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Full-Text Articles in Physics

Compositional Variation Of The Phonon Dispersion Curves Of Bcc Fe-Ga Alloys, Jerel L. Zarestky, V. O. Garlea, Thomas A. Lograsso, Deborah L. Schlagel, C. Stassis Nov 2005

Compositional Variation Of The Phonon Dispersion Curves Of Bcc Fe-Ga Alloys, Jerel L. Zarestky, V. O. Garlea, Thomas A. Lograsso, Deborah L. Schlagel, C. Stassis

Ames Laboratory Publications

Inelastic neutron scattering techniques have been used to measure the phonon dispersion curves of bcc Fe1−xGax (x=10.8, 13.3, 16.0, 22.5) alloys as a function of Ga concentration. The phonon frequencies of every branch were found to decrease significantly with increasing Ga concentration. The softening was most pronounced for the T2[ξξ0] branch and, to a lesser extent, the L[ξξξ] branch in the vicinity of ξ=2/3. The concentration dependence of the shear elastic constant C′=1∕2(C11−C12), calculated from the slope of the T ...


Fe–Ga/Pb(Mg1/3nb2/3)O3–Pbtio3 Magnetoelectric Laminate Composites, Shuxiang Dong, Junyi Zhai, Naigang Wang, Feiming Bai, Jiefang Li, D. Viehland, Thomas A. Lograsso Nov 2005

Fe–Ga/Pb(Mg1/3nb2/3)O3–Pbtio3 Magnetoelectric Laminate Composites, Shuxiang Dong, Junyi Zhai, Naigang Wang, Feiming Bai, Jiefang Li, D. Viehland, Thomas A. Lograsso

Ames Laboratory Publications

We have found large magnetoelectric (ME) effects in long-type laminate composites of Fe–20%Ga magnetostrictive alloys and piezoelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals. At lower frequencies, the ME voltage coefficient of a laminate with longitudinally magnetized and longitudinally polarized (i.e., L-L mode) layers was 1.41 V/Oe (or1.01 V/cm Oe). Near the natural resonant frequency ( ∼ 91 kHz) of the laminate, the ME voltage coefficients were found to be dramatically increased to 50.7 V/Oe (36.2 V/cm Oe)for the L-L mode. In ...


Magnetostructural Transition And Magnetocaloric Effect In Ni55mn20ga25 Single Crystals, M. Pasquale, C. P. Sasso, L. H. Lewis, L. Giudici, Thomas A. Lograsso, Deborah L. Schlagel Sep 2005

Magnetostructural Transition And Magnetocaloric Effect In Ni55mn20ga25 Single Crystals, M. Pasquale, C. P. Sasso, L. H. Lewis, L. Giudici, Thomas A. Lograsso, Deborah L. Schlagel

Ames Laboratory Publications

A first order transition from a paramagnetic-austenite phase to a ferromagnetic-martensite phase occurring in off-stoichiometry single crystals of Ni2MnGa at 313 K presents unique features due to the multifunctional character of the magnetic shape memory alloy. A remarkable magnetocaloric effect, associated with an entropy change up to ΔS≈−86 J kg−1 K−1 and an adiabatic temperature change ΔT≈2.2 K, accompanied by mechanical strain Δε⩾3% have been observed in samples subjected to changes of the applied magnetic field ΔH=4×106 A∕m (≈5 T). The effects of magnetic field, temperature, and stress on ...


Neutron Diffraction Studies Of The Magnetoelastic Compounds Tb5sixge4−X (X=2.2 And 2.5), V. O. Garlea, Jerel L. Zarestky, C. Y. Jones, L.-L. Lin, Deborah L. Schlagel, Thomas A. Lograsso, A. O. Tsokol, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., C. Stassis Sep 2005

Neutron Diffraction Studies Of The Magnetoelastic Compounds Tb5sixge4−X (X=2.2 And 2.5), V. O. Garlea, Jerel L. Zarestky, C. Y. Jones, L.-L. Lin, Deborah L. Schlagel, Thomas A. Lograsso, A. O. Tsokol, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., C. Stassis

Ames Laboratory Publications

We report the results of a neutron diffraction study, carried out on both single crystalline and polycrystalline samples of Tb5Si2.2Ge1.8 and polycrystalline Tb5Si2.5Ge1.5. On cooling, at approximately 120 K, the Tb5Si2.2Ge1.8 system undergoes a magnetoelastic transition from a high-temperature monoclinic-paramagnetic to a low-temperature orthorhombic-ferromagnetic structure. Between 120 K and 75 K, the magnetic structure has a net ferromagnetic component along the a axis direction. The moments are slightly canted with respect to the a axis, while the components along ...


Magnetic Force Microscopy Investigation Of Domain Structures In Fe–X At. % Ga Single Crystals (12, Feiming Bai, Jiefang Li, D. Viehland, D. Wu, Thomas A. Lograsso Jul 2005

Magnetic Force Microscopy Investigation Of Domain Structures In Fe–X At. % Ga Single Crystals (12, Feiming Bai, Jiefang Li, D. Viehland, D. Wu, Thomas A. Lograsso

Ames Laboratory Publications

The domain structure of furnace-cooled (FC) and post-annealed (PA) Fe–x at. % Ga (x = 12, 20, and 25) crystals has been investigated by magnetic force microscopy. For both FC and PA Fe–12 at. % Ga, the domains were found to be well-aligned and oriented along the [100] direction. For Fe–20 at. % Ga, although a preferred [100] orientation remained, a difference in morphology was found between FC and PA conditions—in the PA condition, clear dendritic domains were observed. For both FC and PA Fe–25 at. % Ga, a much reduced [100] preferred domain orientation was found, the domain size ...


Real-Space Observation Of Quasicrystalline Sn Monolayer Formed On The Fivefold Surface Of Icosahedral AlCuFe Quasicrystal, H. R. Sharma, M. Shimoda, A. R. Ross, Thomas A. Lograsso, A. P. Tsai Jul 2005

Real-Space Observation Of Quasicrystalline Sn Monolayer Formed On The Fivefold Surface Of Icosahedral AlCuFe Quasicrystal, H. R. Sharma, M. Shimoda, A. R. Ross, Thomas A. Lograsso, A. P. Tsai

Ames Laboratory Publications

We investigate a thin Sn film grown at elevated temperatures on the fivefold surface of an icosahedral AlCuFe quasicrystal by scanning tunneling microscopy (STM). At about one monolayer coverage, the deposited Sn is found to form a smooth film of height consistent with one-half of the lattice constant of the bulk Sn. Analysis based on the Fourier transform and autocorrelation function derived from high-resolution STM images reveals that Sn grows pseudomorphically and hence exhibits a quasicrystalline structure.


Hydrostatic Pressure Control Of The Magnetostructural Phase Transition In Gd5si2ge2 Single Crystals, C. Magen, L. Morellon, P. A. Algarabel, M. R. Ibarra, Z. Arnold, J. Kamarad, Thomas A. Lograsso, Deborah L. Schlagel, Vitalij K. Pecharsky, A. O. Tsokol, Karl A. Gschneidner Jr. Jul 2005

Hydrostatic Pressure Control Of The Magnetostructural Phase Transition In Gd5si2ge2 Single Crystals, C. Magen, L. Morellon, P. A. Algarabel, M. R. Ibarra, Z. Arnold, J. Kamarad, Thomas A. Lograsso, Deborah L. Schlagel, Vitalij K. Pecharsky, A. O. Tsokol, Karl A. Gschneidner Jr.

Ames Laboratory Publications

Magnetic and structural properties of single crystalline Gd5Si2Ge2 under hydrostatic pressure have been characterized by using magnetization, linear thermal expansion, and compressibility measurements. A strong dependence of Curie temperature on pressure, dTC∕dP=+4.8 K∕kbar, is observed in contrast with the smaller values of about 3 K∕kbar found in polycrystalline specimens. This difference reflects the role the microstructure may play in pressure-induced magnetic-crystallographic phase changes, likely related to stress relaxation at the grain boundaries, domain pinning and/or nucleation of defects. The pressure dependence of the critical magnetic field, d(dH ...


Copper Adsorption On The Fivefold Al70pd21mn9 Quasicrystal Surface, J. Ledieu, J. T. Hoeft, D. E. Reid, J. A. Smerdon, R. D. Diehl, N. Ferralis, Thomas A. Lograsso, A. R. Ross, R. Mcgrath Jul 2005

Copper Adsorption On The Fivefold Al70pd21mn9 Quasicrystal Surface, J. Ledieu, J. T. Hoeft, D. E. Reid, J. A. Smerdon, R. D. Diehl, N. Ferralis, Thomas A. Lograsso, A. R. Ross, R. Mcgrath

Ames Laboratory Publications

Recently we reported the formation of a quasiperiodic Cu thin film on the fivefold icosahedral Al-Pd-Mn quasicrystal using scanning tunneling microscopy, low energy electron diffraction, and Auger electron spectroscopy. Here we provide details pertaining to the growth, stability, and structure of this film. Structural information has been gained by LEED measurements carried out at 85 K. Cu atoms are organized periodically with a nearest-neighbor distance of 2.5±0.1 Å along the aperiodically spaced rows. Above 8 ML spontaneous mass transport resulting in island formation has been observed by STM. These observations point to ascending adatoms being responsible for ...


Magnetic Properties Of Single-Crystal Dyal2, A. L. Lima, A. O. Tsokol, Karl A. Gschneidner Jr., Vitalij K. Pecharsky, Thomas A. Lograsso, Deborah L. Schlagel Jul 2005

Magnetic Properties Of Single-Crystal Dyal2, A. L. Lima, A. O. Tsokol, Karl A. Gschneidner Jr., Vitalij K. Pecharsky, Thomas A. Lograsso, Deborah L. Schlagel

Ames Laboratory Publications

We measured the magnetic properties and heat capacity of three DyAl2 single crystals with the magnetic field oriented along the three principal crystallographic directions: [100], [110], and [111]. The isothermal entropy change versus temperature curves were obtained from heat capacity and magnetization data for these directions. The experimental results were successfully explained by a mean field model that includes spin reorientation, exchange interactions, and crystalline electric field effects. The anomalous magnetocaloric effect along the [111] direction predicted by theory was confirmed experimentally.


Magnetic Structure Of Gd5ge4, L. Tan, Andreas Kreyssig, J. W. Kim, Alan I. Goldman, Robert J. Mcqueeney, D. Wermeille, B. Sieve, Thomas A. Lograsso, Deborah L. Schlagel, Sergey L. Bud'ko, Vitalij K. Pecharsky, Karl A. Gschneidner Jr. Jun 2005

Magnetic Structure Of Gd5ge4, L. Tan, Andreas Kreyssig, J. W. Kim, Alan I. Goldman, Robert J. Mcqueeney, D. Wermeille, B. Sieve, Thomas A. Lograsso, Deborah L. Schlagel, Sergey L. Bud'ko, Vitalij K. Pecharsky, Karl A. Gschneidner Jr.

Ames Laboratory Publications

Gd5Ge4 crystallizes in the orthorhombic space group Pnma, and orders antiferromagnetically below the Néel temperatureTN∼127 K. We have employed x-ray resonant magnetic scattering to elucidate the details of the magnetic structure. The magnetic unit cell is the same as the chemical unit cell. From azimuth scans and the Q dependence of the magnetic scattering, all three Gd sites in the structure were determined to be in the same magnetic space group Pnm′a. The magnetic moments are primarily aligned along the c axis and the c components of the magnetic moments at the three different ...


Rheed And Stm Studies Of The Pseudo-Tenfold Surface Of The Ξ′-Al77.5pd19mn3.5 Approximant Crystal, H. R. Sharma, M. Shimoda, V. Fournée, Thomas A. Lograsso, A. P. Tsai Jun 2005

Rheed And Stm Studies Of The Pseudo-Tenfold Surface Of The Ξ′-Al77.5pd19mn3.5 Approximant Crystal, H. R. Sharma, M. Shimoda, V. Fournée, Thomas A. Lograsso, A. P. Tsai

Ames Laboratory Publications

The pseudo-tenfold surface of the ξ′-Al77.5Pd19Mn3.5 crystal, an approximant of the icosahedral Al–Pd–Mn quasicrystal, is investigated by reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy. The observed RHEED patterns of the surface after sputtering are found to be consistent with those of a simple cubic lattice with (11̅ 0) surface plane. The [001] and [110] axes of the surface plane are oriented along the principal low-index axes of the bulk. The RHEED patterns of the sputter-annealed surface consist of diffraction streaks with periodic spacings expected for the bulk truncated ...


Magnetic Field Dependence Of Galfenol Elastic Properties, G. Petculescu, K. B. Hathaway, Thomas A. Lograsso, M. Wun-Fogle, A. E. Clark May 2005

Magnetic Field Dependence Of Galfenol Elastic Properties, G. Petculescu, K. B. Hathaway, Thomas A. Lograsso, M. Wun-Fogle, A. E. Clark

Ames Laboratory Conference Papers, Posters, and Presentations

Elastic shear moduli measurements on Fe100−xGax (x = 12–33) single crystals (via resonant ultrasound spectroscopy) with and without a magnetic field and within 4–300 K are reported. The pronounced softening of the tetragonal shear modulus c′ is concluded to be, based on magnetoelastic coupling, the cause of the second peak in the tetragonal magnetostriction constant λ100 near x = 28. Exceedingly high ΔE effects ( ∼ 25%), combined with the extreme softness in c′ (c′<10 GPa), suggest structural changes take place, yet, gradual in nature, as the moduli show a smooth dependence on Ga concentration, temperature, and magnetic field. Shear anisotropy (c44/c′) as high as 14.7 was observed for Fe71.2Ga28.8.


Temperature Dependence Of The Magnetic Anisotropy And Magnetostriction Of Fe100−Xgax (X = 8.6, 16.6, 28.5), A. E. Clark, M. Wun-Fogle, J. B. Restorff, Kevin W. Dennis, Thomas A. Lograsso, R. William Mccallum May 2005

Temperature Dependence Of The Magnetic Anisotropy And Magnetostriction Of Fe100−Xgax (X = 8.6, 16.6, 28.5), A. E. Clark, M. Wun-Fogle, J. B. Restorff, Kevin W. Dennis, Thomas A. Lograsso, R. William Mccallum

Ames Laboratory Conference Papers, Posters, and Presentations

The temperature dependence of the lowest order magnetic anisotropy constant K1 and the lowest order saturation magnetostriction constant, (3/2)λ100, were measured from 4 K to 300 K for Fe91.4Ga8.6,Fe83.4Ga16.6, and Fe71.5Ga28.5 and were compared to the normalized magnetization power law, ml(l+1)/2. Fe91.4Ga8.6 maintains the magnetostriction anomaly of Fe (dλ100/dT>0) and K1 is a reasonable fit to the ml(l+1)/2power law with ...


Magnetic Anisotropy And Phase Transitions In Single-Crystal Tb5(Si2.2ge1.8), M. Han, J. E. Snyder, W. Tang, Thomas A. Lograsso, Deborah L. Schlagel, David C. Jiles May 2005

Magnetic Anisotropy And Phase Transitions In Single-Crystal Tb5(Si2.2ge1.8), M. Han, J. E. Snyder, W. Tang, Thomas A. Lograsso, Deborah L. Schlagel, David C. Jiles

Ames Laboratory Conference Papers, Posters, and Presentations

The Tb5(SixGe4−x) alloy system has many features in common with the Gd5(SixGe4−x)system although it has a more complex magnetic and structural phase diagram. This paper reports on the magnetic anisotropy and magnetic phase transition of single-crystalTb5(Si2.2Ge1.8) which has been investigated by the measurements of M-H and M-T along the a, b, and c axes. The variation of 1/χ vs T indicates that there is a transition from paramagnetic to ferromagnetic at Tc = 110 K. Below this ...


Thermal Expansion And Gruneisen Parameters In Some Pr–Ni–Si Compounds, S. H. Song, David C. Jiles, J. E. Snyder, A. O. Pecharsky, D. Wu, Kevin W. Dennis, Thomas A. Lograsso, R. William Mccallum May 2005

Thermal Expansion And Gruneisen Parameters In Some Pr–Ni–Si Compounds, S. H. Song, David C. Jiles, J. E. Snyder, A. O. Pecharsky, D. Wu, Kevin W. Dennis, Thomas A. Lograsso, R. William Mccallum

Ames Laboratory Conference Papers, Posters, and Presentations

In this study, the thermal expansion and Gruneisen parameter of polycrystalline “Pr5Ni2Si3” and “Pr15Ni7Si10” were investigated over the temperature range of 5–300 K. Calculations of the phonon contribution to thermal expansion were made, which allowed the magnetic contribution to thermal expansion to be calculated from the difference between the total thermal expansion and the phonon contribution. This resulted in a temperature-dependent magnetic contribution to thermal expansion that varied with the magnetic ordering of the material. The results show two magnetic transitions in each compound, the higher temperature transition corresponding ...


Magnetostrictive And Magnetoelectric Behavior Of Fe–20 At. % Ga/Pb(Zr,Ti)O3 Laminates, Shuxiang Dong, Junyi Zhai, Feiming Bai, Jiefang Li, D. Viehland, Thomas A. Lograsso Apr 2005

Magnetostrictive And Magnetoelectric Behavior Of Fe–20 At. % Ga/Pb(Zr,Ti)O3 Laminates, Shuxiang Dong, Junyi Zhai, Feiming Bai, Jiefang Li, D. Viehland, Thomas A. Lograsso

Ames Laboratory Publications

The magnetostrictive and magnetoelectric (ME) properties of laminate composites of Fe–20 at. % Ga and Pb(Zr,Ti)O3 (PZT) have been studied for laminates of different geometries. The results show that (i) a long-type magnetostrictive Fe–20 at. % Ga crystal plate oriented along 〈001〉c and magnetized in its longitudinal (or length) direction has higher magnetostriction than a disk-type one; and consequently (ii) a long-type Fe–20 at. % Ga/PZT laminate has a giant ME effect, and is sensitive to low-level magnetic fields.


Corrosion Of Steel By Lead Bismuth Eutectic, John Farley, Allen L. Johnson, Dale L. Perry Jan 2005

Corrosion Of Steel By Lead Bismuth Eutectic, John Farley, Allen L. Johnson, Dale L. Perry

Transmutation Sciences Materials (TRP)

There is an active international interest in lead-bismuth eutectic and similar liquid lead systems because of the relevance to the transmutation of nuclear waste, fast reactors, and spallation neutron sources.

Materials in these systems must be able to tolerate high neutron fluxes, high temperatures, and chemical corrosion. For lead bismuth eutectic (LBE) systems, there is an additional challenge because the corrosive behaviors of materials in LBE are not well understood. Most of the available information on LBE systems has come from the Russians, who have over 80 reactor-years experience with LBE coolant in their Alpha-class submarine reactors. The Russians found ...