1,738 research outputs found
Simple Lattice-Models of Ion Conduction: Counter Ion Model vs. Random Energy Model
The role of Coulomb interaction between the mobile particles in ionic
conductors is still under debate. To clarify this aspect we perform Monte Carlo
simulations on two simple lattice models (Counter Ion Model and Random Energy
Model) which contain Coulomb interaction between the positively charged mobile
particles, moving on a static disordered energy landscape. We find that the
nature of static disorder plays an important role if one wishes to explore the
impact of Coulomb interaction on the microscopic dynamics. This Coulomb type
interaction impedes the dynamics in the Random Energy Model, but enhances
dynamics in the Counter Ion Model in the relevant parameter range.Comment: To be published in Phys. Rev.
Influence of external magnetic fields on growth of alloy nanoclusters
Kinetic Monte Carlo simulations are performed to study the influence of
external magnetic fields on the growth of magnetic fcc binary alloy
nanoclusters with perpendicular magnetic anisotropy. The underlying kinetic
model is designed to describe essential structural and magnetic properties of
CoPt_3-type clusters grown on a weakly interacting substrate through molecular
beam epitaxy. The results suggest that perpendicular magnetic anisotropy can be
enhanced when the field is applied during growth. For equilibrium bulk systems
a significant shift of the onset temperature for L1_2 ordering is found, in
agreement with predictions from Landau theory. Stronger field induced effects
can be expected for magnetic fcc-alloys undergoing L1_0 ordering.Comment: 10 pages, 3 figure
Hopping Transport in the Presence of Site Energy Disorder: Temperature and Concentration Scaling of Conductivity Spectra
Recent measurements on ion conducting glasses have revealed that conductivity
spectra for various temperatures and ionic concentrations can be superimposed
onto a common master curve by an appropriate rescaling of the conductivity and
frequency. In order to understand the origin of the observed scaling behavior,
we investigate by Monte Carlo simulations the diffusion of particles in a
lattice with site energy disorder for a wide range of both temperatures and
concentrations. While the model can account for the changes in ionic activation
energies upon changing the concentration, it in general yields conductivity
spectra that exhibit no scaling behavior. However, for typical concentrations
and sufficiently low temperatures, a fairly good data collapse is obtained
analogous to that found in experiment.Comment: 6 pages, 4 figure
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