337 research outputs found
Boundary Energies and the Geometry of Phase Separation in Double--Exchange Magnets
We calculate the energy of a boundary between ferro- and antiferromagnetic
regions in a phase separated double-exchange magnet in two and three
dimensions. The orientation dependence of this energy can significantly affect
the geometry of the phase-separated state in two dimensions, changing the
droplet shape and possibly stabilizing a striped arrangement within a certain
range of the model parameters. A similar effect, albeit weaker, is also present
in three dimensions. As a result, a phase-separated system near the percolation
threshold is expected to possess intrinsic hysteretic transport properties,
relevant in the context of recent experimental findings.Comment: 6 pages, including 4 figures; expanded versio
Reciprocal space study of Heisenberg exchange interactions in ferromagnetic metals
The modern quantum theory of magnetism in solids is getting commonly derived
using Green's functions formalism. The popularity draws itself from remarkable
opportunities to capture the microscopic landscape of exchange interactions,
starting from a tight-binding representation of the electronic structure.
Indeed, the conventional method of infinitesimal spin rotations, considered in
terms of local force theorem, opens vast prospects of investigations regarding
the magnetic environment, as well as pairwise atomic couplings. However, this
theoretical concept practically does not devoid of intrinsic inconsistencies.
In particular, naturally expected correspondence between single and pairwise
infinitesimal spin rotations is being numerically revealed to diverge. In this
work, we elaborate this question on the model example and canonical case of bcc
iron. Our analytical derivations discovered the principal preference of on-site
magnetic precursors if the compositions of individual atomic interactions are
in focus. The problem of extremely slow or even absent spatial convergence
while considering metallic compounds was solved by suggesting the original
technique, based on reciprocal space framework. Using fundamental Fourier
transform-inspired interconnection between suggested technique and traditional
spatial representation, we shed light on symmetry breaking in bcc Fe on the
level of orbitally decomposed total exchange surrounding
To the center of cold spot with Planck
The structure of the cold spot, of a non-Gaussian anomaly in the cosmic
microwave background (CMB) sky first detected by Vielva et al. is studied using
the data by Planck satellite. The obtained map of the degree of stochasticity
(K-map) of CMB for the cold spot, reveals, most clearly in 100 GHz band, a
shell-type structure with a center coinciding with the minima of the
temperature distribution. The shell structure is non-Gaussian at a 4\sigma
confidence level. Such behavior of the K-map supports the void nature of the
cold spot. The applied method can be used for tracing voids that have no
signatures in redshift surveys.Comment: A & A (in press), 4 pages, 5 figures; to match the published versio
FAST PREDETERMINED EQUILIBRIUM DYNAMICS APPLIED TO MAGNETIC SYSTEMS
In this paper, a fast algorithm for implementing the method [1] is proposed for consider-ation. Its application to the problem of modeling microscopic magnetic dynamics is also shown
Messier 81's Planck view vs its halo mapping
This paper is a follow-up of a previous paper about the M82 galaxy and its
halo based on Planck observations. As in the case of M82, so also for the M81
galaxy a substantial North-South and East-West temperature asymmetry is found,
extending up to galactocentric distances of about . The temperature
asymmetry is almost frequency independent and can be interpreted as a
Doppler-induced effect related to the M81 halo rotation and/or triggered by the
gravitational interaction of the galaxies within the M81 Group. Along with the
analogous study of several nearby edge-on spiral galaxies, the CMB temperature
asymmetry method thus is shown to act as a direct tool to map the galactic
haloes and/or the intergalactic bridges, invisible in other bands or by other
methods.Comment: 5 pages, 3 figures, in press in Astronomy and Astrophysics, Main
Journa
Influence of surface modification of nitinol with silicon using plasma-immersion ion implantation on the alloy corrosion resistance in artificial physiological solutions
Cyclic voltammetry and potentiostatic polarization have been applied to study electrochemical behavior and to determine corrosion resistance of nitinol, which surface was modified with silicon using plasma-immersion ion implantation, in 0.9% NaCl solution and in artificial blood plasma. It was found out that continuous, and also homogeneous in composition, thin Si-containing layers are resistant to corrosion damage at high positive potentials in artificial physiological solutions due to formation of stable passive films. Breakdown potential Eb of Si-modified NiTi depends on the character of silicon and Ni distribution at the alloy surface, Eb values amounted to 0.9–1.5 V (Ag/AgCl/KCl sat.) for the alloy samples with continuous Si-containing surface layers and with decreased Ni surface concentration
Planck's confirmation of the M31 disk and halo rotation
Planck's data acquired during the first 15.4 months of observations towards
both the disk and halo of the M31 galaxy are analyzed. We confirm the existence
of a temperature asymmetry, previously detected by using the 7-year WMAP data,
along the direction of the M31 rotation, therefore indicative of a
Doppler-induced effect. The asymmetry extends up to about 10 degrees (about 130
kpc) from the M31 center. We also investigate the recent issue raised in Rubin
and Loeb (2014) about the kinetic Sunyaev-Zeldovich effect from the diffuse hot
gas in the Local Group, predicted to generate a hot spot of a few degrees size
in the CMB maps in the direction of M31, where the free electron optical depth
gets the maximum value. We also consider the issue whether in the opposite
direction with respect to the M31 galaxy the same effect induces a minimum in
temperature in the Planck's maps of the sky. We find that the Planck's data at
100 GHz show an effect even larger than that expected.Comment: 4 pages, 1 table, 2 figures, in press as a Letter in A&
Planck view of the M82 galaxy
Planck data towards the galaxy M82 are analyzed in the 70, 100 and 143 GHz
bands. A substantial north-south and East-West temperature asymmetry is found,
extending up to 1 degree from the galactic center. Being almost
frequency-independent, these temperature asymmetries are indicative of a
Doppler-induced effect regarding the line-of-sight dynamics on the halo scale,
the ejections from the galactic center and, possibly, even the tidal
interaction with M81 galaxy. The temperature asymmetry thus acts as a
model-independent tool to reveal the bulk dynamics in nearby edge-on spiral
galaxies, like the Sunyaev-Zeldovich effect for clusters of galaxies.Comment: 4 pages, 3 figures, in press on A&
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