157 research outputs found
Whirling spin order in the quasicrystal approximant AuAlTb
Neutron powder diffraction experiment has been performed on the quasicrystal
approximant AuAlTb, a body-center-cubic crystal of
icosahedral spin clusters. The long-range antiferromagnetic order was confirmed
at the transition temperature K. The magnetic structure
consists of noncoplanar whirling spins on the icosahedral clusters, arranging
antiferroic-manner. A simple icosahedral spin-cluster model with uniaxial
anisotropy accounts well the whirling spin order as well as the in-field
metamagnetic transition, indicating that the icosahedral symmetry is essential.Comment: 6 pages, 4 figure
Revisit of magnetic orders in 1/1 approximant crystals of Tsai-type quasicrystal from theoretical points of view
The various magnetic orders observed in approximant crystals of Tsai-type
quasicrystal are important for deepening our understanding of mysterious
magnetism in quasicrystals. Using an icosahedral cluster model with
inter-cluster interactions, we give an intuitive explanation of the mechanism
of magnetic orders previously reported by classical Monte-Carlo simulations for
an approximant-crystal model describing a Gd-based Tsai-type 1/1 approximant
crystal.Comment: 2 pages, 2 figure
Structural Modification and Metamagnetic Anomaly in the Ordered State of CeOs2Al10
A caged compound CeOs2Al10, crystallizing in the orthorhombic YbFe2Al10-type
structure, undergoes a mysterious phase transition at T_0=29 K. We report the
results of electron diffraction, magnetization, and magnetoresistance for
single crystals. Superlattice reflections characterized by a wave vector q =
(0, -2/3, 2/3) observed at 15 K indicate a structural modification in the
ordered state. Activation-type behavior of the electrical resistivity along the
three principal axes below 50 K suggests gap opening in the conduction band.
The magnetic susceptibility \chi = M/B is highly anisotropic,
\chi_a>\chi_c>\chi_b, all of which sharply decrease on cooling below T_0.
Furthermore, a metamagnetic anomaly in the magnetization and a step in the
magnetoresistance occur at B=6-8 T only when the magnetic field is applied
parallel to the orthorhombic c axis. However, T_0 hardly changes under magnetic
fields up to 14 T, irrespective of the field direction. By using these data, we
present a B-T phase diagram and discuss several scenarios for the mysterious
transition.Comment: 6 pages, 7 figures, accepted for publication in Phys. Rev.
Critical behavior and magnetocaloric effect in Tsai-type 2/1 and 1/1 quasicrystal approximants
Stable Tsai-type quinary 1/1 and 2/1 approximant crystals (ACs) with chemical
compositions Au56.25Al10Cu7In13Tb13.75 and Au55.5Al10Cu7In13Tb14.5,
respectively, exhibiting ferromagnetic (FM) long-range orders were successfully
synthesized and studied for their magnetic properties and magnetocaloric
effect. The 1/1 and 2/1 ACs primarily differ in their long-range atomic
arrangement and rare earth (RE) distribution, with the latter approaching
quasiperiodic order while still preserving periodicity. Analyses based on the
scaling principle and Kouvel-Fisher (KF) relations suggested mean-field-like
behavior near Curie temperatures in both compounds. From magnetization
measurements and the Maxwell equation, a magnetic entropy change of -4.3 and
-4.1 J/K mol Tb were derived under a magnetic field change of 7 T for the 1/1
and 2/1 ACs, respectively. The results indicated a prominent role of
intra-cluster magnetic interactions on critical behavior and magnetic entropy
of the Tsai-type compounds
Investigation of laparoscopic therapy in 56 cases of duodenal ulcer perforation
Background: Although conservative therapy has been acceptable as the first-line therapy for duodenal ulcer (DU) perforations, surgical therapies are known to have certain advantages. We investigated the indications for laparoscopic (LS) or open surgery (OS) or conservative therapy (CoT) among 56 DU perforation cases over 5 years. Methods: 31 LSs, 22 OSs and 5 CoTs were analyzed for patient's physical and surgical factors and clinical course. Results: Mean age was 51.6. Male/female ratio was 49/9. Survival ratio was 98%. Although the hospital stay (10.9 vs 19.5 days) and analgesic administrations (1.9 vs 4.6 days) were significantly shorter in LS than OS, almost all OS patients were in serious condition as evidenced by longer waiting time before treatment, stronger pain, bigger hole of perforation, more ascites accumulation and higher morbidity of complications. Two cases of multisurgery were experienced in both LS and OS groups due to leakage of seam, abscess formation, relapsed ulcer or idiopathic intestinal perforation. LS is a therapy more widely usable and more beneficial than the other two. Conclusion: LS, a minimally invasive surgery for DU perforation, should be considered as a first-line standard therapy because of significant advantages such as shorter hospital stay. OS or CoT may be selected when appropriate
Near-Infrared Spectroscopy of the Cool Brown Dwarf, SDSS 1624+00
Using the Subaru Telescope, we have obtained multiple near-infrared spectra
of the cool brown dwarf, SDSS 1624+00, in search of spectral variability in an
80 minute time span. We have found the suspected variability of water vapor
absorption throughout the observations, which requires confirmation by a longer
time baseline. After coadding the spectra, we have obtained a high-quality
spectrum covering 1.05 to 1.8 um. Three kinds of spectral indicators, the water
vapor bands, methane band, and KI lines in J band, suggest that SDSS 1624+00 is
warmer and dustier than Gl 229B.Comment: 6 figures, to appear in PAS
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