5,277 research outputs found
Roughening and preroughening in the six vertex model with an extended range of interaction
We study the phase diagram of the BCSOS model with an extended interaction
range using transfer matrix techniques, pertaining to the (100) surface of
single component fcc and bcc crystals. The model shows a 2x2 reconstructed
phase and a disordered flat phase. The deconstruction transition between these
phases merges with a Kosterlitz-Thouless line, showing an interplay of Ising
and Gaussian degrees of freedom. As in studies of the fully frustrated XY
model, exponents deviating from Ising are found. We conjecture that
tri-critical Ising behavior may be a possible explanation for the non-Ising
exponents found in those models.Comment: 25 pages in RevTeX 3.0, seven uuencoded postscript figures, REPLACED
because of submission error (figures were not included
Is surface melting a surface phase transition?
Monte Carlo or Molecular Dynamics calculations of surfaces of Lennard-Jones
systems often indicate, apart from a gradual disordering of the surface called
surface melting, the presence of a phase transition at the surface, but cannot
determine the nature of the transition. In the present paper, we provide for a
link between the continuous Lennard-Jones system and a lattice model. We apply
the method for the (001) surface of a Lennard-Jones fcc structure pertaining to
Argon. The corresponding lattice model is a Body Centered Solid on Solid model
with an extended range of interaction, showing in principle rough, flat and
disordered flat phases. We observe that entropy effects considerably lower the
strength of the effective couplings between the atoms. The Argon (001) face is
shown to exhibit a phase transition at T=70.5 +- 0.5 K, and we identify this
transition as roughening. The roughening temperature is in good correspondence
with experimental results for Argon.Comment: 17 pages REVTeX, 14 uuencoded postscript figures appende
X-ray photoelectron emission microscopy in combination with x-ray magnetic circular dichroism investigation of size effects on field-induced N\'eel-cap reversal
X-ray photoelectron emission microscopy in combination with x-ray magnetic
circular dichroism is used to investigate the influence of an applied magnetic
field on N\'eel caps (i.e., surface terminations of asymmetric Bloch walls).
Self-assembled micron-sized Fe(110) dots displaying a moderate distribution of
size and aspect ratios serve as model objects. Investigations of remanent
states after application of an applied field along the direction of N\'eel-cap
magnetization give clear evidence for the magnetization reversal of the N\'eel
caps around 120 mT, with a 20 mT dispersion. No clear correlation could be
found between the value of the reversal field and geometrical features of the
dots
Influence of topography and Co domain walls on the magnetization reversal of the FeNi layer in FeNi/AlO/Co magnetic tunnel junctions
We have studied the magnetization reversal dynamics of FeNi/AlO/Co
magnetic tunnel junctions deposited on step-bunched Si substrates using
magneto-optical Kerr effect and time-resolved x-ray photoelectron emission
microscopy combined with x-ray magnetic circular dichroism (XMCD-PEEM).
Different reversal mechanisms have been found depending on the substrate miscut
angle. Larger terraces (smaller miscut angles) lead to a higher nucleation
density and stronger domain wall pinning. The width of domain walls with
respect to the size of the terraces seems to play an important role in the
reversal. We used the element selectivity of XMCD-PEEM to reveal the strong
influence of the stray field of domain walls in the hard magnetic layer on the
magnetic switching of the soft magnetic layer.Comment: 8 Pages, 7 Figure
Dynamics of magnetic domain wall motion after nucleation: Dependence on the wall energy
The dynamics of magnetic domain wall motion in the FeNi layer of a
FeNi/Al2O3/Co trilayer has been investigated by a combination of x-ray magnetic
circular dichroism, photoelectron emission microscopy, and a stroboscopic
pump-probe technique. The nucleation of domains and subsequent expansion by
domain wall motion in the FeNi layer during nanosecond-long magnetic field
pulses was observed in the viscous regime up to the Walker limit field. We
attribute an observed delay of domain expansion to the influence of the domain
wall energy that acts against the domain expansion and that plays an important
role when domains are small.Comment: Accepted for publication in Physical Review Letter
On the scaling behaviour of cross-tie domain wall structures in patterned NiFe elements
The cross-tie domain wall structure in micrometre and sub-micrometre wide
patterned elements of NiFe, and a thickness range of 30 to 70nm, has been
studied by Lorentz microscopy. Whilst the basic geometry of the cross-tie
repeat units remains unchanged, their density increases when the cross-tie
length is constrained to be smaller than the value associated with a continuous
film. This occurs when element widths are sufficiently narrow or when the wall
is forced to move close to an edge under the action of an applied field. To a
very good approximation the cross-tie density scales with the inverse of the
distance between the main wall and the element edge. The experiments show that
in confined structures, the wall constantly modifies its form and that the need
to generate, and subsequently annihilate, extra vortex/anti-vortex pairs
constitutes an additional source of hysteresis.Comment: 4 pages, 5 figures, accepted for publication in Europhysics Letters
(EPL
Sawja: Static Analysis Workshop for Java
Static analysis is a powerful technique for automatic verification of
programs but raises major engineering challenges when developing a full-fledged
analyzer for a realistic language such as Java. This paper describes the Sawja
library: a static analysis framework fully compliant with Java 6 which provides
OCaml modules for efficiently manipulating Java bytecode programs. We present
the main features of the library, including (i) efficient functional
data-structures for representing program with implicit sharing and lazy
parsing, (ii) an intermediate stack-less representation, and (iii) fast
computation and manipulation of complete programs
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