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Full-Text Articles in Physics

Absence Of Fine Structure In The Photoemission Spectrum Of The Icosahedral Al-Pd-Mn Quasicrystal, Z. M. Stadnik, D. Purdie, Y. Baer, Thomas A. Lograsso Nov 2001

Absence Of Fine Structure In The Photoemission Spectrum Of The Icosahedral Al-Pd-Mn Quasicrystal, Z. M. Stadnik, D. Purdie, Y. Baer, Thomas A. Lograsso

Ames Laboratory Publications

The results of the low-temperature ultrahigh-energy-resolution photoemission studies of a single-grain icosahedral alloy Al70Pd21.5Mn8.5 have been presented. The existence of the theoretically predicted pseudogap in the density of states at the Fermi energy has been confirmed. No evidence of the theoretically predicted spikiness of the density of states could be observed. It has been suggested that the failure to detect the predicted spikiness of the density of states in icosahedral quasicrystals is consistent with the results of Zijlstra and Janssen [Europhys. Lett. 52, 578 (2000)] who showed that the spikiness occurs only in ...


Superconducting Mgb2 Thin Films By Pulsed Laser Deposition, S. R. Shinde, S. B. Ogale, R. L. Greene, T. Venkatesan, Paul C. Canfield, Sergey L. Bud'ko, G. Lapertot, Cedomir Petrovic Jul 2001

Superconducting Mgb2 Thin Films By Pulsed Laser Deposition, S. R. Shinde, S. B. Ogale, R. L. Greene, T. Venkatesan, Paul C. Canfield, Sergey L. Bud'ko, G. Lapertot, Cedomir Petrovic

Ames Laboratory Publications

Growth of MgB2thin films by pulsed laser deposition is examined under ex situ and in situprocessing conditions. For the ex situ process, boronfilmsgrown by pulsed laser deposition were annealed at 900 °C with excess Mg. For the in situ process, different approaches involving ablation from a stoichiometric target under different growth conditions, as well as multilayer deposition involving interposed Mg layers were examined and analyzed. Magnetic measurements on ex situ processed films show Tc of ∼39 K, while the current best in situfilms show a susceptibility transition at ∼22 K.


Microwave Properties Of Superconducting Mgb2, N. Hakim, P. V. Parimi, C. Kusko, S. Sridhar, Paul C. Canfield, Sergey L. Bud'ko, Douglas K. Finnemore Jun 2001

Microwave Properties Of Superconducting Mgb2, N. Hakim, P. V. Parimi, C. Kusko, S. Sridhar, Paul C. Canfield, Sergey L. Bud'ko, Douglas K. Finnemore

Ames Laboratory Publications

Measurements of 10 GHz microwavesurface resistance, Rs, of dense MgB2wire and pellet are reported. Significant improvements are observed in the wire with reduction of porosity. The data lie substantially above the theoretical estimates for a pure Bardeen–Cooper–Schrieffer s-wave superconductor. However, the Rs (20 K) of the wire is an order of magnitude lower than that of polycrystalYBa2Cu3O6.95 and matches with single-crystal YBa2Cu3O6.95. The results show promise for the use of MgB2 in microwave applications.


Phonon Softening In Ni-Mn-Ga Alloys, Lluís Mañosa, Antoni Planes, Jerel L. Zarestky, Thomas A. Lograsso, Deborah L. Schlagel, C. Stassis Jun 2001

Phonon Softening In Ni-Mn-Ga Alloys, Lluís Mañosa, Antoni Planes, Jerel L. Zarestky, Thomas A. Lograsso, Deborah L. Schlagel, C. Stassis

Ames Laboratory Publications

The TA2 phonon dispersion curves of Ni-Mn-Ga alloys with different compositions which transform to different martensitic structures have been measured over a broad temperature range covering both paramagnetic and ferromagnetic phases. The branches show an anomaly (dip) at a wave number that depends on the particular martensitic structure, and there is softening of these anomalous phonons with decreasing temperature. This softening is enhanced below the Curie point, as a consequence of spin-phonon coupling. This effect is stronger for systems with higher electronic concentration.


Physical Properties Of Heusler-Like Fe2val, Ye Feng, J. Y. Rhee, T. A. Wiener, David W. Lynch, B. E. Hubbard, A. J. Sievers, Deborah L. Schlagel, Thomas A. Lograsso, L. L. Miller Apr 2001

Physical Properties Of Heusler-Like Fe2val, Ye Feng, J. Y. Rhee, T. A. Wiener, David W. Lynch, B. E. Hubbard, A. J. Sievers, Deborah L. Schlagel, Thomas A. Lograsso, L. L. Miller

Ames Laboratory Publications

A comprehensive characterization of the compound Fe2VAl was carried out. Samples grown by arc melting or the Bridgman method have Al and Fe deficiencies of up to 5 at. %. Czochralski-grown samples were Fe rich and Al deficient. X-ray diffraction implies appreciable antisite disorder in all of our samples. Fourier-transform infrared (FTIR) spectroscopy measurements showed that the carrier density and scattering time had little sample-to-sample variation or temperature dependence for near-stoichiometric samples. FTIR and dc resistivity suggest that the transport properties of Fe2VAl are influenced by both localized and delocalized carriers, with the former primarily responsible for ...


Composite Magnetostrictive Materials For Advanced Automotive Magnetomechanical Sensors, R. William Mccallum, Kevin W. Dennis, David C. Jiles, John E. Snyder, Y. H. Chen Apr 2001

Composite Magnetostrictive Materials For Advanced Automotive Magnetomechanical Sensors, R. William Mccallum, Kevin W. Dennis, David C. Jiles, John E. Snyder, Y. H. Chen

Ames Laboratory Publications

In this paper we present the development of a composite magnetostrictive material for automotive applications. The material is based on cobaltferrite,CoO⋅Fe2O3, and contains a small fraction of metallic matrix phase that serves both as a liquid-phasesintering aid during processing and enhances the mechanical properties over those of a simple sinteredferrite ceramic. In addition the metal matrix makes it possible to braze the material, making the assembly of a sensor relatively simple. The material exhibits good sensitivity and should have high corrosion resistance, while at the same time it is low in cost.