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Full-Text Articles in Physics

Exact Island-Size Distributions For Submonolayer Deposition: Influence Of Correlations Between Island Size And Separation, M. C. Bartelt, James W. Evans Dec 1996

Exact Island-Size Distributions For Submonolayer Deposition: Influence Of Correlations Between Island Size And Separation, M. C. Bartelt, James W. Evans

Mathematics Publications

We determine the exact scaling form of the size distribution of islands created via homogeneous nucleation and growth during submonolayer deposition. This scaling form is shown to be controlled by the dependence on size of the propensity for islands to capture diffusing adatoms. This size dependence is determined directly from simulations. It is distinct from mean-field predictions, reflecting strong correlations between island size and separation.


Optical Properties And Electronic Structures Of Equiatomic Xti (X=Fe,Co,Andni) Alloys, Joo Yull Rhee, Bruce N. Harmon, David W. Lynch Dec 1996

Optical Properties And Electronic Structures Of Equiatomic Xti (X=Fe,Co,Andni) Alloys, Joo Yull Rhee, Bruce N. Harmon, David W. Lynch

Physics and Astronomy Publications

The dielectric functions of equiatomic XTi (X=Fe,Co,andNi) alloys in the B2 phase (cubic CsCl structure) were measured by spectroscopic ellipsometry in the energy range of 1.5-5.4 eV. The optical conductivity spectra show close resemblance to each other with a peak at 1.9-2.3 eV and another at 3.1-3.4 eV. Fine structures observed in previously reported measurements were not seen. The band structures and the optical conductivity spectra were calculated in the B2 phase using the linearized-augmented-plane-wave method with the local density approximation. The agreement between the measured and calculated spectra is markedly ...


Photoelectron Spectra Of An Al70pd21mn9 Quasicrystal And The Cubic Alloy Al60pd25mn15, Cynthia J. Jenks, S.-L. Chang, James W. Anderegg, Patricia A. Thiel, David W. Lynch Sep 1996

Photoelectron Spectra Of An Al70pd21mn9 Quasicrystal And The Cubic Alloy Al60pd25mn15, Cynthia J. Jenks, S.-L. Chang, James W. Anderegg, Patricia A. Thiel, David W. Lynch

Physics and Astronomy Publications

Photoelectron spectra of a fivefold quasicrystalline alloy Al70Pd21Mn9 and a related cubic alloy Al60Pd25Mn15 reveal two noteworthy features. The first is that the Pd 3d lines fall at binding energies which are 2.2 eV higher than in pure Pd. A similar shift is observed for Pd in other alloys. The second noteworthy feature is that the Mn 2p32 line is very sharp in the quasicrystal. Fitting the experimental peaks with a Doniach-Sunjic line shpae suggests that the position and density of Mn states near EF is very sensitive to the structural and/or chemical environment of Mn in the ...


Photoelectron Spectra Of An Al70pd21mn9 Quasicrystal And The Cubic Alloy Al60pd25mn15, Cynthia J. Jenks, S.-L. Chang, James W. Anderegg, Patricia A. Thiel, David W. Lynch Sep 1996

Photoelectron Spectra Of An Al70pd21mn9 Quasicrystal And The Cubic Alloy Al60pd25mn15, Cynthia J. Jenks, S.-L. Chang, James W. Anderegg, Patricia A. Thiel, David W. Lynch

Chemistry Publications

Photoelectron spectra of a fivefold quasicrystalline alloy Al70Pd21Mn9 and a related cubic alloy Al60Pd25Mn15 reveal two noteworthy features. The first is that the Pd 3dlines fall at binding energies which are 2.2 eV higher than in pure Pd. A similar shift is observed for Pd in other alloys. The second noteworthy feature is that the Mn 2p3/2 line is very sharp in the quasicrystal. Fitting the experimental peaks with a Doniach-Sunjic line shpae suggests that the position and density of Mn states near EFis very ...


Valence-Band Dispersion In Angle-Resolved Resonant Photoemission From Lasb, C. G. Olson, P. J. Benning, Michael Schmidt, David W. Lynch, Paul C. Canfield, David Michael Wieliczka May 1996

Valence-Band Dispersion In Angle-Resolved Resonant Photoemission From Lasb, C. G. Olson, P. J. Benning, Michael Schmidt, David W. Lynch, Paul C. Canfield, David Michael Wieliczka

Physics and Astronomy Publications

Angle-resolved photoemission spectra taken on single crystals of LaSb at the La 4d→4f resonance show dispersion of resonantly emitted valence-band electrons. This is the first direct demonstration that the Bloch component of valence states participates in resonant photoemission.


Modeling Of Permanent Magnets: Interpretation Of Parameters Obtained From The Jiles–Atherton Hysteresis Model, L. H. Lewis, J. Gao, David C. Jiles, D. O. Welch Apr 1996

Modeling Of Permanent Magnets: Interpretation Of Parameters Obtained From The Jiles–Atherton Hysteresis Model, L. H. Lewis, J. Gao, David C. Jiles, D. O. Welch

Ames Laboratory Publications

The Jiles–Atherton theory is based on considerations of the dependence of energy dissipation within a magnetic material resulting from changes in its magnetization. The algorithm based on the theory yields five computed model parameters, M S , a, α, k, and c, which represent the saturation magnetization, the effective domain density, the mean exchange coupling between the effective domains, the flexibility of domain walls and energy‐dissipative features in the microstructure, respectively. Model parameters were calculated from the algorithm and linked with the physical attributes of a set of three related melt‐quenched permanent magnets based on the Nd2 ...


Dependence Of Energy Dissipation On Annealing Temperature Of Melt–Spun Ndfeb Permanent Magnet Materials, Z. Gao, David C. Jiles, Daniel J. Branagan, R. William Mccallum Apr 1996

Dependence Of Energy Dissipation On Annealing Temperature Of Melt–Spun Ndfeb Permanent Magnet Materials, Z. Gao, David C. Jiles, Daniel J. Branagan, R. William Mccallum

Ames Laboratory Publications

A model of magnetic hysteresis which was developed originally for soft magnetic materials has been applied to melt–spun ribbons of Nd2Fe14B‐based material. The crucial ideas in the model description of hysteresis center on a dissipation of energy due to hysteresis which is proportional to the change in magnetization. The Nd2Fe14B material was melt–spun amorphous and then annealed for a period of 24 h at temperatures ranging from 700 to 950 °C. This resulted in different grain sizes, depending on annealing temperature. Consequently the hysteresis curves represent the properties of ...


Effects Of Surface Condition On Barkhausen Emissions From Steel, Anthony P. Parakka, David C. Jiles, H. Gupta, S. Jalics Apr 1996

Effects Of Surface Condition On Barkhausen Emissions From Steel, Anthony P. Parakka, David C. Jiles, H. Gupta, S. Jalics

Center for Nondestructive Evaluation Publications

Temperature changes during mechanical processing such as grinding of steel parts can cause phase changes in the microstructure. Thermal shock during the process can give rise to localized surface residual stress. The net result can be reduced wear resistance and fatigue life leading to early failure during service. Effective methods for the detection of such damage are necessary. Barkhausen emissions, which arise from discontinuous motion of domain walls, are sensitive to microstructual changes that affect domain dynamics. Detected Barkhausen signals are predominantly from a surface layer about 200 μm thick, those from deeper being attenuated due to eddy currents. An ...


The Magnetomechanical Effect In Electrolytic Iron, Michael K. Devine, David C. Jiles Apr 1996

The Magnetomechanical Effect In Electrolytic Iron, Michael K. Devine, David C. Jiles

Ames Laboratory Publications

The effect of stress on the magnetization of high purity iron has been studied systematically at different locations on the M,H plane corresponding to a variety of magnetic states of the material. The results confirm earlier studies that show the sign of the derivative dM/dσ changes at different locations on the M,H plane, and can even change as a result of a monotonic increase of stress either in compression or tension. The observed behavior can be explained on the basis of a recent theory which predicts that the irreversible changes in magnetization resulting from changes in ...


Enhancement Of Piezomagnetic Response Of Highly Magnetostrictive Rare Earth‐Iron Alloys At Khz Frequencies, Patricia P. Pulvirenti, David C. Jiles, R. D. Greenough, I. M. Reed Apr 1996

Enhancement Of Piezomagnetic Response Of Highly Magnetostrictive Rare Earth‐Iron Alloys At Khz Frequencies, Patricia P. Pulvirenti, David C. Jiles, R. D. Greenough, I. M. Reed

Ames Laboratory Publications

The effects of Al and Si additions on the frequency response of highly magnetostrictive Tb–Dy–Fe alloys have been studied. These elements reduced the electrical conductivity of the material, thereby increasing the depth of penetration of acmagnetic fields and extending the operational frequency range. Complex permeability measurements were made on doped and undoped polycrystalline samples with the objective of studying the improvement in energy conversion efficiency at kilohertz frequencies as a result of the alloying additions. The resulting complex permeability was compared with the values for single crystal specimens of Tb0.3Dy0.7Fe1.92 ...


Hydrogen Charging In Nickel And Iron And Its Effect On Their Magnetic Properties, A. Ramesh, Madhav Rao Govindaraju, David C. Jiles, S. B. Biner, J. M. Roderick Apr 1996

Hydrogen Charging In Nickel And Iron And Its Effect On Their Magnetic Properties, A. Ramesh, Madhav Rao Govindaraju, David C. Jiles, S. B. Biner, J. M. Roderick

Materials Science and Engineering Publications

The current study was undertaken to explore the possibility of detecting hydrogen cavitation in magnetic materials through magnetic propertymeasurements. It is known that dissolved hydrogen in a material causes microvoids. These voids may affect the structure‐sensitive magnetic properties such as coercivity and remanence. In this study, hydrogen was introduced into nickel and iron by two processes, namely thermal charging and cathodic charging. The effect on the magnetic properties was measured. In addition, the variation of the magnetic properties with porosity was studied.


Percolative Diffusion Of Co During Co Oxidation On Pt(100), Michael Joseph Tammaro, James W. Evans Mar 1996

Percolative Diffusion Of Co During Co Oxidation On Pt(100), Michael Joseph Tammaro, James W. Evans

Mathematics Publications

During CO-oxidation on Pt(100), CO diffuses in a "disordered environment" produced by a complex pattern of reconstructed and unreconstructed regions of the substrate. Macroscopic diffusion of CO is effectively only possible on percolating 1X1-regions of the substrate. We treat the spatio-temporal behavior observed in this reaction system accounting in the simple way for the percolative nature of CO-diffusion. This is done via incorporation into the reaction-diffusion equations of a suitable chemical diffusion coefficient, exploiting ideas from the theory of transport in disordered media. We use these equations to analyze the propagation of reactive, O-rich pulses into a CO-covered 1X1-background.