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Full-Text Articles in Physics

Magnetic Domains In Magnetostrictive Fe–Ga Alloys, Qingfeng Xing, Thomas A. Lograsso Nov 2008

Magnetic Domains In Magnetostrictive Fe–Ga Alloys, Qingfeng Xing, Thomas A. Lograsso

Ames Laboratory Publications

Lorentz microscopy was applied to the observation of magnetic domains in iron-gallium (Fe–Ga) alloys. Results did not show any link between the magnetic domains and the magnetostriction enhancement by Ga addition, but did reveal that the drastic decrease in magnetostriction for Fe–31.2 at. % Ga was due to the presence of large scale precipitates. Magnetic domain features did not change in the alloys of A2, D03, A2+D03,A2+B2+D03, and A2+fine scale precipitates. Large scale precipitates within the slow-cooled Fe–31.2 at. % Ga affected both the distribution and wall motion of ...


Growth Of Bi Thin Films On Quasicrystal Surfaces, H. R. Sharma, V. Fournée, M. Shimoda, A. R. Ross, Thomas A. Lograsso, P. Gille, A. P. Tsai Oct 2008

Growth Of Bi Thin Films On Quasicrystal Surfaces, H. R. Sharma, V. Fournée, M. Shimoda, A. R. Ross, Thomas A. Lograsso, P. Gille, A. P. Tsai

Ames Laboratory Publications

We present a comprehensive study of Bi thin-film growth on quasicrystal surfaces. The substrates used for the growth are the fivefold surface of icosahedral (i)-Al-Cu-Fe and i-Al-Pd-Mn and the tenfold surface of decagonal (d)-Al-Ni-Co quasicrystals. The growth is investigated at 300 and 525 K substrate temperatures and at different coverage (θ) ranging from submonolayer to ten monolayers. The film is characterized by scanning tunneling microscopy, reflection high-energy electron diffraction, and x-ray photoelectron spectroscopy. At 300 K, the deposited Bi yields a quasicrystalline film for θ≤1. For 1<θ<5, it forms nanocrystallites with (100) surface orientation. The islands have magic heights, which correspond to the stacking of four atomic layers (predominantly). The selection of magic heights is interpreted in terms of quantum size effects arising from the electron confinement within the film thickness. The islands establish rotational epitaxial relationship with the substrate. For higher coverage, the film grows with monatomic height, not with magic heights, and reflects the symmetry of the bulk Bi. When deposition is performed at 525 K, terrace diffusion is more effective, resulting in the aggregation of Bi adatoms developing into a smooth monolayer with quasiperiodic order. At this temperature, multilayers do not adsorb.


Magnetic Structure Of Dy3+ In Hexagonal Multiferroic Dymno3, Shibabrata Nandi, Andreas Kreyssig, J.-Q. Yan, Matthew D. Vannette, J. C. Lang, L. Tan, J. W. Kim, Ruslan Prozorov, Thomas A. Lograsso, Robert J. Mcqueeney, Alan I. Goldman Aug 2008

Magnetic Structure Of Dy3+ In Hexagonal Multiferroic Dymno3, Shibabrata Nandi, Andreas Kreyssig, J.-Q. Yan, Matthew D. Vannette, J. C. Lang, L. Tan, J. W. Kim, Ruslan Prozorov, Thomas A. Lograsso, Robert J. Mcqueeney, Alan I. Goldman

Ames Laboratory Publications

Element specific x-ray resonant magnetic scattering (XRMS) investigations were undertaken to determine the magnetic structure of the multiferroic compound, hexagonal DyMnO3. In the temperature range from 68 K down to 8 K the Dy3+ moments are aligned and antiferromagnetically correlated in the c direction according to the magnetic representation Γ3. The temperature dependence of the observed intensity can be modeled assuming the splitting of ground-state doublet crystal-field levels of Dy3+ by the exchange field of Mn3+. XRMS together with magnetization measurements indicate that the magnetic representation is Γ2 below 8 K.


Nucleation And Growth Of A Quasicrystalline Monolayer: Bi Adsorption On The Fivefold Surface Of I-Al70pd21mn9, J. A. Smerdon, J. K. Parle, L. H. Wearing, Thomas A. Lograsso, A. R. Ross, R. Mcgrath Aug 2008

Nucleation And Growth Of A Quasicrystalline Monolayer: Bi Adsorption On The Fivefold Surface Of I-Al70pd21mn9, J. A. Smerdon, J. K. Parle, L. H. Wearing, Thomas A. Lograsso, A. R. Ross, R. Mcgrath

Ames Laboratory Publications

Scanning tunneling microscopy has been used to study the formation of a Bi monolayer deposited on the fivefold surface of i-Al70Pd21Mn9. Upon deposition of low submonolayer coverages, the nucleation of pentagonal clusters of Bi adatoms of edge length 4.9 Å is observed. The clusters have a common orientation leading to a film with fivefold symmetry. By inspection of images where both the underlying surface and the Bi atoms are resolved, the pentagonal clusters are proposed to nucleate on pseudo-Mackay clusters truncated such that a Mn atom lies centrally in the surface plane. The density ...


Magnetic Phase Transitions And Ferromagnetic Short-Range Correlations In Single-Crystal Tb5si2.2ge1.8, Min Zou, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso Jul 2008

Magnetic Phase Transitions And Ferromagnetic Short-Range Correlations In Single-Crystal Tb5si2.2ge1.8, Min Zou, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso

Ames Laboratory Publications

Magnetic phase transitions in a Tb5Si2.2Ge1.8 single crystal have been studied as a function of temperature and magnetic field. Magnetic-field dependencies of the critical temperatures are highly anisotropic for both the main magnetic ordering process occurring around 120 K and a spin reorientation transition at ∼70 K. Magnetic-field-induced phase transitions occur with the magnetic field applied isothermally along the a and b axes (but not along the c axis) between 1.8 and 70 K in fields below 70 kOe. Strong anisotropic thermal irreversibility is observed in the Griffiths phase regime between 120 ...


Structural Transition And Anisotropic Properties Of Single-Crystalline Srfe2as2, J.-Q. Yan, Andreas Kreyssig, Shibabrata Nandi, N. Ni, Sergey L. Bud'ko, Robert J. Mcqueeney, R. William Mccallum, Thomas A. Lograsso, Alan I. Goldman, Paul C. Canfield Jul 2008

Structural Transition And Anisotropic Properties Of Single-Crystalline Srfe2as2, J.-Q. Yan, Andreas Kreyssig, Shibabrata Nandi, N. Ni, Sergey L. Bud'ko, Robert J. Mcqueeney, R. William Mccallum, Thomas A. Lograsso, Alan I. Goldman, Paul C. Canfield

Ames Laboratory Publications

Platelike single crystals of SrFe2As2 as large as 3×3×0.5 mm3 have been grown out of Sn flux. The SrFe2As2 single crystals show a structural phase transition from a high-temperature tetragonal phase to a low-temperature orthorhombic phase at To=198 K, and do not show any sign of superconductivity down to 1.8 K. The structural transition is accompanied by an anomaly in the electrical resistivity, Hall resistivity, specific heat, and the anisotropic magnetic susceptibility. In an intermediate temperature range from 198 to 160 K, single-crystal x-ray diffraction suggests a coexistence ...


Self-Assembly, Structure, And Electronic Properties Of A Quasiperiodic Lead Monolayer, J. Ledieu, L. Leung, L. H. Wearing, R. Mcgrath, Thomas A. Lograsso, D. Wu, V. Fournée Feb 2008

Self-Assembly, Structure, And Electronic Properties Of A Quasiperiodic Lead Monolayer, J. Ledieu, L. Leung, L. H. Wearing, R. Mcgrath, Thomas A. Lograsso, D. Wu, V. Fournée

Ames Laboratory Publications

A quasiperiodic Pb monolayer has been formed on the fivefold surface of the Al-Pd-Mn quasicrystal. Growth of the monolayer proceeds via self-assembly of an interconnected network of pentagonal Pb stars, which are shown to be τ inflated compared to similar structural elements of the quasiperiodic substrate. Measurements of the electronic structure of the system using scanning tunneling spectroscopy and ultraviolet photoemission spectroscopy reveal that the Pb monolayer displays a pseudogap at the Fermi level which is directly related to its quasiperiodic structure.


Spin-Flop Transition In Gd5ge4 Observed By X-Ray Resonant Magnetic Scattering And First-Principles Calculations Of Magnetic Anisotropy, L. Tan, Andreas Kreyssig, Shibabrata Nandi, S. Jia, Yongbin Lee, J. C. Lang, Z. Islam, Thomas A. Lograsso, Deborah L. Schlagel, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Paul C. Canfield, Bruce N. Harmon, Robert J. Mcqueeney, Alan I. Goldman Feb 2008

Spin-Flop Transition In Gd5ge4 Observed By X-Ray Resonant Magnetic Scattering And First-Principles Calculations Of Magnetic Anisotropy, L. Tan, Andreas Kreyssig, Shibabrata Nandi, S. Jia, Yongbin Lee, J. C. Lang, Z. Islam, Thomas A. Lograsso, Deborah L. Schlagel, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Paul C. Canfield, Bruce N. Harmon, Robert J. Mcqueeney, Alan I. Goldman

Ames Laboratory Publications

X-ray resonant magnetic scattering was employed to study a fully reversible spin-flop transition in orthorhombic Gd5Ge4 and to elucidate details of the magnetic structure in the spin-flop phase. The orientation of the moments at the three Gd sites flop 90° from the c axis to the a axis when a magnetic field, Hsf=9 kOe, is applied along the c axis at T=9 K. The magnetic space group changes from Pnm′a to Pn′m′a′ for all three Gd sublattices. The magnetic anisotropy energy determined from experimental measurements is in good agreement with the ...


Effect Of Interstitial Additions On Magnetostriction In Fe–Ga Alloys, Mianliang Huang, Thomas A. Lograsso, A. E. Clark, J. B. Restorff, M. Wun-Fogle Jan 2008

Effect Of Interstitial Additions On Magnetostriction In Fe–Ga Alloys, Mianliang Huang, Thomas A. Lograsso, A. E. Clark, J. B. Restorff, M. Wun-Fogle

Ames Laboratory Conference Papers, Posters, and Presentations

The additions of trace amounts of small interstitial atoms (carbon, boron, and nitrogen) to Fe–Ga (Galfenol) alloys have a small but beneficial effect on the magnetostriction of Fe–Ga alloys especially at high Ga compositions. The saturated magnetostrictions [(3/2)λ100’s] of both slow cooled and quenched single crystal Fe–Ga–C alloys with Ga contents >18 at. % are about 10%–30% higher than those of the comparable binary Fe–Ga alloys. For boron and nitrogen additions, the magnetostrictions of slow cooled alloys with Ga content >18 at. % were approximately 20% higher than those of the binary ...


Temperature Dependence Of The Magnetostriction And Magnetoelastic Coupling In Fe100−Xalx (X = 14.1,16.6,21.5,26.3) And Fe50co50, A. E. Clark, J. B. Restorff, M. Wun-Fogle, D. Wu, Thomas A. Lograsso Jan 2008

Temperature Dependence Of The Magnetostriction And Magnetoelastic Coupling In Fe100−Xalx (X = 14.1,16.6,21.5,26.3) And Fe50co50, A. E. Clark, J. B. Restorff, M. Wun-Fogle, D. Wu, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

In this paper, we report magnetostriction measurements, (λ100) on Fe-rich Fe–Al alloys and Fe50Co50 as functions of temperature from 77 K to room temperature (RT). From these measurements and elastic constant (c′) measurements, the tetragonal magnetoelastic coupling constants (b1’s) were calculated. Significant differences were found between our RT measurements and earlier magnetostriction measurements for the higher Al concentration alloys (16.6%, 21.5%, 26.3% Al) and the Fe50Co50 alloy. Reminiscent of the temperature dependence of λ100 for pure Fe, magnetostriction changes with temperature are minimal for Fe–Al ...


Magnetostriction Of Iron-Germanium Single Crystals, D. Wu, Qingfeng Xing, R. William Mccallum, Thomas A. Lograsso Jan 2008

Magnetostriction Of Iron-Germanium Single Crystals, D. Wu, Qingfeng Xing, R. William Mccallum, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

The addition of nonmagnetic Ga into body-centered cubic Fe enhances the magnetostriction constant λ100 over tenfold. Literature reports for substitution of Ge at low concentrations suggest that the addition of Ge also enhances the magnetostriction. In this work, the magnetostriction and microstructure of Fe–Ge were investigated to correlate magnetostriction with microstructure. The magnetostriction of Fe100−xGexsingle crystals with x between 0.05 and 0.18 varies with Ge concentration and correlates with phase changes. The value of (3/2)λ100 increases with Ge additions in the A2 single phase region (up to x ...


17o And 51v Nmr For The Zigzag Spin-1 Chain Compound Cav2o4, X. Zong, B. J. Suh, A. Niazi, J.-Q. Yan, Deborah L. Schlagel, Thomas A. Lograsso, David C. Johnston Jan 2008

17o And 51v Nmr For The Zigzag Spin-1 Chain Compound Cav2o4, X. Zong, B. J. Suh, A. Niazi, J.-Q. Yan, Deborah L. Schlagel, Thomas A. Lograsso, David C. Johnston

Ames Laboratory Publications

51V NMR studies on CaV2O4 single crystals and 17O NMR studies on 17O-enriched powder samples are reported. The temperature dependences of the 17O NMR linewidth and nuclear spin-lattice relaxation rate give strong evidence for a long-range antiferromagnetic transition at TN=78 K in the powder. Magnetic susceptibility measurements show that TN=69 K in the crystals. A zero-field 51V NMR signal was observed at low temperatures (f≈237 MHz at 4.2 K) in the crystals. The field-swept spectra with the field in different directions suggest the presence of two antiferromagnetic substructures. Each substructure is ...