1,208 research outputs found
Perovskite Manganites Hosting Versatile Multiferroic Phases with Symmetric and Antisymmetric Exchange Strictions
Complete magnetoelectric (ME) phase diagrams of orthorhombic MnO
with and without magnetic moments on the ions have been established. Three
kinds of multiferroic ground states, the -cycloidal, the -cycloidal,
and the collinear -type phases, have been identified by the distinct ME
responses. The electric polarization of the -type phase dominated by the
symmetric spin exchange () is more than 10 times as
large as that of the -cycloidal phase dominated by the antisymmetric one
(), and the ME response is enhanced near the
bicritical phase boundary between these multiferroic phases of different
origins. These findings will provide an important clue for the development of
the magnetically induced multiferroics.Comment: 5 pages, 3 figure
Syntheses of 18F-5-Fluorouracil, 18F-Fluorouridine and 18F-5-Fluoro-2\u27-deoxyuridine
開始ページ、終了ページ: 冊子体のページ付
Right-Handed Sneutrino as Cold Dark Matter
We consider supersymmetric models with right-handed neutrinos where neutrino
masses are purely Dirac-type. In this model, right-handed sneutrino can be the
lightest supersymmetric particle and can be a viable candidate of cold dark
matter of the universe. Right-handed sneutrinos are never thermalized in the
early universe because of weakness of Yukawa interaction, but are effectively
produced by decays of various superparticles. We show that the present mass
density of right-handed sneutrino can be consistent with the observed dark
matter density.Comment: 4 pages, 1 figur
Higgs Properties and Fourth Generation Leptons
It is possible that there are additional vector-like generations where the
quarks have mass terms that do not originate from weak symmetry breaking, but
the leptons only get mass through weak symmetry breaking. We discuss the impact
that the new leptons have on Higgs boson decay branching ratios and on the
range of allowed Higgs masses in such a model (with a single new vector-like
generation). We find that if the fourth generation leptons are too heavy to be
produced in Higgs decay, then the new leptons reduce the branching ratio for h
-> gamma gamma to about 30% of its standard-model value. The dependence of this
branching ratio on the new charged lepton masses is weak. Furthermore the
expected Higgs production rate at the LHC is very near its standard-model value
if the new quarks are much heavier than the weak scale. If the new quarks have
masses near the cutoff for the theory then for cutoffs greater than 10^15 GeV,
the new lepton masses cannot be much heavier than about 100 GeV and the Higgs
mass must have a value around 175 GeV.Comment: 8 pages, 8 figures, published versio
Magnetic-field induced competition of two multiferroic orders in a triangular-lattice helimagnet MnI2
Magnetic and dielectric properties with varying magnitude and direction of
magnetic field H have been investigated for a triangular lattice helimagnet
MnI2. The in-plane electric polarization P emerges in the proper screw magnetic
ground state below 3.5 K, showing the rearrangement of six possible
multiferroic domains as controlled by the in-plane H. With every 60-degree
rotation of H around the [001]-axis, discontinuous 120-degree flop of P-vector
is observed as a result of the flop of magnetic modulation vector q. With
increasing the in-plane H above 3 T, however, the stable q-direction changes
from q|| to q||, leading to a change of P-flop patterns under
rotating H. At the critical field region (~3 T), due to the phase competition
and resultant enhanced q-flexibility, P-vector smoothly rotates clockwise twice
while H-vector rotates counter-clockwise once.Comment: 4 pages, 3 figures. Accepted in Physical Review Letter
Observation of Devil's Staircase in the Novel Spin Valve System SrCoO
Using resonant soft x-ray scattering as a function of both temperature and
magnetic field, we reveal a large number of almost degenerate magnetic orders
in SrCo6O11. The Ising-like spins in this frustrated material in fact exhibit a
so-called magnetic devil's staircase. It is demonstrated how a magnetic field
induces transitions between different microscopic spin configurations, which is
responsible for the magnetoresistance of SrCo6O11. This material therefore
constitutes a unique combination of a magnetic devil's staircase and spin valve
effects, yielding a novel type of magnetoresistance system.Comment: 5 pages, 5 figure
Increased Amounts of D-Enantiomer Dependent on Alkaline Concentration in the Synthesis of L-[methyl-11C] Methionine
開始ページ、終了ページ: 冊子体のページ付
Cupric chloride CuCl2 as an S=1/2 chain multiferroic
Magnetoelectric properties were investigated for an S=1/2 chain
antiferromagnet CuCl2, which turns out to be the first example of non-chalcogen
based spiral-spin induced multiferroics. Upon the onset of helimagnetic order
propagating along the b-axis under zero magnetic field (H), we found emergence
of ferroelectric polarization along the c-axis. Application of H along the
b-axis leads to spin-flop transition coupled with drastic suppression of
ferroelectricity, and rotation of H around the b-axis induces the rotation of
spin-spiral plane and associated polarization direction. These behaviors are
explained well within the framework of the inverse Dzyaloshinskii-Moriya model,
suggesting the robustness of this magnetoelectric coupling mechanism even under
the strong quantum fluctuation.Comment: 5 pages, 5 figure
Two-Staged Magnetoresistance Driven by Ising-like Spin Sublattice in SrCo6O11
A two-staged, uniaxial magnetoresistive effect has been discovered in
SrCo6O11 having a layered hexagonal structure. Conduction electrons and
localized Ising spins are in different sublattices but their interpenetration
makes the conduction electrons sensitively pick up the stepwise
field-dependence of magnetization. The stepwise field-dependence suggests two
competitive interlayer interactions between ferromagnetic Ising-spin layers,
i.e., a ferromagnetic nearest-layer interaction and an antiferromagnetic
next-nearest-layer interaction. This oxide offers a unique opportunity to study
nontrivial interplay between conduction electrons and Ising spins, the coupling
of which can be finely controlled by a magnetic field of a few Tesla.Comment: 14 pages, 4 figures, accepted for publication in Phys. Rev. Let
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