346 research outputs found
Coexistence of long-ranged charge and orbital order and spin-glass state in single-layered manganites with weak quenched disorder
The relationship between orbital and spin degrees of freedom in the
single-crystals of the hole-doped PrCaMnO, 0.3
0.7, has been investigated by means of ac-magnetometry and charge
transport. Even though there is no cation ordering on the -site, the
quenched disorder is extremely weak in this system due to the very similar
ionic size of Pr and Ca. A clear asymmetric response of the
system to the under- (respective over-) hole doping was observed. The
long-ranged charge-orbital order established for half doping (=0.5) subsists
in the over-doping case ( 0.5), albeit rearranged to accommodate the
extra holes introduced in the structure. The charge-orbital order is however
destabilized by the presence of extra localized electrons (under-doping,
0.5), leading to its disappearance below =0.35. We show that in an
intermediate under-doped region, with 0.35 0.5, the
``orbital-master spin-slave'' relationship commonly observed in half-doped
manganites does not take place. The long-ranged charge-orbital order is not
accompanied by an antiferromagnetic transition at low temperatures, but by a
frustrated short-ranged magnetic state bringing forth a spin-glass phase. We
discuss in detail the nature and origin of this spin-glass state, which, as in
the half-doped manganites with large quenched disorder, is not related to the
macroscopic phase separation observed in crystals with minor defects or
impurities.Comment: EPL style; 6 pages, 5 figure
Magnetic phase diagram of doped CMR manganites
The magnetic phase diagram of the colossal magnetoresistance (CMR) manganites
is determined based on the Hamiltonian incorporating the double-exchange (DE)
interaction between degenerate Mn orbitals and the antiferromagnetic (AF)
superexchange interaction between Mn spins. We have employed the
rigorous quantum mechanical formalism and obtained the finite temperature phase
diagram which describes well the commonly observed features in CMR manganites.
We have also shown that the CE-type AF structure cannot be stabilized at
=0.5 in this model.Comment: 2 pages, 1 figure; Transport and Thermal Properties of Advanced
Materials(Aug. 2002; Hiroshima, Japan
Real-space observation of short-period cubic lattice of skyrmions in MnGe
Emergent phenomena and functions arising from topological electron-spin
textures in real space or momentum space are attracting growing interest for
new concept of states of matter as well as for possible applications to
spintronics. One such example is a magnetic skyrmion, a topologically stable
nanoscale spin vortex structure characterized by a topological index.
Real-space regular arrays of skyrmions are described by combination of
multi-directional spin helixes. Nanoscale configurations and characteristics of
the two-dimensional skyrmion hexagonal-lattice have been revealed extensively
by real-space observations. Other three-dimensional forms of skyrmion lattices,
such as a cubic-lattice of skyrmions, are also anticipated to exist, yet their
direct observations remain elusive. Here we report real-space observations of
spin configurations of the skyrmion cubic-lattice in MnGe with a very short
period (~3 nm) and hence endowed with the largest skyrmion number density. The
skyrmion lattices parallel to the {100} atomic lattices are directly observed
using Lorentz transmission electron microscopes (Lorentz TEMs). It enables the
first simultaneous observation of magnetic skyrmions and underlying
atomic-lattice fringes. These results indicate the emergence of
skyrmion-antiskyrmion lattice in MnGe, which is a source of emergent
electromagnetic responses and will open a possibility of controlling
few-nanometer scale skyrmion lattices through atomic lattice modulations
Spin-polarized electric currents in quantum transport through tubular two-dimensional electron gases
Scattering theory is employed to derive a Landauer-type formula for the spin
and the charge currents, through a finite region where spin-orbit interactions
are effective. It is shown that the transmission matrix yields the spatial
direction and the magnitude of the spin polarization. This formula is used to
study the currents through a tubular two-dimensional electron gas. In this
cylindrical geometry, which may be realized in experiment, the transverse
conduction channels are not mixed (provided that the spin-orbit coupling is
uniform). It is then found that for modest boundary scattering, each step in
the quantized conductance is split into two, and the new steps have a non-zero
spin conductance, with the spin polarization perpendicular to the direction of
the current.Comment: 6 pages, 5 figure
Dimensionality dependence of optical nonlinearity and relaxation dynamics in cuprates
Femtosecond pump-probe measurements find pronounced dimensionality dependence
of the optical nonlinearity in cuprates. Although the coherent two-photon
absorption (TPA) and linear absorption bands nearly overlap in both quasi-one
and two-dimensional (1D and 2D) cuprates, the TPA coefficient is one order of
magnitude smaller in 2D than in 1D. Furthermore, picosecond recovery of optical
transparency is observed in 1D cuprates, while the recovery in 2D involves
relaxation channels with a time scales of tens of picoseconds. The experimental
results are interpreted within the two-band extended Hubbard model.Comment: 10 pages, 4 figure
Pd-catalysed, Ag-assisted C2-H alkenylation of benzophospholes
A palladium-catalysed, silver-assisted regioselective C2-H alkenylation of benzophospholes with terminal alkenes has been developed. The palladium catalysis accommodates styrenes and electron-deficient alkenes including ester, ketone, nitrile, and phosphonate. Thus, this protocol enables the rapid construction of various benzophosphole-vinylene conjugations from the two simple C-H starting substrates. Optical properties of newly synthesized C2-alkenylated benzophospholes are also investigated.Tokura Y., Xu S., Kojima Y., et al. Pd-catalysed, Ag-assisted C2-H alkenylation of benzophospholes. Chemical Communications 58, 12208 (2022); https://doi.org/10.1039/D2CC04942B
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