Bulletin of the American Physical Society
2006 Texas Section of the APS Joint Fall Meeting
Thursday–Saturday, October 5–7, 2006; Arlington, Texas
Session NM1: Nanomaterials and Magnetism I |
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Chair: Ping Liu, University of Texas at Arlington Room: UT Arlington, University Center San Saba |
Friday, October 6, 2006 10:30AM - 10:42AM |
NM1.00001: Magnetic Phase Diagram of CeMnCuSi$_{2}$ Gan Liang, F. Yen, Mark Croft Field and temperature dependent magnetization measurements on polycrystalline CeMnCuSi$_{2}$ reveal the Mn moments in this compound exhibit ordering with a ferromagnetic (FM) component ordered instead of the previously reported purely antiferromagnetic (AFM) ordering. The FM ordering temperature, $T_{c}$, is about 120 K and almost unchanged with external fields up to 50 kOe. Furthermore, an AFM component is observed to be present in this phase, and its orientation is modified rapidly by the external magnetic field. The Ce $L_{3}$-edge x-ray absorption result shows that the Ce ions in this compound are nearly trivalent. Large thermomagnetic irreversibility is observed between the zero-field-cooled (ZFC) and field-cooled (FC) $M(T)$ curves below $T_{c}$ indicating strong magnetocrystalline anisotropy in the ordered phase. At 5 K, a metamagnetic type transition is observed to occur at a critical field of about 8 kOe, and this critical field decreases with increasing temperature. Based on these results, a magnetic phase diagram is constructed for CeMnCuSi$_{2}$. [Preview Abstract] |
Friday, October 6, 2006 10:42AM - 10:54AM |
NM1.00002: Magnetic properties of FeNi/Gd and Ni/Gd multilayers Maria R. Hossu, Ali R. Koymen Magnetic properties of FeNi/Gd and Ni/Gd multilayers have been studied as a function of temperature. Magnetic measurements prove that multilayers studied (20-60{\AA} layer thickness) have ferrimagnetic behavior and magnetic thermal hysteresis .M (T) has two different minima as temperature is cycled due to first order magnetic phase transition. Temperature difference up to 20K between these minima was observed for both systems having the same TM/Gd ratio. The temperature interval can be controlled with the external magnetic field magnitude. The Ni diffusion into Gd is different for the studied systems, changing the interface coupling and hence the mechanism of the phase transitions during the cooling and heating cycles. [Preview Abstract] |
Friday, October 6, 2006 10:54AM - 11:06AM |
NM1.00003: Empirical Findings of Gas Exchange with Carbon Nanotubes using SRS RGA100 James Roberts, Aman Anand, Don Henley, Jai Dahiya An ultrahigh Vacuum study on the emission of various atmospheric as well as inert gases from Single Walled Carbon Nanotubes have been studied using the SRS RGA 100 Analyzer. A 12.2 cm wavelength of microwaves was used to couple with $\sim $30 mg of Single Walled Carbon Nanotubes subjected to a very high vacuum. Generation of plasma due to the quarter wavelength coupling of the intense microwaves was observed which followed with an increased percent emission of atmospheric gases. A wary study is required in interpreting the results of the residual gas analysis of the out-gassed molecular species from the surface desorbed carbon Nanotubes due to the microwave heating. The technique of molecular orbital excitations of the out gassed species of the gases from Nanotubes can have series of spurious results obtained through the electronic control unit of the Residual Gas Analyzer. The electronic ionization of these transient molecular species can have a dual meaning of the atomic mass units of the emitted gases. The Analog Mode plots of the emission obtained from the Residual Gas Analyzer can have a serious implication over the analysis of the results. [Preview Abstract] |
Friday, October 6, 2006 11:06AM - 11:18AM |
NM1.00004: From Maya Blue to 21st century materials -- a spectroscopic study Felicia Manciu, Layra Reza, Brenda Torres, Lori Polette, Russell Chianelli Maya Blue is a famous indigo-based pigment produced by the ancient Mayas. Samples for the present work are made by a synthetic route, and demonstrate similar chemical stability as the ancient Maya Blue samples. Since no direct proof exists that the indigo chemically binds to the inorganic palygorskite lattice, there is still controversy on the resting place of the indigo molecules; $i.e.$ are they in the channels of palygorskite, on the surface, or both. Our analysis by FT-Raman and FT-IR spectroscopy proves the partial elimination of the selection rules for the centrosymmetric indigo, and shows the disappearance of the indigo N-H bonding, as the organic molecules incorporate into palygorskite material. Infrared data confirm the loss of zeolitic water and a partial removal of structural water after the heating process. Evidence of bonding between cationic aluminum and indigo through nitrogen is revealed by FT-Raman measurements. X-Ray photoemission spectroscopy and near-edge X-ray absorption fine structure studies performed at Stanford Synchrotron Radiation Laboratory support the aluminium bonding to the organic molecules. The oxygen carbonyl is also believed to interact with the metal. [Preview Abstract] |
Friday, October 6, 2006 11:18AM - 11:30AM |
NM1.00005: Enhancing Inter-phase Exchange Coupling in SmCo$_{5}$/Co Nanocomposite Materials Dangxin Wu, Qiming Zhang, J.P. Liu Exchange-coupled hard/soft phase nanocomposite magnets were proposed to increase the maximum energy product by combining the large anisotropy of hard phase materials and the high saturation magnetization of soft phase materials. To understand the inter-phase exchange coupling is very important for design of nanocomposite magnets. In this work, we performed first-principles calculations to investigate the inter-phase exchange coupling between hard phase SmCo$_{5}$ and soft phase Co using superlattice model. The calculations were based on Density Functional Theory, using projector augmented wave (PAW) method and linear-muffin-tin-orbital (LMTO) method in the atomic sphere approximation. The atomic structures were optimized and the electronic ground state was obtained. Then the noncollinear magnetic calculations were performed to calculate the exchange interactions. We found that the total energy is a quadratic function of angle (\textit{$\theta $}) between the directions of magnetic moments of hard phase and middle layer of soft phase. We found that Fe doped soft phase strengths the exchange coupling between SmCo$_{5}$/Co in our models, which in turn may lead to higher maximum energy product. [Preview Abstract] |
Friday, October 6, 2006 11:30AM - 11:42AM |
NM1.00006: Unusually High Beryllium Diffusion in GaAs$_{1-x}$N$_{x}$(x$<<$0.01) Wenkai Zhu, Alex Freundlich In this study, Beryllium diffusion in nitrogen doped gallium arsenide GaAs$_{1-x}$N$_{x}$ (x$<<$0.01) epilayers have been investigated for Be concentrations ranging from 5x10$^{17}$cm$^{-3}$ to 5x10$^{19}$cm$^{-3}$. Post thermal annealings are implemented to extract the temperature dependence of diffusion profiles. Be and carrier concentration profiles are extracted using secondary ion mass spectroscopy and electrochemical capacitance voltage measurements respectively. Diffusivities are extracted by fitting experimental profiles using a model derived from Fick's diffusion law. The study reveals an abnormally high Beryllium diffusivities exceeding by one to two order of magnitudes those encountered in GaAs and a significant reduction of diffusion activation energies 0.5 eV. [Preview Abstract] |
Friday, October 6, 2006 11:42AM - 11:54AM |
NM1.00007: Plasmonic Band Gap Manipulation in Silver Nanogratings Erin Beitel, Jennifer Steele Metallic structures with subwavelegth features can support optical resonances of their conduction electrons, called surface plasmons. On periodic substrates, it is possible to excite simultaneous counterpropagating plasmon waves, which superimpose to form a standing wave. This standing wave has two possible energetic configurations, which defines a plasmonic band gap in the plasmon dispersion. In this study, silver nanogratings were functionalized with different carbon chain length alkanethiols so that the surface chemistry remains constant as the dielectric environment of the silver wires was changed. By monitoring both the surface plasmon energy and the plasmonic band gap, we hope to differentiate between the effects of the surface chemistry and the dielectric environment. The silver nanogratings were fabricated using a passivative microcontact printing method. Functionalization was done with alkanethiols of varying carbon chain lengths to create self-assembled monolayers (SAMs). We have tracked the effect of these molecules on the plasmon energy and band gap. [Preview Abstract] |
Friday, October 6, 2006 11:54AM - 12:06PM |
NM1.00008: XPS Study of Nitrided Hf-based high-k dielectrics F.S. Aguirre-Tostado, A. Herrera-Gomez, M.J. Kim, B.E. Gnade, R.M. Wallace, M.A. Quevedo-Lopez, P.D. Kirsch Nitridation of SiO$_2$ has been demonstrated to increase the dielectric constant of the resulting SiON dielectric allowing further scaling of conventional CMOS devices. Nitridation of Hf-based high-k dielectrics such as HfSiO and HfO$_2$ also results in increased dielectric constant. Besides increased k, nitrogen incorporation in Hf-based dielectrics increases films thermal stability. In this work we systematically study the incorporation of nitrogen in HfSiO and HfO$_2$ using plasma assisted nitridation and thermal treatments The nitrogen concentration and chemical interactions are studied using x-ray photoelectron spectroscopy and x-ray diffraction. The role of nitrogen on the electrical properties is also discussed. [Preview Abstract] |
Friday, October 6, 2006 12:06PM - 12:18PM |
NM1.00009: Landau-Lifshitz or Gilbert Damping of Ferromagnetic Magnetization Wayne Saslow Two apparently equivalent ways of incorporating damping of the magnetization in ferromagnets were given by Landau-Lifshitz and by Gilbert. With the advent of spin-transfer torque in a non-uniform magnet there is now a way to distinguish between them. We present arguments and derivations in support of L-L and against Gilbert: (1) if, as widely believed, the spin-torque is adiabatic, then only L-L can fit the data; (2) irreversible thermodynamics supports L-L; (3) Gilbert's derivation will be shown to have a number of basic flaws and assumptions; (4) simple Fokker-Planck-like derivation of the damping shows it to be L-L. [Preview Abstract] |
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