1,605 research outputs found
Symmetry analysis of magneto-optical effects: The case of x-ray diffraction and x-ray absorption at the transition metal L23 edge
A general symmetry analysis of the optical conductivity or scattering tensor
is used to rewrite the conductivity tensor as a sum of fundamental spectra
multiplied by simple functions depending on the local magnetization direction.
Using this formalism, we present several numerical examples at the transition
metal L23 edge. From these numerical calculations we can conclude that large
deviations from the magneto-optical effects in spherical symmetry are found.
These findings are in particular important for resonant x-ray diffraction
experiments where the polarization dependence and azimuthal dependence of the
scattered Bragg intensity is used to determine the local ordered magnetization
direction
Magnetic coupling in highly-ordered NiO/Fe3O4(110): Ultrasharp magnetic interfaces vs. long-range magnetoelastic interactions
We present a laterally resolved X-ray magnetic dichroism study of the
magnetic proximity effect in a highly ordered oxide system, i.e. NiO films on
Fe3O4(110). We found that the magnetic interface shows an ultrasharp
electronic, magnetic and structural transition from the ferrimagnet to the
antiferromagnet. The monolayer which forms the interface reconstructs to
NiFe2O4 and exhibits an enhanced Fe and Ni orbital moment, possibly caused by
bonding anisotropy or electronic interaction between Fe and Ni cations. The
absence of spin-flop coupling for this crystallographic orientation can be
explained by a structurally uncompensated interface and additional
magnetoelastic effects
Morphological stability of electromigration-driven vacancy islands
The electromigration-induced shape evolution of two-dimensional vacancy
islands on a crystal surface is studied using a continuum approach. We consider
the regime where mass transport is restricted to terrace diffusion in the
interior of the island. In the limit of fast attachment/detachment kinetics a
circle translating at constant velocity is a stationary solution of the
problem. In contrast to earlier work [O. Pierre-Louis and T.L. Einstein, Phys.
Rev. B 62, 13697 (2000)] we show that the circular solution remains linearly
stable for arbitrarily large driving forces. The numerical solution of the full
nonlinear problem nevertheless reveals a fingering instability at the trailing
end of the island, which develops from finite amplitude perturbations and
eventually leads to pinch-off. Relaxing the condition of instantaneous
attachment/detachment kinetics, we obtain non-circular elongated stationary
shapes in an analytic approximation which compares favorably to the full
numerical solution.Comment: 12 page
Dynamic Scaling in a 2+1 Dimensional Limited Mobility Model of Epitaxial Growth
We study statistical scale invariance and dynamic scaling in a simple
solid-on-solid 2+1 - dimensional limited mobility discrete model of
nonequilibrium surface growth, which we believe should describe the low
temperature kinetic roughening properties of molecular beam epitaxy. The model
exhibits long-lived ``transient'' anomalous and multiaffine dynamic scaling
properties similar to that found in the corresponding 1+1 - dimensional
problem. Using large-scale simulations we obtain the relevant scaling
exponents, and compare with continuum theories.Comment: 5 pages, 4 ps figures included, RevTe
The process of irreversible nucleation in multilayer growth. II. Exact results in one and two dimensions
We study irreversible dimer nucleation on top of terraces during epitaxial
growth in one and two dimensions, for all values of the step-edge barrier. The
problem is solved exactly by transforming it into a first passage problem for a
random walker in a higher-dimensional space. The spatial distribution of
nucleation events is shown to differ markedly from the mean-field estimate
except in the limit of very weak step-edge barriers. The nucleation rate is
computed exactly, including numerical prefactors.Comment: 22 pages, 10 figures. To appear in Phys. Rev.
Sign-time distributions for interface growth
We apply the recently introduced distribution of sign-times (DST) to
non-equilibrium interface growth dynamics. We are able to treat within a
unified picture the persistence properties of a large class of relaxational and
noisy linear growth processes, and prove the existence of a non-trivial scaling
relation. A new critical dimension is found, relating to the persistence
properties of these systems. We also illustrate, by means of numerical
simulations, the different types of DST to be expected in both linear and
non-linear growth mechanisms.Comment: 4 pages, 5 ps figs, replaced misprint in authors nam
Extremal statistics of curved growing interfaces in 1+1 dimensions
We study the joint probability distribution function (pdf) of the maximum M
of the height and its position X_M of a curved growing interface belonging to
the universality class described by the Kardar-Parisi-Zhang equation in 1+1
dimensions. We obtain exact results for the closely related problem of p
non-intersecting Brownian bridges where we compute the joint pdf P_p(M,\tau_M)
where \tau_M is there the time at which the maximal height M is reached. Our
analytical results, in the limit p \to \infty, become exact for the interface
problem in the growth regime. We show that our results, for moderate values of
p \sim 10 describe accurately our numerical data of a prototype of these
systems, the polynuclear growth model in droplet geometry. We also discuss
applications of our results to the ground state configuration of the directed
polymer in a random potential with one fixed endpoint.Comment: 6 pages, 4 figures. Published version, to appear in Europhysics
Letters. New results added for non-intersecting excursion
Spin dynamics of observed by Electron Spin Resonance
Below the Kondo temperature electron spin resonance (ESR) usually
is not observable from the Kondo-ion itself because the characteristic spin
fluctuation energy results in a huge width of the ESR line. The heavy fermion
metal YbRhSi seems to be an exceptional case where definite ESR
spectra show characteristic properties of the Kondo-ion Yb well
\textit{below} . We found that the spin dynamics of
YbRhSi, as determined by its ESR relaxation, is spatially
characterized by an anisotropy of the zero temperature residual relaxation
only.Comment: Presented at NanoRes 2004, Kazan; 4 pages, 3 Figure
Impurity-induced diffusion bias in epitaxial growth
We introduce two models for the action of impurities in epitaxial growth. In
the first, the interaction between the diffusing adatoms and the impurities is
``barrier''-like and, in the second, it is ``trap''-like. For the barrier
model, we find a symmetry breaking effect that leads to an overall down-hill
current. As expected, such a current produces Edwards-Wilkinson scaling. For
the trap model, no symmetry breaking occurs and the scaling behavior appears to
be of the conserved-KPZ type.Comment: 5 pages(with the 5 figures), latex, revtex3.0, epsf, rotate, multico
Driven Diffusive Systems: How Steady States Depend on Dynamics
In contrast to equilibrium systems, non-equilibrium steady states depend
explicitly on the underlying dynamics. Using Monte Carlo simulations with
Metropolis, Glauber and heat bath rates, we illustrate this expectation for an
Ising lattice gas, driven far from equilibrium by an `electric' field. While
heat bath and Glauber rates generate essentially identical data for structure
factors and two-point correlations, Metropolis rates give noticeably weaker
correlations, as if the `effective' temperature were higher in the latter case.
We also measure energy histograms and define a simple ratio which is exactly
known and closely related to the Boltzmann factor for the equilibrium case. For
the driven system, the ratio probes a thermodynamic derivative which is found
to be dependent on dynamics
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