3,617 research outputs found
Lattice Distortion and Magnetism of 3d- Perovskite Oxides
Several puzzling aspects of interplay of the experimental lattice distortion
and the the magnetic properties of four narrow -band perovskite oxides
(YTiO, LaTiO, YVO, and LaVO) are clarified using results of
first-principles electronic structure calculations. First, we derive parameters
of the effective Hubbard-type Hamiltonian for the isolated bands using
newly developed downfolding method for the kinetic-energy part and a hybrid
approach, based on the combination of the random-phase approximation and the
constraint local-density approximation, for the screened Coulomb interaction
part. Then, we solve the obtained Hamiltonian using a number of techniques,
including the mean-field Hartree-Fock (HF) approximation, the second-order
perturbation theory for the correlation energy, and a variational superexchange
theory. Even though the crystal-field splitting is not particularly large to
quench the orbital degrees of freedom, the crystal distortion imposes a severe
constraint on the form of the possible orbital states, which favor the
formation of the experimentally observed magnetic structures in YTiO,
YVO_, and LaVO even at the HF level. Beyond the HF approximation, the
correlations effects systematically improve the agreement with the experimental
data. Using the same type of approximations we could not reproduce the correct
magnetic ground state of LaTiO. However, we expect that the situation may
change by systematically improving the level of approximations for dealing with
the correlation effects.Comment: 30 pages, 17 figures, 8 tables, high-quality figures are available
via e-mai
Realization of anisotropic compass model on the diamond lattice of Cu in CuAlO
Spin-orbit (SO) Mott insulators are regarded as a new paradigm of magnetic
materials, whose properties are largely influenced by SO coupling and featured
by highly anisotropic bond-dependent exchange interactions between the
spin-orbital entangled Kramers doublets, as typically manifested in
iridates. Here, we propose that a very similar situation can be realized in
cuprates when the Cu ions reside in a tetrahedral environment, like in
spinel compounds. Using first-principles electronic structure calculations, we
construct a realistic model for the diamond lattice of the Cu ions in
CuAlO and show that the magnetic properties of this compound are
largely controlled by anisotropic compass-type exchange interactions that
dramatically modify the magnetic ground state by lifting the spiral spin-liquid
degeneracy and stabilizing a commensurate single- spiral
Hybridization and spin-orbit coupling effects in quasi-one-dimensional spin-1/2 magnet Ba3Cu3Sc4O12
We study electronic and magnetic properties of the quasi-one-dimensional
spin-1/2 magnet Ba3Cu3Sc4O12 with a distinct orthogonal connectivity of CuO4
plaquettes. An effective low-energy model taking into account spin-orbit
coupling was constructed by means of first-principles calculations. On this
basis a complete microscopic magnetic model of Ba3Cu3Sc4O12, including
symmetric and antisymmetric anisotropic exchange interactions, is derived. The
anisotropic exchanges are obtained from a distinct first-principles numerical
scheme combining, on one hand, the local density approximation taking into
account spin-orbit coupling, and, on the other hand, projection procedure along
with the microscopic theory by Toru Moriya. The resulting tensors of the
symmetric anisotropy favor collinear magnetic order along the structural chains
with the leading ferromagnetic coupling J1 = -9.88 meV. The interchain
interactions J8 = 0.21 meV and J5 = 0.093 meV are antiferromagnetic. Quantum
Monte Carlo simulations demonstrated that the proposed model reproduces the
experimental Neel temperature, magnetization and magnetic susceptibility data.
The modeling of neutron diffraction data reveals an important role of the
covalent Cu-O bonding in Ba3Cu3Sc4O12.Comment: 11 pages, 12 figure
Low-Temperature Spin Dynamics of Doped Manganites: roles of Mn-t2g and eg and O-2p states
The low-temperature spin dynamics of doped manganites have been analyzed
within a tight-binding model, the parameters of which are estimated by mapping
the results of ab initio density functional calculations onto the model. This
approach is found to provide a good description of the spin dynamics of the
doped manganites, observed earlier within the ab initio calculations. Our
analysis not only provides some insight into the roles of the eg and the t2g
states but also indicates that the oxygen p states play an important role in
the spin dynamics. This may cast doubt on the adaptability of the conventional
model Hamiltonian approaches to the analysis of spin dynamics of doped
manganites.Comment: 12 pages; Includes 5 figure
Ferromagnetic zigzag chains and properties of the charge ordered perovskite manganites
The low-temperature properties of the so-called ''charge ordered'' state in
50% doped perovskite manganites are described from the viewpoint of the
magnetic spin ordering. In these systems, the zigzag antiferromagnetic
ordering, combined with the double-exchange physics, effectively divides the
whole sample into the one-dimensional ferromagnetic zigzag chains and results
in the anisotropy of electronic properties. The electronic structure of one
such chain is described by an effective 33 Hamiltonian in the basis of
Mn() orbitals. We treat this problem analytically and consider the
following properties: (i) the nearest-neighbor magnetic interactions; (ii) the
distribution of the Mn() and Mn() states near the Fermi level, and
their contribution to the optical conductivity and the resonant x-ray
scattering near the Mn -absorption edge. We argue that the anisotropy of
magnetic interactions in the double-exchange limit, combined with the isotropic
superexchange interactions, readily explains both the local and the global
stability of the zigzag antiferromagnetic state. The two-fold degeneracy of
levels plays a very important role in the problem and explains the
insulating behavior of the zigzag chain, as well as the appearance of the
orbital ordering in the double-exchange model. Importantly, however, the charge
ordering itself is expected to play only a minor role and is incompatible with
the ferromagnetic coupling within the chain. We also discuss possible effects
of the Jahn-Teller distortion and compare the tight-binding picture with
results of band structure calculations in the local-spin-density approximation.Comment: 35 pages, 8 figure
Half-magnetization plateaux in Cr spinels
Magnetization plateaux, visible as anomalies in magnetic susceptibility at
low temperatures, are one of the hallmarks of frustrated magnetism. An
extremely robust half-magnetization plateau is observed in the spinel oxides
CdCr2O4 and HgCr2O4, where it is accompanied by a substantial lattice
distortion. We give an overview of the present state experiment for CdCr2O4 and
HgCr2O4, and show how such a half-magnetization plateau arises quite naturally
in a simple model of these systems, once coupling to the lattice is taken into
account.Comment: 8 pages latex using IOP macros, from review talk given at RHMF 2006
(Sendai
Origin of the giant magnetic moments of Fe impurities on and in Cs films
To explore the origin of the observed giant magnetic moments ()
of Fe impurities on the surface and in the bulk of Cs films, we have performed
the relativistic LSDA + U calculations using the linearized muffin-tin orbital
(LMTO) band method. We have found that Fe impurities in Cs behave differently
from those in noble metals or in Pd. Whereas the induced spin polarization of
Cs atoms is negligible, the Fe ion itself is found to be the source of the
giant magnetic moment. The 3d electrons of Fe in Cs are localized as the 4f
electrons in rare-earth ions so that the orbital magnetic moment becomes as
large as the spin magnetic moment. The calculated total magnetic moment of , which comes mainly from Fe ion, is close to the experimentally
observed value.Comment: 4 pages including 3 figures and 1 table. Submitted to PR
ΠΠ΅ΠΎΠ±ΡΡΠ½ΡΠΉ ΡΠ»ΡΡΠ°ΠΉ Π»Π΅ΡΠ΅Π½ΠΈΡ ΠΏΠ°ΡΠΈΠ΅Π½ΡΠ° Ρ Ρ ΠΈΠΌΠΈΡΠ΅ΡΠΊΠΈΠΌ ΠΎΠΆΠΎΠ³ΠΎΠΌ ΠΏΠΈΡΠ΅Π²ΠΎΠ΄Π° ΠΈ ΠΏΠ΅ΡΡΠΎΡΠ°ΡΠΈΠ΅ΠΉ ΠΆΠ΅Π»ΡΠ΄ΠΊΠ°
Treatment of patients with chemical burns of the esophagus and stomach is a difficult task.Perforation of the stomach or the formation of strictures of the esophagus, stomach, duodenum, and even the initial parts of the jejunum can be the outcome of chemical burns.Patients with concomitant esophageal and gastric strictures are the most difficult to treat, which often requires multi-stage operations.This article describes a clinical case of surgical treatment of a patient with a combined chemical burn of the esophagus and stomach with hydrochloric acid. One week after hospitalization, the patient had gastric perforation. The patient was urgently operated in the course of peritonitis. The peculiarity of the operation was that the surgeons, having made a gastrectomy, removed the esophageal stump to the anterior abdominal wall in the epigastrium and applied an enterostomy. In such a state with significant alimentary depletion (body mass index β BMI 15) on 11.10.02 the patient was taken to a Moscow clinic. A year later, the main surgical reconstructive treatment was performed β retrosternal bypass esophagoplasty of the right half of the large intestine and the terminal ileum in the isoperistaltic position, as well as extirpation of the esophagus. As a result of long-term treatment and several surgical interventions, a good short-term and long-term result was obtained.Β ΠΠ΅ΡΠ΅Π½ΠΈΠ΅ Π±ΠΎΠ»ΡΠ½ΡΡ
Ρ Ρ
ΠΈΠΌΠΈΡΠ΅ΡΠΊΠΈΠΌΠΈ ΠΎΠΆΠΎΠ³Π°ΠΌΠΈ ΠΏΠΈΡΠ΅Π²ΠΎΠ΄Π° ΠΈ ΠΆΠ΅Π»ΡΠ΄ΠΊΠ° ΠΏΡΠ΅Π΄ΡΡΠ°Π²Π»ΡΠ΅Ρ ΡΠ»ΠΎΠΆΠ½ΡΡ Π·Π°Π΄Π°ΡΡ. ΠΡΡ
ΠΎΠ΄ΠΎΠΌ Ρ
ΠΈΠΌΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΎΠΆΠΎΠ³ΠΎΠ² ΠΌΠΎΠΆΠ΅Ρ Π±ΡΡΡ ΠΏΠ΅ΡΡΠΎΡΠ°ΡΠΈΡ ΠΆΠ΅Π»ΡΠ΄ΠΊΠ° ΠΈΠ»ΠΈ ΡΠΎΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅ ΡΡΡΠΈΠΊΡΡΡ ΠΏΠΈΡΠ΅Π²ΠΎΠ΄Π°, ΠΆΠ΅Π»ΡΠ΄ΠΊΠ°, Π΄Π²Π΅Π½Π°Π΄ΡΠ°ΡΠΈΠΏΠ΅ΡΡΡΠ½ΠΎΠΉ ΠΈ Π΄Π°ΠΆΠ΅ Π½Π°ΡΠ°Π»ΡΠ½ΡΡ
ΠΎΡΠ΄Π΅Π»ΠΎΠ² ΡΠΎΡΠ΅ΠΉ ΠΊΠΈΡΠΊΠΈ.ΠΠΎΠ»ΡΠ½ΡΠ΅ Ρ ΡΠΎΡΠ΅ΡΠ°Π½Π½ΡΠΌΠΈ ΠΎΠΆΠΎΠ³ΠΎΠ²ΡΠΌΠΈ ΡΡΡΠΈΠΊΡΡΡΠ°ΠΌΠΈ ΠΏΠΈΡΠ΅Π²ΠΎΠ΄Π° ΠΈ ΠΆΠ΅Π»ΡΠ΄ΠΊΠ° ΡΠ²Π»ΡΡΡΡΡ Π½Π°ΠΈΠ±ΠΎΠ»Π΅Π΅ ΡΠ»ΠΎΠΆΠ½ΡΠΌΠΈ Π΄Π»Ρ Π»Π΅ΡΠ΅Π½ΠΈΡ, ΠΊΠΎΡΠΎΡΠΎΠ΅ ΡΠ°ΡΡΠΎ ΡΡΠ΅Π±ΡΠ΅Ρ ΠΌΠ½ΠΎΠ³ΠΎΡΡΠ°ΠΏΠ½ΡΡ
ΠΎΠΏΠ΅ΡΠ°ΡΠΈΠΉ.Π Π΄Π°Π½Π½ΠΎΠΉ ΡΠ°Π±ΠΎΡΠ΅ ΠΎΠΏΠΈΡΠ°Π½ ΠΊΠ»ΠΈΠ½ΠΈΡΠ΅ΡΠΊΠΈΠΉ ΡΠ»ΡΡΠ°ΠΉ Ρ
ΠΈΡΡΡΠ³ΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ Π»Π΅ΡΠ΅Π½ΠΈΡ ΠΏΠ°ΡΠΈΠ΅Π½ΡΠ° Ρ ΡΠΎΡΠ΅ΡΠ°Π½Π½ΡΠΌ Ρ
ΠΈΠΌΠΈΡΠ΅ΡΠΊΠΈΠΌ ΠΎΠΆΠΎΠ³ΠΎΠΌ ΠΏΠΈΡΠ΅Π²ΠΎΠ΄Π° ΠΈ ΠΆΠ΅Π»ΡΠ΄ΠΊΠ° ΡΠΎΠ»ΡΠ½ΠΎΠΉ ΠΊΠΈΡΠ»ΠΎΡΠΎΠΉ. Π§Π΅ΡΠ΅Π· Π½Π΅Π΄Π΅Π»Ρ ΠΏΠΎΡΠ»Π΅ Π³ΠΎΡΠΏΠΈΡΠ°Π»ΠΈΠ·Π°ΡΠΈΠΈ ΠΏΡΠΎΠΈΠ·ΠΎΡΠ»Π° ΠΏΠ΅ΡΡΠΎΡΠ°ΡΠΈΡ ΠΆΠ΅Π»ΡΠ΄ΠΊΠ°. ΠΠ°ΡΠΈΠ΅Π½Ρ Π±ΡΠ» ΡΠΊΡΡΡΠ΅Π½Π½ΠΎ ΠΎΠΏΠ΅ΡΠΈΡΠΎΠ²Π°Π½ Π½Π° ΡΠΎΠ½Π΅ ΠΏΠ΅ΡΠΈΡΠΎΠ½ΠΈΡΠ°. ΠΡΠΎΠ±Π΅Π½Π½ΠΎΡΡΡ ΠΎΠΏΠ΅ΡΠ°ΡΠΈΠΈ Π·Π°ΠΊΠ»ΡΡΠ°Π»Π°ΡΡ Π² ΡΠΎΠΌ, ΡΡΠΎ Ρ
ΠΈΡΡΡΠ³ΠΈ, ΡΠ΄Π΅Π»Π°Π² Π³Π°ΡΡΡΡΠΊΡΠΎΠΌΠΈΡ, Π²ΡΠ²Π΅Π»ΠΈ ΠΊΡΠ»ΡΡΡ ΠΏΠΈΡΠ΅Π²ΠΎΠ΄Π° Π½Π° ΠΏΠ΅ΡΠ΅Π΄Π½ΡΡ Π±ΡΡΡΠ½ΡΡ ΡΡΠ΅Π½ΠΊΡ Π² ΡΠΏΠΈΠ³Π°ΡΡΡΠΈΠΈ ΠΈ Π½Π°Π»ΠΎΠΆΠΈΠ»ΠΈ ΡΠ½ΡΠ΅ΡΠΎΡΡΠΎΠΌΡ. Π ΡΠ°ΠΊΠΎΠΌ ΡΠΎΡΡΠΎΡΠ½ΠΈΠΈ Ρ Π²ΡΡΠ°ΠΆΠ΅Π½Π½ΡΠΌ Π°Π»ΠΈΠΌΠ΅Π½ΡΠ°ΡΠ½ΡΠΌ ΠΈΡΡΠΎΡΠ΅Π½ΠΈΠ΅ΠΌ (ΠΈΠ½Π΄Π΅ΠΊΡ ΠΌΠ°ΡΡΡ ΡΠ΅Π»Π° (ΠΠΠ’) β 15) 11.10.2002 Π±ΠΎΠ»ΡΠ½ΠΎΠΉ Π±ΡΠ» Π΄ΠΎΡΡΠ°Π²Π»Π΅Π½ Π² ΠΌΠΎΡΠΊΠΎΠ²ΡΠΊΡΡ ΠΊΠ»ΠΈΠ½ΠΈΠΊΡ. Π ΠΊΠ°ΡΠ΅ΡΡΠ²Π΅ ΠΎΡΠ½ΠΎΠ²Π½ΠΎΠ³ΠΎ Ρ
ΠΈΡΡΡΠ³ΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ Π»Π΅ΡΠ΅Π½ΠΈΡ (ΡΠΏΡΡΡΡ 1 Π³ΠΎΠ΄) Π±ΡΠ»Π° Π²ΡΠΏΠΎΠ»Π½Π΅Π½Π° ΡΠ΅ΠΊΠΎΠ½ΡΡΡΡΠΊΡΠΈΠ²Π½Π°Ρ ΠΎΠΏΠ΅ΡΠ°ΡΠΈΡ β Π·Π°Π³ΡΡΠ΄ΠΈΠ½Π½Π°Ρ ΡΡΠ½ΡΠΈΡΡΡΡΠ°Ρ ΡΠ·ΠΎΡΠ°Π³ΠΎΠΏΠ»Π°ΡΡΠΈΠΊΠ° ΠΏΡΠ°Π²ΠΎΠΉ ΠΏΠΎΠ»ΠΎΠ²ΠΈΠ½ΠΎΠΉ ΡΠΎΠ»ΡΡΠΎΠΉ ΠΊΠΈΡΠΊΠΈ ΠΈ ΡΠ΅ΡΠΌΠΈΠ½Π°Π»ΡΠ½ΡΠΌ ΠΎΡΠ΄Π΅Π»ΠΎΠΌ ΠΏΠΎΠ΄Π²Π·Π΄ΠΎΡΠ½ΠΎΠΉ ΠΊΠΈΡΠΊΠΈ Π² ΠΈΠ·ΠΎΠΏΠ΅ΡΠΈΡΡΠ°Π»ΡΡΠΈΡΠ΅ΡΠΊΠΎΠΉ ΠΏΠΎΠ·ΠΈΡΠΈΠΈ, Π° ΡΠ°ΠΊΠΆΠ΅ ΡΠΊΡΡΠΈΡΠΏΠ°ΡΠΈΡ ΠΏΠΈΡΠ΅Π²ΠΎΠ΄Π°. Π ΡΠ΅Π·ΡΠ»ΡΡΠ°ΡΠ΅ Π΄Π»ΠΈΡΠ΅Π»ΡΠ½ΠΎΠ³ΠΎ Π»Π΅ΡΠ΅Π½ΠΈΡ ΠΈ Π½Π΅ΡΠΊΠΎΠ»ΡΠΊΠΈΡ
ΠΎΠΏΠ΅ΡΠ°ΡΠΈΠ²Π½ΡΡ
Π²ΠΌΠ΅ΡΠ°ΡΠ΅Π»ΡΡΡΠ² Π±ΡΠ»ΠΈ ΠΏΠΎΠ»ΡΡΠ΅Π½Ρ Ρ
ΠΎΡΠΎΡΠΈΠ΅ ΡΠ΅Π·ΡΠ»ΡΡΠ°ΡΡ Π² Π±Π»ΠΈΠΆΠ°ΠΉΡΠ΅ΠΌ ΠΈ ΠΎΡΠ΄Π°Π»Π΅Π½Π½ΠΎΠΌ ΠΏΠ΅ΡΠΈΠΎΠ΄Π°Ρ
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