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Joan Shea
Kyungsu Na, Changbum Jo, Jeongnam Kim, Kanghee Cho, Jinhwan Jung, Yongbeom Seo, Bradley F. Chmelka, and Ryong Ryoo
V.I. Valtchinov, V. Gelev, Y. Dagon J. Bock, I.S. Kohane, A. Usheva
A. Usheva
Also: George L. Athens, Jan D. Epping, Sylvian Cadars, Yair Ein-Eli
Also Seth Gleiman
Conference Proceedings
Max C. Watson, Evgeni S. Penev, and Frank L. H. Brown
UCSB Author: Bazan, GC
Co-author: Guillermo Bazanl. The paper is all available through http://dx.doi.org
UCSB Author: Nguyen, Thuc-Quyen
Need specific date of publication and volume, etc.
Bulk specimens of the hetaerolite solid solution ZnxMn3-xO4, with x = 0, 0.25, 0.5, 0.75, and 1 have been prepared as homogeneous, phase-pure polycrystalline samples as ascertained by neutron diffraction measurements. Samples with x = 0.25, 0.5, and 0.75 exhibit shifted magnetic hysteresis loops at low temperature, characteristic of exchange bias typically seen in magnetic composites. We propose that the unusual magnetic behavior arises as a result of a nanoscale mixture of ferrimagnetic and antiferromagnetic regions that are distinct but lack long-range order. While some glassy behavior is seen in AC magnetic measurements, its magnitude is not sufficient to account for the observed dramatic exchange bias. Furthermore, isothermal and thermoremanent magnetization measurements distinguish this material from a pure spin glass. The title system offers insights into the alloying of a ferrimagnet Mn3O4 with an antiferromagnet ZnMn2O4 wherein distinct magnetic clusters grow and percolate to produce a smooth transition between competing orders.
2009 Student Symposium
At first sight, the quenched tetragonal spinel CuMn2O4 can be formulated with Cu2+ and Mn3+, implying that the tetrahedral site is Jahn−Teller (JT)-active Cu2+and the octahedral site is JT-active Mn3+. High-resolution, high-momentum-transfer neutron scattering analysis suggests that the sample has 30% inversion: Mn on the tetrahedral Cu site with compensating Cu on the octahedral site. Reverse Monte Carlo (RMC) analysis of the pair distribution function allows details of metal−oxygen connectivity to be probed in a manner that is significantly on the local rather than the average scale. Bond valence analysis of the RMC supercell reveals that both JT ions disproportionate to higher and lower valence states as a means of avoiding their JT tendency, particularly on the tetrahedral site. The occurrence of Cu3+ in particular is suggested for the first time and is supported by X-ray photoelectron spectroscopy data. The bimodal distribution of O−Cu−O bond angles at the tetrahedral site (distinct from what is seen for O−Mn−O bond angles) further reveals a hidden distinction between sites previously considered to be equivalent. Application of total scattering techniques originally developed for highly disordered materials permits the examination of nanoscale crystalline structure with elemental specificity that is not available in traditional reciprocal-space analysis.
Los Alamos Materials Strategy
The past decade has seen researchers develop and apply novel technologies for biomolecular detection, at times approaching hard limits imposed by physics and chemistry. In nearly all sensors, the transport of target molecules to the sensor can play as critical a role as the chemical reaction itself in governing binding kinetics, and ultimately performance. Yet rarely does an analysis of the interplay between diffusion, convection and reaction motivate experimental design or interpretation. Here we develop a physically intuitive and practical understanding of analyte transport for researchers who develop and employ biosensors based on surface capture. We explore the qualitatively distinct behaviors that result, develop rules of thumb to quickly determine how a given system will behave, and derive order-of-magnitude estimates for fundamental quantities of interest, such as fluxes, collection rates and equilibration times. We pay particular attention to collection limits for micro- and nanoscale sensors, and highlight unexplained discrepancies between reported values and theoretical limits
Self-consistent field theory is used to study the self-assembly of a triblock copolymer melt. Two different external factors (temperature and solvent) are shown to affect the self-assembly. Either one or two-step self-assembly can be found as a function of temperature in the case of a neat triblock melt, or as a function of increasing solvent content (for non-selective solvents) in the case of a triblock-solvent mixture. For selective solvents, it is shown that increasing the solvent content leads to more complicated self-assembly mechanisms, including a reversed transition where order is found to increase instead of decreasing as expected, and re-entrant behavior where order is found to increase at first, and then decrease to a previous state of disorder.
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