123 research outputs found
Observation of elastic anomalies driven by coexisting dynamical spin Jahn-Teller effect and dynamical molecular spin state in paramagnetic phase of the frustrated MgCrO$
Ultrasound velocity measurements of magnesium chromite spinel MgCrO
reveal elastic anomalies in the paramagnetic phase that are characterized as
due to geometrical frustration. The temperature dependence of the tetragonal
shear modulus exhibits huge Curie-type softening, which
should be the precursor to spin Jahn-Teller distortion in the antiferromagnetic
phase. The trigonal shear modulus exhibits nonmonotonic temperature
dependence with a characteristic minimum at 50 K, indicating a coupling
of the lattice to dynamical molecular spin state. These results strongly
suggest the coexistence of dynamical spin Jahn-Teller effect and dynamical
molecular spin state in the paramagnetic phase, which is compatible with the
coexistence of magnetostructural order and dynamical molecular spin state in
the antiferromagnetic phase.Comment: 6 pages, 3 figure
Elastic Instabilities within Antiferromagnetically Ordered Phase in the Orbitally-Frustrated Spinel GeCoO
Ultrasound velocity measurements of the orbitally-frustrated GeCoO
reveal unusual elastic instabilities due to the phonon-spin coupling within the
antiferromagnetic phase. Shear moduli exhibit anomalies arising from the
coupling to short-range ferromagnetic excitations. Diplike anomalies in the
magnetic-field dependence of elastic moduli reveal magnetic-field-induced
orbital order-order transitions. These results strongly suggest the presence of
geometrical orbital frustration which causes novel orbital phenomena within the
antiferromagnetic phase.Comment: 5 pages, 3 figure
Coulomb correlations intertwined with spin and orbital excitations in LaCoO
We carried out temperature-dependent (20 - 550 K) measurements of resonant
inelastic X-ray scattering on LaCoO to investigate the evolution of its
electronic structure across the spin-state crossover. In combination with
charge-transfer multiplet calculations, we accurately quantized the
renormalized crystal-field excitation energies and spin-state populations. We
show that the screening of the on-site Coulomb interaction of 3d electrons is
orbital selective and coupled to the spin-state crossover in LaCoO. The
results establish that the gradual spin-state crossover is associated with a
relative change of Coulomb energy versus bandwidth, leading to a Mott-type
insulator-to-metal transition.Comment: 6 pages, 4 figures. Submitted to Phys. Rev. Let
Emergence of magnetic long-range order in frustrated pyrochlore NdIrO with metal-insulator transition
In this study, we performed powder neutron diffraction and inelastic
scattering measurements of frustrated pyrochlore NdIrO, which
exhibits a metal-insulator transition at a temperature of 33 K.
The diffraction measurements revealed that the pyrochlore has an
antiferromagnetic long-range structure with propagation vector of
(0,0,0) and that it grows with decreasing temperature below 15 K. This
structure was analyzed to be of the all-in all-out type, consisting of highly
anisotropic Nd magnetic moments of magnitude ,
where is the Bohr magneton. The inelastic scattering measurements
revealed that the Kramers ground doublet of Nd splits below . This suggests the appearance of a static internal magnetic field at the
Nd sites, which probably originates from a magnetic order consisting of
Ir magnetic moments. Here, we discuss a magnetic structure model for the
Ir order and the relation of the order to the metal-insulator transition in
terms of frustration.Comment: 6 pages, 1 table, 3 figure
Magnetic Frustration Driven by Itinerancy in Spinel CoV2O4
Localized spins and itinerant electrons rarely coexist in geometrically-frustrated spinel lattices. They exhibit a complex interplay between localized spins and itinerant electrons. In this paper, we study the origin of the unusual spin structure of the spinel CoV2O4, which stands at the crossover from insulating to itinerant behavior using the first principle calculation and neutron diffraction measurement. In contrast to the expected paramagnetism, localized spins supported by enhanced exchange couplings are frustrated by the effects of delocalized electrons. This frustration produces a non-collinear spin state even without orbital orderings and may be responsible for macroscopic spin-glass behavior. Competing phases can be uncovered by external perturbations such as pressure or magnetic field, which enhances the frustration
Development of Plasma Vitellogenin Assay for Estrogenic Effects of Endocrine-Disrupting Chemicals Using Ovariectomized Goldfish (Carassius auratus)
Plasma vitellogenin (VTG) assay was developed using ovariectomized goldfish (Carassius auratus) for determining the estrogenic effects of endocrine-disrupting chemicals. In a laboratory study, we assessed the estrogenic activity of commercial fish diets by using a diet for ornamental carp (CD) and a casein-based formulated fish diet (FD), which was shown to not contain soybean or fish meal in a previous study. In ovariectomized fish, plasma VTG concentrations were significantly higher in the CD-fed group than in the FD-fed group. These results indicate that the estrogen activity of CD may be high enough to cause induction of plasma VTG in ovariectomized goldfish as previously observed in male goldfish. Moreover, the effect of estrogen on plasma VTG induction was confirmed by significant plasma VTG production following the exposure of FD-fed ovariectomized goldfish to a nominal estradiol-17ÎČ concentration of 100 ÎŒg/l for 31 days. Our data suggest that induction of plasma VTG using ovariectomized goldfish is a good tool for evaluating the estrogenic effects of endocrine-disrupting chemicals
An Efficient Approach to the Synthesis of Novel Pyrene-Fused Azaacenes
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Organic Letters (copyright © American Chemical Society) after peer review and technical editing by the publisher.
To access the final edited and published work see: http://dx.doi.org/10.1021/ol401438
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