples. The samples are cooled in a field of 7 T and their magnetization is measured using a SQUID magnetometer. All the samples have uncompensated magnetization that exhibits a hysteresis at 10 K. It is found that for the FeMn/Cu multilayers, the hysteresis loops are exchange bias shifted, while FeMn without Cu exhibits no exchange bias. Dependence of coercive field (H$_{c})$, exchange bias (H$_{e})$, and saturated magnetization (M$_{s})$ on the FeMn thickness and on temperature will be discussed. Work is supported by Texas A{\&}M University, TAMU-CONACYT Collaborative Research Program, and by NSF-CAREER. [Preview Abstract] |
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