67 research outputs found
A Novel Photonic Material for Designing Arbitrarily Shaped Waveguides in Two Dimensions
We investigate numerically optical properties of novel two-dimensional
photonic materials where parallel dielectric rods are randomly placed with the
restriction that the distance between rods is larger than a certain value. A
large complete photonic gap (PG) is found when rods have sufficient density and
dielectric contrast. Our result shows that neither long-range nor short-range
order is an essential prerequisite to the formation of PGs. A universal
principle is proposed for designing arbitrarily shaped waveguides, where
waveguides are fenced with side walls of periodic rods and surrounded by the
novel photonic materials. We observe highly efficient transmission of light for
various waveguides. Due to structural uniformity, the novel photonic materials
are best suited for filling up the outer region of waveguides of arbitrary
shape and dimension comparable with the wavelength.Comment: 4 figure
Oxygen diffusion of non-stoichiometric (La, Sr)MnO3 /CERIA NANO-composite SOFC cathode
Solid oxide fuel cell (SOFC) is one of the highly efficient energy generation system, and it requires higher power density per unit volume to expand SOFC stationary market as well as vehicle. Co-sintering of stacks or cells including electrodes, electrolyte and separators is most promising approach to improve the power density significantly. Generally, cathode materials have low heat resistant temperatures, and they were easily decomposed or degraded by sintering at a high temperature which is suitable for densification of SOFC electrolytes. Cathode material of (La1-xSrx)1-yMnO3 (LSM) shows relatively highly heat resistance and preferable low-reactivity with fluorite electrolytes during sintering at high temperatures. The addition of LSM also much increased degradation temperature. However, it shows lower cathodic properties than lanthanum strontium cobaltite and lanthanum strontium cobalt ferrite because of poor oxygen ionic conduction. We thus investigate LSM/ceria nanocomposite cathode materials to improve oxygen ionic conduction.
The nanocomposite precursor powder containing LSM and lanthanum doped ceria (LDC) was synthesized by glycine method. Two stoichiometric compositions, which are stoichiometric composition (y=0) and non-stoichiometric (y=0.05), were prepared as LSM, and LDCs that were dissolved with lanthanum at various ratios were used to investigate inter-diffusion of lanthanum between LSM and LDC. The composite ratio of LSM and CeO2 was fixed at 9: 1 (molar ratio). Figure 1 shows SEM image of LSM/LDC nanocomposite sintered at 1200oC for 5 h in air. Sintering at 1200oC for 5h resulted in dense composite, and fine LDC particles were homogeneously dispersed with LSM. Lanthanum ratios of LDC and LSM in the composite were identified using XRD peak shift of LDC and magnetic properties of LSM, respectively. Electrical conductivity and oxygen diffusion coefficient were estimated with these dense composites. Oxygen diffusion coefficient were obtained by electrical conductivity relaxation method.
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Direct observation of the ground state of a 1/3 quantum magnetization plateau in SrMnPO using neutron diffraction measurements
We can directly investigate the ground state in magnetization-plateau fields
(plateau ground state) using neutron diffraction measurements. We performed
neutron diffraction measurements on the spin-5/2 trimer substance
SrMnPO in magnetization-plateau fields. The integrated
intensities of magnetic reflections calculated using an expectation value of
each spin in a plateau ground state of an isolated-trimer model agree well with
those obtained experimentally in the magnetization-plateau fields. We succeeded
in direct observation of a plateau ground state in SrMnPO
Confirmation of a one-dimensional spin-1/2 Heisenberg system with ferromagnetic first-nearest-neighbor and antiferromagnetic second-nearest-neighbor interactions in RbCuMoO
We have investigated magnetic properties of RbCuMoO
powder. Temperature dependence of magnetic susceptibility and magnetic-field
dependence of magnetization have shown that this cuprate is a model compound of
a one-dimensional spin-1/2 Heisenberg system with ferromagnetic
first-nearest-neighbor (1NN) and antiferromagnetic second-nearest-neighbor
(2NN) competing interactions (competing system). Values of the 1NN and 2NN
interactions are estimated as K and K (). This value of suggests that the ground state is a
spin-singlet incommensurate state. In spite of relatively large and
, no magnetic phase transition appears down to 2 K, while an
antiferromagnetic transition occurs in other model compounds of the competing
system with ferromagnetic 1NN interaction. For that reason,
RbCuMoO is an ideal model compound to study properties of
the incommensurate ground state that are unconfirmed experimentally.Comment: 6 pages, 4 figure
Successive phase transitions to antiferromagnetic and weak-ferromagnetic long-range orders in quasi-one-dimensional antiferromagnet CuMoO
Investigation of the magnetism of CuMoO single crystal, which has
antiferromagnetic (AF) linear chains interacting with AF dimers, reveals an AF
second-order phase transition at K. Although weak
ferromagnetic-like behavior appears at lower temperatures in low magnetic
fields, complete remanent magnetization cannot be detected down to 0.5 K.
However, a jump is observed in the magnetization below weak ferromagnetic (WF)
phase transition at K when a tiny magnetic field along
the a axis is reversed, suggesting that the coercive force is very weak. A
component of magnetic moment parallel to the chain forms AF long-range order
(LRO) below , while a perpendicular component is disordered above
at zero magnetic field and forms WF-LRO below .
Moreover, the WF-LRO is also realized with applying magnetic fields even
between and . These results are explainable by both
magnetic frustration among symmetric exchange interactions and competition
between symmetric and asymmetric Dzyaloshinskii-Moriya exchange interactions.Comment: 7 pages, 7 figure
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