38,783 research outputs found
Anisotropy study of multiferroicity in the pyroxene NaFeGeO
We present a study of the anisotropy of the dielectric, magnetic and
magnetoelastic properties of the multiferroic clinopyroxene NaFeGeO.
Pyroelectric currents, dielectric constants and magnetic susceptibilities as
well as the thermal expansion and the magnetostriction were examined on large
synthetic single crystals of NaFeGeO. The spontaneous electric
polarization detected below K in an
antiferromagnetically ordered state ( K) is mainly lying
within the plane with a small component along , indicating a triclinic
symmetry of the multiferroic phase of NaFeGeO. The electric
polarization can be strongly modified by applying magnetic fields along
different directions. We derive detailed magnetic-field versus temperature
phase diagrams and identify three multiferroic low-temperature phases, which
are separated by a non-ferroelectric, antiferromagnetically ordered state from
the paramagnetic high-temperature phase.Comment: 14 pages, 8 figures. (minor modifications and corrections of the
text
Magnetoelectric properties of [FeCl(HO)] with K, Rb, Cs
The compounds [FeCl(HO)] with K, Rb, Cs are identified as
new linear magnetoelectric materials. We present a detailed investigation of
their linear magnetoelectric properties by measurements of pyroelectric
currents, dielectric constants and magnetization. The anisotropy of the linear
magnetoelectric effect of the K-based and Rb-based compound is consistent with
the magnetic point group , already reported in literature. A symmetry
analysis of the magnetoelectric effect of the Cs-based compound allows to
determine the magnetic point group and to develop a model for its
magnetic structure. In addition, magnetic-field versus temperature phase
diagrams are derived and compared to the closely related multiferroic
(NH)[FeCl(HO)].Comment: 17 pages, 10 figures (updated to the weakly revised version that has
been accepted for publication
Explaining Jupiter's magnetic field and equatorial jet dynamics
Spacecraft data reveal a very Earth-like Jovian magnetic field. This is
surprising since numerical simulations have shown that the vastly different
interiors of terrestrial and gas planets can strongly affect the internal
dynamo process. Here we present the first numerical dynamo that manages to
match the structure and strength of the observed magnetic field by embracing
the newest models for Jupiter's interior. Simulated dynamo action primarily
occurs in the deep high electrical conductivity region while zonal flows are
dynamically constrained to a strong equatorial jet in the outer envelope of low
conductivity. Our model reproduces the structure and strength of the observed
global magnetic field and predicts that secondary dynamo action associated to
the equatorial jet produces banded magnetic features likely observable by the
Juno mission. Secular variation in our model scales to about 2000 nT per year
and should also be observable during the one year nominal mission duration.Comment: 7 pages, 4 figures, accepted for publication in Geophysical Research
Letter
Integral field spectroscopy of QSO host galaxies
We describe a project to study the state of the ISM in ~20 low redshift
(z<0.3) QSO host galaxies observed with the PMAS integral field spectrograph.
We describe method developement to access the stellar and gas component of the
spectrum without the strong nuclear emission to access the host galaxy
properties also in the central region. It shows that integral field
spectroscopy promises to be very efficient to study the gas distribution and
its velocity field, and also spatially resolved stellar population in the host
galaxies also of luminous AGN.Comment: 4 pages, 6 figures, Euro3D Science Workshop, Cambridge, May 2003, AN,
accepte
On the Bekenstein-Hawking Entropy, Non-Commutative Branes and Logarithmic Corrections
We extend earlier work on the origin of the Bekenstein-Hawking entropy to
higher-dimensional spacetimes. The mechanism of counting states is shown to
work for all spacetimes associated with a Euclidean doublet
of electric-magnetic dual brane pairs of type II
string-theory or M-theory wrapping the spacetime's event horizon plus the
complete internal compactification space. Non-Commutativity on the brane
worldvolume enters the derivation of the Bekenstein-Hawking entropy in a
natural way. Moreover, a logarithmic entropy correction with prefactor 1/2 is
derived.Comment: 17 pages, 2 figures; refs. adde
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