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Anisotropy of conduction electrons in n-InSb and extrinsic and intrinsic properties of HgCdTe

Description: The anistropy of the orbital and spin properties of conduction electrons in InSb has been measured simultaneously using a cyclotron-resonance type experiment. This represents the first time that the anistropy of effective mass in InSb has been directly measured using an optical method.
Date: August 1991
Creator: Yoon, Im T. (Im Taek)
Partner: UNT Libraries

Anisotropies in the cosmic microwave background: Theory

Description: Anisotropies in the Cosmic Microwave Background (CMB) contain a wealth of information about the past history of the universe and the present values of cosmological parameters. I online some of the theoretical advances of the last few years. In particular, I emphasize that for a wide class of cosmological models, theorists can accurately calculate the spectrum to better than a percent. The spectrum of anisotropies today is directly related to the pattern of inhomogeneities present at the time of recombination. This recognition leads to a powerful argument that will enable us to distinguish inflationary models from other models of structure formation. If the inflationary models turn out to be correct, the free parameters in these models will be determined to unprecedented accuracy by the upcoming satellite missions.
Date: February 1, 1998
Creator: Dodelson, S.
Partner: UNT Libraries Government Documents Department

Explicit Determination of Piezoelectric Eshelby Tensors for a Spheroidal Inclusion

Description: In this paper, by systematically treating the integrals involved in the piezoelectric inclusion problem, explicit results were obtained for the piezoelectric Eshelby tensors for a spheroidal inclusion aligned along the axis of the anisotropy in a transversely isotropic piezoelectric material. This problem was first treated by Dunn and Wienecke (1996) using a Green's function approach, which closely follows Withers' approach (1989) for an ellipsoidal inclusion problem in a transversely isotropic elastic medium. The same problem was recently treated by Michelitsch and Levin (2000) also using a Green's function approach. In this paper, a different method was used to obtain the explicit results for the piezoelectric Eshelby tensors for a spheroidal inclusion. The method is a direct extension of a more unified approach, which has been recently developed by Mikata (2000), which is based on Deeg's results (1980) on a piezoelectric inclusion problem. The main advantage of this method is that it is more straightforward and simpler than Dunn and Wienecke (1996), or Michelitsch and Levin (2000), and the results are a little bit more explicit than their solutions. The key step of this paper is an analytical closed form evaluation of several integrals, which was made possible after a careful treatment of a certain bi-cubic equation.
Date: June 21, 2001
Creator: Mikata, Yozo
Partner: UNT Libraries Government Documents Department

Field driven ferromagnetic phase nucleation and propagation from the domain boundaries in antiferromagnetically coupled perpendicular anisotropy films

Description: We investigate the reversal process in antiferromagnetically coupled [Co/Pt]{sub X-1}/{l_brace}Co/Ru/[Co/Pt]{sub X-1}{r_brace}{sub 16} multilayer films by combining magnetometry and Magnetic soft X-ray Transmission Microscopy (MXTM). After out-of-plane demagnetization, a stable one dimensional ferromagnetic (FM) stripe domain phase (tiger-tail phase) for a thick stack sample (X=7 is obtained), while metastable sharp antiferromagnetic (AF) domain walls are observed in the remanent state for a thinner stack sample (X=6). When applying an external magnetic field the sharp domain walls of the thinner stack sample transform at a certain threshold field into the FM stripe domain wall phase. We present magnetic energy calculations that reveal the underlying energetics driving the overall reversal mechanisms.
Date: December 9, 2008
Creator: Hauet, Thomas; Gunther, Christian M.; Hovorka, Ondrej; Berger, Andreas; Im, Mi-Young; Fischer, Peter et al.
Partner: UNT Libraries Government Documents Department

Friction Anisotropy: A unique and intrinsic property of decagonal quasicrystals

Description: We show that friction anisotropy is an intrinsic property of the atomic structure of Al-Ni-Co decagonal quasicrystals and not only of clean and well-ordered surfaces that can be prepared in vacuum [J.Y. Park et al., Science (2005)]. Friction anisotropy is manifested both in nanometer size contacts obtained with sharp atomic force microscope (AFM) tips as well as in macroscopic contacts produced in pin-on-disc tribometers. We show that the friction anisotropy, which is not observed when an amorphous oxide film covers the surface, is recovered when the film is removed due to wear. Equally important is the loss of the friction anisotropy when the quasicrystalline order is destroyed due to cumulative wear. These results reveal the intimate connection between the mechanical properties of these materials and their peculiar atomic structure.
Date: June 25, 2008
Creator: Mulleregan, Alice; Park, Jeong Young; Salmeron, Miquel; Ogetree, D.F.; Jenks, C.J.; Thiel, P.A. et al.
Partner: UNT Libraries Government Documents Department

Aligned vertical fractures, HTI reservoir symmetry, and Thomsenseismic anisotropy parameters for polar media

Description: Sayers and Kachanov (1991) defined crack-influence parameters that are shown to be directly related to Thomsen (1986) weak-anisotropy seismic parameters for fractured reservoirs when the crack/fracture density is small enough. These results are then applied to the problem of seismic wave propagation in polar (i.e., non-isotropic) reservoirs having HTI seismic wave symmetry due to the presence of aligned vertical fractures and resulting in azimuthal seismic wave symmetry at the earth's surface. The approach presented suggests one method of inverting for fracture density from wave-speed data. It is also observed that the angular location {theta}{sub ex} of the extreme value (peak or trough) of the quasi-SV-wave speed for VTI occurs at an angle determined approximately by the formula tan{sup 2} {theta}{sub ex} {approx_equal} tan {theta}{sub m} = [(c{sub 33} - c{sub 44})/(c{sub 11}-c{sub 44})]{sup 1/2}, where {theta}{sub m} is an angle determined directly (as shown) from the c{sub ij} elastic stiffnesses, whenever these are known from either quasi-static or seismic wave measurements. Alternatively, {theta}{sub ex} is given in terms of the Thomsen seismic anisotropy parameters by tan {theta}{sub ex} {approx_equal} ([v{sub p}{sup 2}(0)-v{sub s}{sup 2}(0)]/[(1 + 2{epsilon})v{sub p}{sup 2}(0)-v{sub s}{sup 2}(0)]){sup 1/4}, where {epsilon} = (c{sub 11}-c{sub 33})/2c{sub 33}, v{sub p}{sup 2}(0) = c{sub 33}/{rho}, and v{sub s}{sup 2}(0) = c{sub 44}/{rho}, with {rho} being the background inertial mass density. The axis of symmetry is always treated here as the x{sub 3}-axis for either VTI symmetry (due, for example, to horizontal cracks), or HTI symmetry (due to aligned vertical cracks). Then the meaning of the stiffnesses is derived from the fracture analysis in the same way for VTI and HTI media, but for HTI the wave speeds relative to the earth's surface are shifted by 90{sup o} in the plane perpendicular to the aligned vertical fractures. Skempton's (1954) coefficient is used ...
Date: December 12, 2007
Creator: Berryman, James G.
Partner: UNT Libraries Government Documents Department

Microstructural Evolution Based on Fundamental Interfacial Properties

Description: This first CMSN project has been operating since the summer of 1999. The main achievement of the project was to bring together a community of materials scientists, physicists and mathematicians who share a common interest in the properties of interfaces and the impact of those properties on microstructural evolution. Six full workshops were held at Carnegie Mellon (CMU), Northwestern (NWU), Santa Fe, Northeastern University (NEU), National Institute for Standards and Technology (NIST), Ames Laboratory, and at the University of California in San Diego (UCSD) respectively. Substantial scientific results were obtained through the sustained contact between the members of the project. A recent issue of Interface Science (volume 10, issue 2/3, July 2002) was dedicated to the output of the project. The results include: the development of methods for extracting anisotropic boundary energy and mobility from molecular dynamics simulations of solid/liquid interfaces in nickel; the extraction of anisotropic energies and mobilities in aluminum from similar MD simulations; the application of parallel computation to the calculation of interfacial properties; the development of a method to extract interfacial properties from the fluctuations in interface position through consideration of interfacial stiffness; the use of anisotropic interface properties in studies of abnormal grain growth; the discovery of abnormal grain growth from random distributions of orientation in subgrain networks; the direct comparison at the scale of individual grains between experimentally observed grain growth and simulations, which confirmed the importance of including anisotropic interfacial properties in the simulations; the classification of a rich variety of dendritic morphologies based on slight variations in the anisotropy of the solid-liquid interface; development of phase field methods that permit both solidification and grain growth to be simulated within the same framework.
Date: July 11, 2003
Creator: Rollett, A. D.; Srolovitz, D. J. & Karma, A.
Partner: UNT Libraries Government Documents Department

Direct Observation of Field and Temperature Induced Domain Replication in Dipolar Coupled Perpendicular Anisotropy Films

Description: Dipolar interactions in a soft/Pd/hard [CoNi/Pd]{sub 30}/Pd/[Co/Pd]{sub 20} multilayer system, where a thick Pd layer between two ferromagnetic units prevents direct exchange coupling, are directly revealed by combining magnetometry and state-of-the-art layer resolving soft x-ray imaging techniques with sub-100-nm spatial resolution. The domains forming in the soft layer during external magnetic field reversal are found to match the domains previously trapped in the hard layer. The low Curie temperature of the soft layer allows varying its intrinsic parameters via temperature and thus studying the competition with dipolar fields due to the domains in the hard layer. Micromagnetic simulations elucidate the role of [CoNi/Pd] magnetization, exchange, and anisotropy in the duplication process. Finally, thermally driven domain replication in remanence during temperature cycling is demonstrated.
Date: July 1, 2007
Creator: Hauet, T.; Gunther, C.M.; Pfau, B.; Eisebitt, S.; Fischer, P.; Rick, R. L. et al.
Partner: UNT Libraries Government Documents Department

Visualization of microcrack anisotropy in granite affected by afault zone, using confocal laser scanning microscope

Description: Brittle deformation in granite can generate a fracture system with different patterns. Detailed fracture analyses at both macroscopic and microscopic scales, together with physical property data from a drill-core, are used to classify the effects of reverse fault deformation in four domains: (1) undeformed granite, (2) fractured granite with cataclastic seams, (3) fractured granite from the damage zone, and (4) foliated cataclasite from the core of the fault. Intact samples from two orthogonal directions, horizontal (H) and vertical (V), from the four domains indicate a developing fracture anisotropy toward the fault, which is highly developed in the damage zone. As a specific illustration of this phenomenon, resin impregnation, using a confocal laser scanning microscope (CLSM) technique is applied to visualize the fracture anisotropy developed in the Toki Granite, Japan. As a result, microcrack networks have been observed to develop in H sections and elongate open cracks in V sections, suggesting that flow pathways can be determined by deformation.
Date: January 2, 2004
Creator: Onishi, Celia T. & Shimizu, Ichiko
Partner: UNT Libraries Government Documents Department

Role of magnetic anisotropy in spin-filter junctions

Description: We have fabricated oxide-based spin-filter junctions in which we demonstrate that magnetic anisotropy can be used to tune the transport behavior of spin-filter junctions. We have demonstrated spin-filtering behavior in La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/CoCr{sub 2}O{sub 4}/Fe{sub 3}O{sub 4} and La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/MnCr{sub 2}O{sub 4}/Fe{sub 3}O{sub 4} junctions where the interface anisotropy plays a significant role in determining transport behavior. Detailed studies of chemical and magnetic structure at the interfaces indicate that abrupt changes in magnetic anisotropy across the nonisostructural interface is the cause of the significant suppression of junction magnetoresistance in junctions with MnCr{sub 2}O{sub 4} barrier layers.
Date: January 10, 2011
Creator: Chopdekar, R.V.; Wong, F.; Nelson-Cheeseman, B.B.; Liberati, M.; Arenholz, E. & Suzuki, Y.
Partner: UNT Libraries Government Documents Department

Electronic and magnetic structure of GaxFe1-x thin films

Description: The electronic as well as magnetic properties of Ga{sub x}Fe{sub 1-x} films were studied by soft x-ray measurements. Using x-ray magnetic circular dichroism the Fe majority-spin band was found to be completely filled for x {approx} 0.3. With further enhanced Ga content, the Fe moment as well as the angular dependence of the x-ray magnetic linear dichroism decrease strongly, which we attribute to the formation of D0{sub 3} precipitates. Moreover, the magnetocrystalline anisotropy drops significantly.
Date: September 8, 2010
Creator: Arenholz, E.; van der Laan, G.; McClure, A. & Idzerda, Y.
Partner: UNT Libraries Government Documents Department

Aligned vertical fractures, HTI reservoir symmetry, and Thomsenseismic anisotropy parameters

Description: The Sayers and Kachanov (1991) crack-influence parametersare shown to be directly related to Thomsen (1986) weak-anisotropyseismic parameters for fractured reservoirs when the crack density issmall enough. These results are then applied to seismic wave propagationin reservoirs having HTI symmetry due to aligned vertical fractures. Theapproach suggests a method of inverting for fracture density from wavespeed data.
Date: June 27, 2007
Creator: Berryman, James G.
Partner: UNT Libraries Government Documents Department

Surface structure of CdSe Nanorods revealed by combined X-rayabsorption fine structure measurements and ab-initio calculations

Description: We report orientation-specific, surface-sensitive structural characterization of colloidal CdSe nanorods with extended X-ray absorption fine structure spectroscopy and ab-initio density functional theory calculations. Our measurements of crystallographically-aligned CdSe nanorods show that they have reconstructed Cd-rich surfaces. They exhibit orientation-dependent changes in interatomic distances which are qualitatively reproduced by our calculations. These calculations reveal that the measured interatomic distance anisotropy originates from the nanorod surface.
Date: January 27, 2006
Creator: Aruguete, Deborah A.; Marcus, Matthew A.; Li, Liang-shi; Williamson, Andrew; Fakra, Sirine; Gygi, Francois et al.
Partner: UNT Libraries Government Documents Department


Description: Both the magnitude and alignment of the transferred angular momentum in the reaction {sup 165}Ho + {sup 165}Ho have been measured as a function of Q value via continuum {gamma}-ray multiplicity and anisotropy techniques. Two regimes are observed: A low-Q-value regime where the aligned angular momentum component dominates over the random components, and a large-Q-value regime where the random components dominate and decrease the spin alignment.
Date: July 1, 1980
Creator: Wozniak, G.J.; McDonald, R.J.; Pacheco, A.J.; Hsu, C.C.; Morrissey, D.J.; Sobotka, L.G. et al.
Partner: UNT Libraries Government Documents Department

Vadose Zone Transport Field Study: FY 2002 Status Report

Description: This work reported here is part of the U. S. Department of Energy’s Science and Technology Initiative to develop improved conceptual models of flow and transport in the vadose zone, particularly for the Hanford Site, Washington. The National Academy of Sciences has identified significant knowledge gaps in conceptual model development as one reason for discovery of subsurface contamination in unexpected places. Inadequate conceptualizations limits, not only the understanding of long-term fate and transport, but also the selection and design of remediation technologies. Current conceptual models are limited partly because they do not account for the random heterogeneity that occurs under the extremes of very nonlinear flow behavior typical of the Hanford vadose zone. A major improvement in conceptual modeling of the Hanford vadose zone includes a better understanding and description of soil anisotropy, a property that appears to control much of the subsurface flow and transport in layered sediments at the Hanford Site.
Date: January 2, 2003
Creator: Ward, Anderson L.; Gee, Glendon W.; Zhang, Z. F. & Keller, Jason M.
Partner: UNT Libraries Government Documents Department

Multi-Regional Reactive Transport Due to Strong Anisotropy in Unsaturated Soils with Evolving Scales of Heterogeneity

Description: Anisotropic and heterogeneous flow in unsaturated porous media is dependent on saturation conditions, and currently there exist limited options that adequately model this phenomenon. The phenomenon of lateral spreading commonly attributed to anisotropy can move contaminants beyond compliance boundaries at unexpected velocitites essentially bypassing large regions of the subsurface.
Date: October 13, 2006
Creator: Mo, Xinghua
Partner: UNT Libraries Government Documents Department

Transport anisotropy as a probe of the interstitial vortex state in superconductors with artificial pinning arrays

Description: We show using simulations that when interstitial vortices are present in superconductors with periodic pinning arrays, the transport in two perpendicular directions can be anisotropic. The degree of the anisotropy varies as a function of field due to the fact that the interstitial vortex lattice has distinct orderings at different matching fields. The anisotropy is most pronounced at the matching fields but persists at incommensurate fields, and it is most prominent for triangular, honeycomb, and kagome pinning arrays. Square pinning arrays can also show anisotropic transport at certain fields in spite of the fact that the perpendicular directions of the square pinning array are identical. We show that the anisotropy results from distinct vortex dynamical states and that although the critical depinning force may be lower in one direction, the vortex velocity above depinning may also be lower in the same direction for ranges of external drives where both directions are depinned. For honeycomb and kagome pinning arrays, the anisotropy can show multiple reversals as a function of field. We argue that when the pinning sites can be multiply occupied such that no interstitial vortices are present, the anisotropy is strongly reduced or absent.
Date: January 1, 2008
Creator: Reichhardt, Charles & Reichhardt, Cynthia
Partner: UNT Libraries Government Documents Department

Correlation between Crystallographic and Magnetic Domains at Co/NiO(001) Interfaces

Description: Using soft x-ray spectromicroscopy we show that NiO(001) exhibits a crystallographic and magnetic domain structure near the surface identical to that of the bulk. Upon Co deposition a perpendicular coupling between the Ni and Co moments is observed that persists even after formation of uncompensated Ni spins at the interface through annealing. The chemical composition at the interface alters its crystallographic structure and leads to a reorientation of the Ni moments from the <112> to the <110> direction. We show that this reorientation is driven by changes in the magnetocrystalline anisotropy rather than exchange coupling mediated by residual uncompensated spins.
Date: December 18, 2008
Creator: Ohldag, H.; van der Laan, G. & Arenholz, E.
Partner: UNT Libraries Government Documents Department

Ni spin switching induced by magnetic frustration in FeMn/Ni/Cu(001)

Description: Epitaxially grown FeMn/Ni/Cu(001) films are investigated by Photoemission Electron Microscopy and Magneto-Optic Kerr Effect. We find that as the FeMn overlayer changes from paramagnetic to antiferromagnetic state, it could switch the ferromagnetic Ni spin direction from out-of-plane to in-plane direction of the film. This phenomenon reveals a new mechanism of creating magnetic anisotropy and is attributed to the out-of-plane spin frustration at the FeMn-Ni interface.
Date: March 8, 2009
Creator: Wu, J.; Choi, J.; Scholl, A.; Doran, A.; Arenholz, E.; Hwang, Chanyong et al.
Partner: UNT Libraries Government Documents Department