Bulletin of the American Physical Society
12th Annual Meeting of the Northwest Section of the APS
Volume 55, Number 6
Friday–Saturday, October 1–2, 2010; Walla Walla, Washington
Session C3: Condensed Matter I |
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Chair: Yves Idzerda, Montana State University Room: Brattain Auditorium, Science 100 |
Friday, October 1, 2010 1:30PM - 2:06PM |
C3.00001: Superconductivity and Magnetism in Pnictides Invited Speaker: Magnetic atoms are not likely to be the main structure elements in superconducting materials, since they tend to destroy superconducting Cooper pairs. However, in recent times several magnetically-active composites appeared that also exhibit superconducting properties. I will discuss the most recent class of Fe-based metallic materials with superconducting $T_c$ up to 55 K that is currently being intensively investigated. Questions of the pairing glue, symmetry and structure of the condensed state in the Fe-based superconductors is still open despite experimental and theoretical efforts. Contributors to this uncertainty are: (a) the multi-band nature of electronic structure; (b) complex phase diagram where superconductivity appears close and sometimes together with magnetism; (c) several different families of compounds with different physical properties. In this talk I will focus on the exciting proximity of two electronic orders: superconducting (SC) and magnetic spin-density-wave (SDW) states. I will show how the interplay between these two states depends on the Fermi surface shape, the order parameter structure, the strength of SC and SDW interactions, and what can be concluded about the superconductivity on the basis of this interplay. [Preview Abstract] |
Friday, October 1, 2010 2:06PM - 2:18PM |
C3.00002: ABSTRACT WITHDRAWN |
Friday, October 1, 2010 2:18PM - 2:30PM |
C3.00003: Ferromagnetism in doped or undoped spintronics nanomaterials You Qiang Much interest has been sparked by the discovery of ferromagnetism in a range of oxide doped and undoped semiconductors. The development of ferromagnetic oxide semiconductor materials with giant magnetoresistance (GMR) offers many advantages in spintronics devices for future miniaturization of computers. Among them, TM-doped ZnO is an extensively studied n-type wide-band-gap (3.36 eV) semiconductor with a tremendous interest as future mini-computer, blue light emitting, and solar cells. In this talk, Co-doped ZnO and Co-doped Cu$_{2}$O semiconductor nanoclusters are successfully synthesized by a third generation sputtering-gas-aggregation cluster technique. The Co-doped nanoclusters are ferromagnetic with Curie temperature above room temperature. Both of Co-doped nanoclusters show positive magnetoresistance (PMR) at low temperature, but the amplitude of the PMRs shows an anomalous difference. For similar Co doping concentration at 5 K, PMR is greater than 800{\%} for Co-doped ZnO but only 5{\%} for Co-doped Cu$_{2}$O nanoclusters. Giant PMR in Co-doped ZnO which is attributed to large Zeeman splitting effect has a linear dependence on applied magnetic field with very high sensitivity, which makes it convenient for the future spintronics applications. The small PMR in Co-doped Cu$_{2}$O is related to its vanishing density of states at Fermi level. Undoped Zn/ZnO core-shell nanoparticle gives high ferromagnetic properties above room temperature due to the defect induced magnetization at the interface. [Preview Abstract] |
Friday, October 1, 2010 2:30PM - 2:42PM |
C3.00004: Atomic ordering in ternary phases having the Al$_{4}$Ba structure Lee Aspitarte, Xiangyu Yin, Randal Newhouse, Gary S. Collins Al$_{4}$Ba is by far the most common intermetallic structure that has a 4:1 ratio of constituent elements. There is one Ba-site and two inequivalent Al-sites. Experiments were carried out to measure quadrupole interactions at dilute $^{111}$In/Cd probe atoms using perturbed angular correlation spectroscopy (PAC) for a number of ternary phases based on Al$_{4}$Ba. One was a sample having composition In$_{2}$Al$_{2}$Ba, with end-member phases Al$_{4}$Ba and In$_{4}$Ba both having the Al$_{4}$Ba structure. The PAC spectrum exhibited two broadened quadrupole interaction signals, indicating that Al and In atoms do not order on the two sublattices. Instead, they appear to locate more or less randomly on the two sublattices, making a ``pseudo-binary'' Al$_{4}$Ba phase. The other sample was BaNiSn$_{3}$, for which it has been reported that Ni-atoms order on half of one of the two Al-sublattices. Indium was expected to prefer to occupy sites of chemically-similar Sn, of which there are two types: one having a quadrupole interaction that is axially symmetric and the other one having lower symmetry. Experiment showed only one signal for a low-symmetry site, but with excellent signal coherence. It is concluded that there is a high degree of atomic ordering in BaNiSn$_{3}$ and that indium impurities in the phase occupy only one of two inequivalent Sn-sites. \textit{Supported in part by the NSF under grant DMR 09-04096 (Metals Program).} [Preview Abstract] |
Friday, October 1, 2010 2:42PM - 2:54PM |
C3.00005: Application of Polypacfit to obtain jump frequencies of probe atoms among sites having collinear EFG axes in Al$_{4}$Ba phases Randal Newhouse, Matthew Zacate, Gary S. Collins The Al$_{4}$Ba structure has two inequivalent Al-sites that have local electric field gradients (EFGs) collinear with a tetragonal crystal axis. Rapid diffusional jumps between the two sites leads to motional averaging of nuclear quadrupole interaction signals, as detected using perturbed angular correlation of gamma rays (PAC). However, unlike in the case of jumps that lead to reorientation of EFG axes and a loss of coherence of quadrupole precessions [1], motional averaging here leads to more subtle effects. A new program, Polypacfit, can be applied for fitting PAC spectra for nuclear relaxation to determine atomic jump frequencies in the Al sublattice. Polypacfit generates a PAC spectrum based on orientations of principal axes of the EFG specified by the user and fits this to experimental data. Polypacfit expands the range of systems in which PAC can be used to obtain diffusion data. \textit{Supported in part by the NSF under grant DMR 09-04096 (Metals).}\\[4pt] [1] M.O. Zacate, A. Favrot and G.S. Collins, Phys. Rev. Lett. \underline {92}, 225901 (2004). [Preview Abstract] |
Friday, October 1, 2010 2:54PM - 3:10PM |
C3.00006: BREAK
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Friday, October 1, 2010 3:10PM - 3:46PM |
C3.00007: Ultraviolet Raman spectroscopy of ferroelectric thin films and superlattices Invited Speaker: Nanoscale ferroelectrics possess essentially different properties compared to bulk materials and provide an opportunity to manipulate and enhance the ferroelectric properties. Vibrational (Raman and infrared) spectroscopies can provide valuable information for understanding the behavior of nanoscale ferroelectrics. However, conventional vibrational spectroscopies operating in visible and infrared range fail to measure the phonon spectra of nanoscale ferroelectric structures because of extremely weak signals and the overwhelming substrate contribution. In this talk, application of ultraviolet (UV) Raman spectroscopy for studies of lattice dynamics and ferroelectric phase transitions in nanoscale ferroelectrics will be presented. UV Raman spectroscopy has been demonstrated to be an effective technique allowing the observation of phonons and determination of the phase transition temperatures in nanoscale ferroelectrics, specifically, BaTiO$_{3}$/SrTiO$_{3}$ superlattices and ultrathin (as thin as 1.6 nm) BaTiO$_{3}$ single layer films. UV Raman studies of the effects of strain and film thickness on phase diagrams in BaTiO$_{3}$/SrTiO$_{3}$ ferroelectric heterostructures will be discussed will be discussed and compared with thermodynamic phase-field model and first principles lattice dynamics calculations. Also, recent results on the effect of strontium non-stoichiometry on ferroelectricity in homoepitaxial SrTiO$_{3}$ films will be presented. [Preview Abstract] |
Friday, October 1, 2010 3:46PM - 3:58PM |
C3.00008: X-ray Absorption spectroscopy and electronic structure calculation of DyScO$_{3}$ Harshawardhan Bhatkar, B. Anderson, M. Finsterbusch, P. Rugheimer, Y.U. Idzerda Dysprosium scandate (DyScO$_{3})$ is of interest for its potential as a substrate for thin film growth of various materials such as EuTiO$_{3}, $SrTiO$_{3}$ BaTiO$_{3}$ and LaSrMnTiO$_{3}$ particularly because it creates biaxial strain due to mismatched lattice constant with those materials affecting their properties. We have used X-ray Absorption Spectroscopy to determine the electronic structure of DyScO$_{3}$. The M$_{4,5}$ edges of Dy and L$_{2,3}$ edges of Sc in DyScO$_{3}$ were investigated against chemically similar materials Dy$_{2}$O$_{3}$ and Sc$_{2}$O$_{3}$ reference powders and compared with theoretical calculations using LCMO multiplet theory. The spectra are well reproduced by calculations with the given atomic structures, an added crystal field and broadening parameters. We find that the Sc L$_{2,3}$ edge in DyScO$_{3}$ is more broadened than in Sc$_{2}$O$_{3}$ and the peak position of Dy M$_{4,5}$ edge in DyScO$_{3}$ is slightly shifted as compared to those in Dy$_{2}$O$_{3}$. [Preview Abstract] |
Friday, October 1, 2010 3:58PM - 4:10PM |
C3.00009: Electrochemical modification of Surface valence - Cr precipitates on LSCF surfaces Martin Finsterbusch, J.A. Schaefer, B.C. Eigenbrodt, R.A. Walker, A. Lussier, Y.U. Idzerda Interactions of gaseous Cr contaminants with the perovskite material LSCF (La$_{0.6}$Sr$_{0.4}$Co$_{0.2}$Fe$_{0.8}$O$_{3})$ commonly used as cathode for Solid Oxide Fuel Cells (SOFC) were investigated by means of X-ray absorption Spectroscopy (XAS) and Raman Spectroscopy. The setup consisted of a model cell with a GDC (Gd$_{0.1}$Ce$_{0.9}$O$_{2})$ electrolyte pellet with a LSCF cathode on both sides in a Cr containing sample holder. The chemical structure and valency of the precipitate were found to depend on the electrochemical conditions of the surface, particularly on the bias voltage and not the total current density present in the cell. Cr$^{6+}$ spinels were found to form under high bias voltage, while under low bias voltage mostly Cr$_{2}$O$_{3}$ was formed. The influence of the contact material (Au vs. Ag) and the effect of quenching were investigated by Raman Spectroscopy under operating conditions (800\r{ }C in air). XAS unlike EDS, XRD or XPS is a precise and valuable tool for the direct measurement of the oxidation state of transition metals in compounds if the concentration is low (contamination) and the substrate is porous. [Preview Abstract] |
Friday, October 1, 2010 4:10PM - 4:22PM |
C3.00010: Growth of tin sulfide thin films by pulsed laser deposition Jason Francis, Janet Tate Polycrystalline thin films of tin sulfide were grown on fused quartz substrates from an Sn$_{2}$S$_{3}$ target by pulsed laser deposition at temperatures ranging from 200C to 500C and pulse rates between 3Hz and 10Hz. 100nm thick films absorb roughly 50{\%} of incident light in the 400 to 700nm range, and have an optical band gap of approximately 1.5eV. Hall measurements give mobilities of 4 to 15cm$^{2}$/Vs, carrier concentrations of .25 to 2.5 x 10$^{16}$ cm$^{-3}$, and resistivities of 120 to 1000$\Omega $cm, depending on deposition conditions. These properties indicate that tin sulfide may be suitable for use as an absorber layer in thin film photovoltaic devices. [Preview Abstract] |
Friday, October 1, 2010 4:22PM - 4:34PM |
C3.00011: Magnetic Interaction Impact on Coercivity and Blocking Temperature in Co Nanoparticles Dongtao Zhang, You Qiang Magnetic nanoparticle interaction such as exchange and dipole interaction displays a rich variety of magnetic configurations resulting from competing energy terms. In this paper, we successfully prepared Co nanoparticles on Si (110) substrate with monodispersive particle size using an improved nanocluster deposition system. The particle film deposited on surface of Si wafer with different thickness from less than one cluster layer (non-interacting) through two cluster layers (weakly interaction) to a dense system of eight cluster layers (strongly interacting) were obtained by carefully adjusting the deposition time. There is an obvious magnetic interaction in the dense system, but it can be neglected in less than one layer sample for the large interparticle distance. Increase of the blocking temperature (TB) and coercivity with increasing of the film thickness is observed for the enhancing magnetic dipole interaction, and the TB is increased from 220 K to above room temperature. Also, the annealing study on the coercivity and blocking temperature found that high temperature quick annealing have a complex effect on the magnetic behavior. [Preview Abstract] |
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