Search Results - (Author, Cooperation:J. Snyder)

2018-01-03

The Society of Nuclear Medicine (SNM)

0022-3123

Medicine

2013-05-11

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2011-05-06

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

2015-04-04

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2015-11-28

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2018-09-04

Rockefeller University Press

0022-1007

1540-9538

Medicine

Cardiovascular Biology, Human Disease Genetics

1089-7550

AIP Digital Archive

Physics

The magnetostatic contribution to perpendicular magnetic anisotropy caused by nonmagnetic grain-boundary layers around the crystals in a hexagonal array of hexagonal columnar crystals has been calculated. Using film thickness and crystal diameter data, and the results of grain-boundary segregation calculations, values of normalized magnetostatic anisotropy constant were calculated, and compared to experimental data on the variation of normalized net anisotropy Knet/2πM2s. It is concluded that the contribution of magnetostatic effects to the variation of normalized anisotropy is negligible. Indeed, for all the films of this study, one can use the continuous thin-film value ( − 2πM2s) for magnetostatic contribution to anisotropy, with at most a 2% error. It is predicted that magnetostatic effects only become appreciable when the nonmagnetic and magnetic dimensions become comparable in size. It is concluded that mechanisms other than magnetostatic effects must be found in order to explain the perpendicular anisotropy in CoCr sputtered films.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We have experimentally determined the CoCr phase diagram in a region of great interest for magnetic recording media, by quantitative thermomagnetic analyses (TMA) of CoCr films. We used TMA results, together with CoCr bulk data, film-average measurements of composition and room temperature Ms, and a novel curve-fitting and analysis technique. Our TMA experiments suggested a model in which magnetic (exchange) energy causes the phase separation. There are four different phase diagrams for CoCr in the literature. Our experimentally determined phase diagram shows good qualitative agreement with the theoretical Hasebe phase diagram [J. Jpn. Inst. Met. 46, 577 (1982) (in Japanese)], the only one whose calculation included magnetic (exchange) energy terms. We have also estimated the relative amounts of the different phases present in the films, and found about 40 to 55 vol % to be nonmagnetic at room temperature. For such material, the magnetostatic contributions to magnetic anisotropy could be substantial.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We have investigated saturation magnetization (Ms) variation and Cr segregation in CoCr rf-sputtered films. Using a special substrate-temperature monitoring system, which provides in situ measurements, the relationships of Ms to substrate temperature (Tsub) and Tsub to sputtering parameters have been investigated for films sputtered from both alloy and mosaic targets. Ms was found to increase as Tsub decreased. Little difference was found between films sputtered from the two different types of targets. A theoretical model has been developed for calculation of equilibrium Cr segregation on grain boundaries. The composition of atomic planes near a grain boundary, depletion of the crystal core, and Ms of the crystals can be calculated as a function of temperature. Although the predicted amount of Cr segregation is in agreement with experimental measurements in the literature, the predicted variation of Ms with temperature is only a small fraction of what is seen experimentally. It is concluded that mechanisms other than Cr segregation must be found to provide the explanation for the variation of Ms in CoCr films.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The magnetic properties and microstructures of a series of as-quenched and heat-treated inert gas atomized (IGA) rare-earth rich (Nd,Dy)–Fe–B particles have been investigated. Heat treatment was found to substantially improve magnetic properties, with effects most pronounced in samples with higher Dy content and higher total rare earth (RE) content. The as-quenched particles consisted of an underquenched dendritic-like structure with the majority phase RE2Fe14B, and a fine network of RE-rich material between the grains. The heat-treated particles showed a change in microstructure which correlated with magnetic property changes. Particles which showed little change in magnetic properties showed no obvious change in microstructure. Particles which showed large changes in magnetic properties showed a large change in microstructure: most of the fine network of RE-rich interdendritic material disappeared, leaving behind only a few small isolated regions. This would seem to indicate that the predominant mechanism determining coercivity in these IGA RE-rich (Nd,Dy)–Fe–B powers is nucleation of reverse domains, rather than domain wall pinning at nonmagnetic intergranular material. © 1999 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Metal-bonded cobalt ferrite composites are promising candidates for torque sensors and other magnetostrictive sensing and actuating applications. In the present study, the temperature dependence of the magnetomechanical effect in a ring-shape cobalt ferrite composite under torsional strain has been investigated in the temperature range of −37 to 90 °C. The changes of external axial magnetic field were measured as a function of applied torque. Magnetomechanical sensitivity of ΔHext/Δτ=65 A N−1 m−2 was observed with a magnetomechanical hysteresis of Δτ=±0.62 N m at room temperature (22 °C). These were then measured as a function of temperature. Both decreased as the temperature increased throughout the entire range. The magnetomechanical hysteresis became negligible at temperatures higher than 60 °C, above which there was a linear change in external magnetic field with applied torque. These temperature dependences are explained by the changes of magnetostriction, anisotropy, spontaneous magnetization, and pinning of domain walls caused by the availability of increased thermal energy. © 2000 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

An ultrahigh vacuum (UHV) surface analysis chamber coupled with a visible light-scattering apparatus is described. This combination of UHV surface analysis capabilities and bidirectional reflectance distribution function measurements permits investigation of effects of various surface treatments such as gas adsorption and ion bombardment on optical scatter. Stray light reflections from the UHV windows and components are temporally rejected by use of a picosecond pulsed laser source and synchronized, time-gated detector. This system allows measurement of optical scatter levels in the range of 10−7 sr−1.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A Sm-poor mixture of Fe-substituted Sm2Co17, having the nominal stoichiometry of Sm0.080Co0.645Fe0.276, was ball-milled to explore the possibility of enhancing its remanence through direct microstructural refinement. With milling, the Sm2(Co0.7Fe0.3)17 compound disassociates to a body-centered-cubic supersaturated SmCoFe solid solution and a residual SmCoFe amorphous phase. Correspondingly, the coercive field values first increase, peaking at 0.83 kOe after 180 min of milling, then decrease with continued milling to 〈0.1 kOe after 1200 min. The remanence, as Mr/Ms, is measured to track closely the coercive field behavior, experiencing modest increases to 0.26 after just 120 min of milling. Magnetization values are found to increase first with the dissociation of the 2:17 phase, and again with the ejection of Sm from the bcc component. © 1997 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Ba-hexaferrite thin films for recording media applications are often fabricated by a two-step process: sputter deposition of an amorphous precursor, followed by annealing to crystallize the BaFe12O19 phase. The magnetic anisotropy of the crystalline films can be either in-plane or perpendicular, depending on the sputtering process used in the first step. However, conventional structural characterization techniques have not been able to distinguish between different as-sputtered films. Using polarization-dependent extended x-ray absorption fine structure (PD-EXAFS), we have observed anisotropic local structure around both Ba and Fe atoms in the amorphous precursor films. Comparison of the results suggests that the amorphous films consist of networks of Fe atoms surrounded by their O nearest neighbors, with Ba atoms fitting into in-between spaces as network modifiers (there might also be some minor Fe network modifying contribution). The local structural anisotropy of the amorphous films appears to determine the orientation of the fast-growing basal plane directions during annealing, and thus the directions of the c axes and the magnetic anisotropy. © 1996 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Thermomagnetic analyses (TMA) of rf-sputtered CoCr films have shown unusual magnetization versus temperature behavior. On heating, magnetization persists to around 700 °C. After cooling from 800 °C, however, magnetization does not appear again until around 300 °C. On all subsequent heatings and coolings, such films retain a Curie temperature of around 300 °C. At the same time, room-temperature Ms values decrease considerably. TMA of bulk samples of the same composition show a Curie temperature around 300 °C and no subsequent change of Curie temperature upon heating and cooling. These data cannot be explained on the basis of Cr-rich oxide formation. Additional experiments have ruled out Cr segregation in a planar transition layer. X-ray and electron diffraction measurements have shown no evidence of long-range order-disorder phenomenon. However, the data are consistent with explanations involving either Cr grain-boundary segregation or atomic-scale redistribution of the Cr. A simple model of grain-boundary segregation has been developed which predicts the expected relationship of average composition and Cr-rich grain boundary width. Minimum widths and minimum composition differences can be calculated.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

The development of diagnostic software for the tokamak fusion test reactor (TFTR) machine is discussed. Key problems in the development process are the control of a large body of applications code and the provision of an environment that maximizes the productivity of the applications programmers. Control of the large body of code is accomplished through the use of a common method of software module specification, standard naming conventions, standard documentation, and automated utility programs to check the consistency of source code. The productivity of the applications programmers is enchanced by the presence of services providing graphics capabilities, terminal and user dialog management, data access, smoothing and compression, hardware device access and testing, and program execution tracing.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

A substrate temperature measurement system is described, which has proved useful for measuring substrate temperature in situ in an rf diode sputtering system. This temperature measurement system mimics the true deposition materials, geometry, and thermal contact as much as possible. The measurement electronics are quite insensitive to rf interference and allow for cancellation of lead resistance and thermoelectric voltages.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The effect of the matrix material on the magnetostriction of composites containing highly magnetostrictive particles has been studied. Experimental results showed that the elastic modulus of the matrix is an important factor determining the bulk magnetostriction of the composite. For a series of composites with the same volume fraction of magnetostrictive particles but different matrix materials, the bulk magnetostriction was found to increase systematically with decreasing elastic modulus of the matrix. A model theory for the magnetostriction of such composites has been developed, based on two limiting assumptions: uniform strain or uniform stress inside the composite. The theory was then used to predict the magnetostriction of the entire material from the volume fractions of the components, their elastic moduli and magnetostrictions. These predictions were in agreement with the experimental results. It is concluded that to obtain a high magnetostriction and adequate mechanical properties of a composite, the elastic moduli of the magnetostrictive phase and the matrix should be as close as possible in value. © 1999 American Institute of Physics.

Electronic Resource

1749-6632

Blackwell Publishing Journal Backfiles 1879-2005

Natural Sciences in General

Electronic Resource

1089-7550

AIP Digital Archive

Physics

CoCr thin films were sputtered with varying values of target bias, forward power, sputtering rate and argon pressure. Cr content, saturation moment, coercivity, squareness, perpendicular anisotropy Ku, and net anisotropy (Ku−2πM2s) were measured. It was found that perpendicular or in-plane squareness measurements with a VSM were not a useful indicator of perpendicular anisotropy (as determined by torque magnetometry). Net perpendicular anisotropy (Ku−2πM2s) was found to increase with deposition rate. Most films showed positive net perpendicular anisotropy, with no substrate heating necessary other than that provided by the sputtering process. Saturation moment was found to decrease with increasing target bias, a variation not explainable by differences in average Cr content. Perpendicular anisotropy and perpendicular coercivity decreased with increasing target bias also. These results suggest a common microstructural mechanism affecting all three properties. Alternate explanations involving oxidation, Cr distribution (short-range order, or segregation of Cr-rich phases), and argon incorporation could explain these results, but will require further experiments to establish.

Electronic Resource