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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 ...


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.


Structural Characterization Of Thin Film Photonic Crystals, G. Subramania, Rana Biswas, Kristen P. Constant, M. M. Sigalas, Kai-Ming Ho May 2001

Structural Characterization Of Thin Film Photonic Crystals, G. Subramania, Rana Biswas, Kristen P. Constant, M. M. Sigalas, Kai-Ming Ho

Materials Science and Engineering Publications

We quantitatively analyze the structure of thin film inverse-opal photonic crystals composed of ordered arrays of air pores in a background of titania. Ordering of the sphere template and introduction of the titania background were performed simultaneously in the thin film photonic crystals. Nondestructive optical measurements of backfilling with high refractive index liquids, angle-resolved reflectivity, and optical spectroscopy were combined with band-structure calculations. The analysis reveals a thin film photonic crystal structure with a very high filling fraction (92–94 %) of air and a substantial compression along the c axis (∼22–25%).


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.


Magnetic Force Microscopy Study Of Magnetization Reversal In Sputtered Fesial(N) Films, Chester C.H. Lo, J. E. Snyder, J. S. Leib, R. Chen, B. Kriegermeier-Sutton, Matthew J. Kramer, David C. Jiles, M. T. Kief Mar 2001

Magnetic Force Microscopy Study Of Magnetization Reversal In Sputtered Fesial(N) Films, Chester C.H. Lo, J. E. Snyder, J. S. Leib, R. Chen, B. Kriegermeier-Sutton, Matthew J. Kramer, David C. Jiles, M. T. Kief

Materials Science and Engineering Publications

The magnetization reversal in a series of rf-sputtered FeSiAl(N) films has been studied using magnetic force microscopy. A system has been developed which has the capability to image domain structure while an in-plane magnetic field is applied in situ. All films exhibited a stripe domain structure in zero applied field which was indicative of a perpendicular component of domain magnetization which alternates in sign. All films showed a similar sequence of magnetization processes: on reducing the applied field from saturation a fine stripe domain structure nucleated and then coarsened as the field was decreased to zero. Local switching of ...