1,345 research outputs found
A composition theorem for the Fourier Entropy-Influence conjecture
The Fourier Entropy-Influence (FEI) conjecture of Friedgut and Kalai [FK96]
seeks to relate two fundamental measures of Boolean function complexity: it
states that holds for every Boolean function , where
denotes the spectral entropy of , is its total influence,
and is a universal constant. Despite significant interest in the
conjecture it has only been shown to hold for a few classes of Boolean
functions.
Our main result is a composition theorem for the FEI conjecture. We show that
if are functions over disjoint sets of variables satisfying the
conjecture, and if the Fourier transform of taken with respect to the
product distribution with biases satisfies the conjecture,
then their composition satisfies the conjecture. As
an application we show that the FEI conjecture holds for read-once formulas
over arbitrary gates of bounded arity, extending a recent result [OWZ11] which
proved it for read-once decision trees. Our techniques also yield an explicit
function with the largest known ratio of between and
, improving on the previous lower bound of 4.615
Antiferromagnetic phase of the gapless semiconductor V3Al
Discovering new antiferromagnetic compounds is at the forefront of developing
future spintronic devices without fringing magnetic fields. The
antiferromagnetic gapless semiconducting D03 phase of V3Al was successfully
synthesized via arc-melting and annealing. The antiferromagnetic properties
were established through synchrotron measurements of the atom-specific magnetic
moments, where the magnetic dichroism reveals large and oppositely-oriented
moments on individual V atoms. Density functional theory calculations confirmed
the stability of a type G antiferromagnetism involving only two-third of the V
atoms, while the remaining V atoms are nonmagnetic. Magnetization, x-ray
diffraction and transport measurements also support the antiferromagnetism.
This archetypal gapless semiconductor may be considered as a cornerstone for
future spintronic devices containing antiferromagnetic elements.Comment: Accepted to Physics Review B on 02/23/1
Magnetic properties of Fe/Dy multilayers: a Monte Carlo investigation
We investigate the magnetic properties of a Heisenberg ferrimagnetic
multilayer by using Monte Carlo simulations. The aim of this work is to study
the local structural anisotropy model which is a possible origin of the
perpendicular magnetic anisotropy in transition metal/rare earth amorphous
multilayers. We have considered a face centered cubic lattice where each site
is occupied by a classical Heisenberg spin. We have introduced in our model of
amorphous multilayers a small fraction of crystallized Fe-Dy nanoclusters with
a mean anisotropy axis along the deposition direction. We show that a
competition in the energy terms takes place between the mean uniaxial
anisotropy of the Dy atoms in the nanoclusters and the random anisotropy of the
Dy atoms in the matrix.Comment: accepte pour publication - Proceeding of the Joint European Magnetic
Symposia (JEMS 06) - Journal of Magnetism and Magnetic Material
Proximity Driven Enhanced Magnetic Order at Ferromagnetic Insulator / Magnetic Topological Insulator Interface
Magnetic exchange driven proximity effect at a magnetic insulator /
topological insulator (MI/TI) interface provides a rich playground for novel
phenomena as well as a way to realize low energy dissipation quantum devices.
Here we report a dramatic enhancement of proximity exchange coupling in the MI
/ magnetic-TI EuS / SbVTe hybrid heterostructure, where V
doping is used to drive the TI (SbTe) magnetic. We observe an
artificial antiferromagnetic-like structure near the MI/TI interface, which may
account for the enhanced proximity coupling. The interplay between the
proximity effect and doping provides insights into controllable engineering of
magnetic order using a hybrid heterostructure.Comment: 5 pages, 4 figure
Monte Carlo investigation of the magnetic anisotropy in Fe/Dy multilayers
By Monte Carlo simulations in the canonical ensemble, we have studied the
magnetic anisotropy in Fe/Dy amorphous multilayers. This work has been
motivated by experimental results which show a clear correlation between the
magnetic perpendicular anisotropy and the substrate temperature during
elaboration of the samples. Our aim is to relate macroscopic magnetic
properties of the multilayers to their structure, more precisely their
concentration profile. Our model is based on concentration dependent exchange
interactions and spin values, on random magnetic anisotropy and on the
existence of locally ordered clusters that leads to a perpendicular
magnetisation. Our results evidence that a compensation point occurs in the
case of an abrupt concentration profile. Moreover, an increase of the
noncollinearity of the atomic moments has been evidenced when the Dy anisotropy
constant value grows. We have also shown the existence of inhomogeneous
magnetisation profiles along the samples which are related to the concentration
profiles
Prediction of Ferromagnetic Ground State of NaCl-type FeN
Ab-initio results for structural and electronic properties of NaCl-type FeN
are presented in a framework of plane-wave and ultrasoft pseudopotentials.
Competition among different magnetic ordering is examined. We find the
ferromagnetic phase stable overall. Stabilization over the unpolarized phase is
obtained by splitting one flat t_2g-type band crossing the Fermi energy. A
comparison with CrN is considered. We find large differences in the properties
of the two systems that can be addressed to the smaller ionicity and
magnetization of FeN.Comment: 5 pages, 4 figures, twocolumn latex style Sentence changed in Section
III line 1
- …