15,637 research outputs found
Room-Temperature Ferrimagnet with Frustrated Antiferroelectricity: Promising Candidate Toward Multiple State Memory
On the basis of first-principles calculations we show that the M-type
hexaferrite BaFe12O19 exhibits frustrated antiferroelectricity associated with
its trigonal bipyramidal Fe3+ sites. The ferroelectric (FE) state of BaFe12O19,
reachable by applying an external electric field to the antiferroelectric (AFE)
state, can be made stable at room temperature by appropriate element
substitution or strain engineering. Thus M-type hexaferrite, as a new type of
multiferoic with coexistence of antiferroelectricity and ferrimagnetism,
provide a basis for studying the phenomenon of frustrated antiferroelectricity
and realizing multiple state memory devices.Comment: supporting material available via email. arXiv admin note: text
overlap with arXiv:1210.7116 by other author
Evolution of Intermediate-Mass Black Hole X-Ray Binaries
The majority of the ultraluminous X-ray sources (ULXs) in external galaxies
are believed to be accreting black holes in binary systems; some of the black
holes could be as massive as \sim 100-1000 \ms. We have performed evolution
calculations for intermediate-mass black hole X-ray binaries, assuming they are
formed in dense star clusters via tidal capture. The results are compared with
those for stellar-mass black holes X-ray binaries. We find that these two types
of black holes may have similar companion stars and binary orbits if observed
as ULXs. However, intermediate-mass black holes seem to be favored in
explaining the most luminous ULXs. We also discuss the possibilities of
transient behavior and beamed emission in the evolution of these binary
systems.Comment: 11 pages, 3 figures. Accepted for publication in ApJ
Cooperative Effect of Electron Correlation and Spin-Orbit Coupling on the Electronic and Magnetic Properties of Ba2NaOsO6
The electronic and magnetic properties of the cubic double perovskite
Ba2NaOsO6 were examined by performing first-principles density functional
theory calculations and analyzing spin-orbit coupled states of an Os7+ (d1) ion
at an octahedral crystal field. The insulating behavior of Ba2NaOsO6 was shown
to originate from a cooperative effect of electron correlation and spin-orbit
coupling. This cooperative effect is responsible not only for the absence of
orbital ordering in Ba2 NaOsO6 but also for a small magnetic moment and a weak
magnetic anisotropy in Ba2NaOsO6
Optimizing Hartree-Fock orbitals by the density-matrix renormalization group
We have proposed a density-matrix renormalization group (DMRG) scheme to
optimize the one-electron basis states of molecules. It improves significantly
the accuracy and efficiency of the DMRG in the study of quantum chemistry or
other many-fermion system with nonlocal interactions. For a water molecule, we
find that the ground state energy obtained by the DMRG with only 61 optimized
orbitals already reaches the accuracy of best quantum Monte Carlo calculation
with 92 orbitals.Comment: published version, 4 pages, 4 figure
Quantum transfer matrix method for one-dimensional disordered electronic systems
We develop a novel quantum transfer matrix method to study thermodynamic
properties of one-dimensional (1D) disordered electronic systems. It is shown
that the partition function can be expressed as a product of local
transfer matrices. We demonstrate this method by applying it to the 1D
disordered Anderson model. Thermodynamic quantities of this model are
calculated and discussed.Comment: 7 pages, 10 figure
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