504 research outputs found
Radiation kinetics in electronic materials Semiannual report
Degradation and recovery of minority carriers in solar cells including lithiu
DEFECT MOBILITY AND REACTION: DIFFUSIONAL AND RATE THEORY FORMULATIONS IN ONE AND THREE DIMENSIONS.
The migration of defects, leading to eventual reaction, is analyzed on the basis of diffusion theory and compared with chemical rate theory. A diffusional treatment is carried out in detail and in special cases of particular interest. Correlations between interstitials and vacancies, typical of metals following electron irradiation, are examined. Trapping by impurities and dislocations, thermal conversion, and high temperature bombardment are also treated. In each case, formulations are developed along both one- and three-dimensional diffusion models. These alternative results are compared with experiments, particularly annealing in copper irradiated by electrons at low temperature. The results support the conclusion that the defect which migrates in Stage I diffuses in three dimensions
Magnetocaloric effect in two-dimensional spin-1/2 antiferromagnets
The magnetocaloric effect is studied at the transition to saturation in the
antiferromagnetic spin-1/2 Heisenberg model on the simplest two-dimensional
lattices, namely the square and the triangular lattice. Numerical results are
presented for the entropy which are consistent with identical universal
properties. However, the absolute values of the entropy are bigger on the
geometrically frustrated triangular lattice than on the non-frustrated square
lattice, indicating that frustration improves the magnetocaloric properties.Comment: 2 pages, 2 figures included, to appear in Physica B (proceedings of
SCES'05
Novel magnetic phases in a Gd2Ti2O7 pyrochlore for a field applied along the [100] axis
We report on longitudinal and transverse magnetisation measurements performed
on single crystal samples of Gd2Ti2O7 for a magnetic field applied along the
[100] direction. The measurements reveal the presence of previously unreported
phases in fields below 10 kOe in an addition to the higher-field-induced phases
that are also seen for H//[111], [110], and [112]. The proposed H-T phase
diagram for the [100] direction looks distinctly different from all the other
directions studied previously.Comment: 4 pages, 5 figure
Bridging the Information Literacy Gap with Clickers
A Class Performance System (CPS) is applied as an assessment tool to assist in determining the level of information literacy knowledge already possessed by adult students enrolled in a graduate Educational Leadership and Technology program. The CPS data collected reveals that students possess varying degrees of technology expertise and information literacy skills. Study results suggest that clickers facilitate differentiated information literacy pedagogy and increase engagement for graduate students. © 2009 Elsevier Inc. All rights reserved
Spin Dynamics of in the Field-Induced Ordered Phase
- (known as DTN) is a spin-1 material with a strong
single-ion anisotropy that is regarded as a new candidate for Bose-Einstein
condensation (BEC) of spin degrees of freedom. We present a systematic study of
the low-energy excitation spectrum of DTN in the field-induced magnetically
ordered phase by means of high-field electron spin resonance measurements at
temperatures down to 0.45 K. We argue that two gapped modes observed in the
experiment can be consistently interpreted within a four-sublattice
antiferromagnet model with a finite interaction between two tetragonal
subsystems and unbroken axial symmetry. The latter is crucial for the
interpretation of the field-induced ordering in DTN in terms of BEC.Comment: 4 pages, 3 figure
Magnetocaloric effect in pyrochlore antiferromagnet Gd2Ti2O7
An adiabatic demagnetization process is studied in Gd2Ti2O7, a geometrically
frustrated antiferromagnet on a pyrochlore lattice. In contrast to conventional
paramagnetic salts, this compound can exhibit a temperature decrease by a
factor of ten in the temperature range below the Curie-Weiss constant. The most
efficient cooling is observed in the field interval between 120 and 60 kOe
corresponding to a crossover between saturated and spin-liquid phases. This
phenomenon indicates that a considerable part of the magnetic entropy survives
in the strongly correlated state. According to the theoretical model, this
entropy is associated with a macroscopic number of local modes remaining
gapless till the saturation field. Monte Carlo simulations on a classical spin
model demonstrate good agreement with the experiment. The cooling power of the
process is experimentally estimated with a view to possible technical
applications. The results for Gd2Ti2O7 are compared to those for Gd3Ga5O12, a
well-known material for low temperature magnetic refrigeration.Comment: 6 pages, 4 figures, accepted versio
Magnetic excitations in dipolar pyrochlore antiferromagnet GdSnO
The spin dynamics in the geometrically frustrated pyrochlore antiferromagnet
is studied by means of the electron spin resonance. In the
ordered phase ( K), we have detected three gapped resonance modes.
Their values agree well with the developed spin-wave theory which takes into
account the Heisenberg nearest-neighbor exchange, the single-ion anisotropy and
the long-range dipolar interactions. The theory also predicts a fourth
lowest-frequency gap, which lies beyond the experimental range of frequencies,
but determines the exponential decrease of the specific heat at low
temperature.Comment: 8 pages, 5 figure
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