Crystal and magnetic structures of the mineral centennialite ${\mathrm{CaCu}}_{3}{(\mathrm{OH})}_{6}{\mathrm{Cl}}_{2}\ifmmode\cdot\else\textperiodcentered\fi{}0.6{\mathrm{H}}_{2}\mathrm{O}$ are investigated by means of synchrotron x-ray diffraction and neutron diffraction measurements complemented by density functional theory (DFT) and pseudofermion functional renormalization group (PFFRG) calculations. ${\mathrm{CaCu}}_{3}{(\mathrm{OH})}_{6}{\mathrm{Cl}}_{2}\ifmmode\cdot\else\textperiodcentered\fi{}0.6{\mathrm{H}}_{2}\mathrm{O}$ crystallizes in the $P\overline{3}m1$ space group and ${\mathrm{Cu}}^{2+}$ ions form a geometrically perfect kagome network with antiferromagnetic ${J}_{1}$. No intersite disorder between ${\mathrm{Cu}}^{2+}$ and ${\mathrm{Ca}}^{2+}$ ions is detected. ${\mathrm{CaCu}}_{3}{(\mathrm{OH})}_{6}{\mathrm{Cl}}_{2}\ifmmode\cdot\else\textperiodcentered\fi{}0.6{\mathrm{H}}_{2}\mathrm{O}$ enters a magnetic long-range ordered state below ${T}_{\text{N}}=7.2$ K, and the $\mathbf{q}=\mathbf{0}$ magnetic structure with negative vector spin chirality is obtained. The ordered moment at 0.3 K is suppressed to $0.58(2){\ensuremath{\mu}}_{\text{B}}$. Our DFT calculations indicate the presence of antiferromagnetic ${J}_{2}$ and ferromagnetic ${J}_{d}$ superexchange couplings of a strength which places the system at the crossroads of three magnetic orders (at the classical level) and a spin-$\frac{1}{2}$ PFFRG analysis shows a dominance of $\mathbf{q}=\mathbf{0}$ type magnetic correlations, consistent with and indicating proximity to the observed $\mathbf{q}=\mathbf{0}$ spin structure. The results suggest that this material is located close to a quantum critical point and is a good realization of a ${J}_{1}\ensuremath{-}{J}_{2}\ensuremath{-}{J}_{d}$ kagome antiferromagnet.
We report two cases of enhanced S-cone syndrome (ESCS), one in a patient observed for 20 years since age 31 and the other in an elderly patient with ESCS who underwent cataract surgery.Case 1. A 31-year-old man complained of night blindness and decreased vision. At the initial visit, his corrected visual acuity was 0.7 OD and 0.3 OS. Funduscopy revealed retinal degeneration near the vascular arcade and cystic change in the macular area in both eyes. It was diagnosed as ESCS by electroretinogram (ERG) findings. During a 20-year observation, the cystic change in the macular area became ambiguous and pigmentation appeared in the retinal degeneration region, Goldmann perimetry showed remarkable constriction of I /4 isopter, and ERG showed reduction of amplitude. At age 50, his corrected visual acuity was 0.4 OD and 0.4 OS. Case 2. A 78-year-old woman complained of night blindness and decreased vision. At the initial visit, her corrected visual acuity was 0.03 OD and 0.07 OS. Advanced nuclear cataract was seen in both eyes, and funduscopy revealed retinal degeneration near the vascular arcade. It was diagnosed as ESCS by ERG findings. Cataract surgery was done in both eyes, and postoperative visual acuity was 0.3 OD and 0.2 OS, and she has maintained the same visual acuity for two years.These cases indicate that retinal function of patients with ESCS decreases gradually after middle age, and that even if a cystic change in the macular area becomes ambiguous, vision does not improve. Some retinal function of ESCS patients can be maintained into old age.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
The magnetic structure and magnetoelectric effect have been investigated for single crystals of the antiferromagnet ${\mathrm{Co}}_{4}{\mathrm{Nb}}_{2}{\mathrm{O}}_{9}$. Single-crystal neutron diffraction and magnetic susceptibility measurement have revealed that the magnetic structure is different from a collinear arrangement with spin parallel to the trigonal axis as proposed previously. ${\mathrm{Co}}^{2+}$ magnetic moments are found to be almost lying in the basal plane, which lowers the magnetic symmetry to $C2/{c}^{\ensuremath{'}}$ with the propagation vector $\mathbit{k}=0$. Associated with the magnetic phase transition, a sharp anomaly in the dielectric constant and displacement current indicate the appearance of the magnetoelectric below N\'eel temperature ${T}_{N}$ with a large coupling constant up to 30 ps/m. The existence of off-diagonal components in a magnetoelectric tensor indicate the formation of ferrotoroidic order in ${\mathrm{Co}}_{4}{\mathrm{Nb}}_{2}{\mathrm{O}}_{9}$. Such a magnetoelectric effect can be ascribed to the reduction of symmetry caused by simple antiferromagnetic order in a honeycomb network.
We have grown large single crystals of SrNbO${}_{3.4+d}$ ($d\ensuremath{\sim}0.03$) with $n=5$ in the homologous series Sr${}_{n}$Nb${}_{n}$O${}_{3n+2}$ by using a traveling solvent floating-zone method and measured resistivity, thermopower, and thermal conductivity along all crystallographic axes. The thermoelectric properties are found to be highly anisotropic, which reflects a quasi-one-dimensional electronic structure. In particular, the thermopower along the $b$ axis is $\ensuremath{-}170$ $\ensuremath{\mu}$V/K at 300 K, which is 1 order of magnitude higher than the $\ensuremath{-}15$ $\ensuremath{\mu}$V/K along the $a$ axis and $\ensuremath{-}25$ $\ensuremath{\mu}$V/K along the $c$ axis. A possible origin of the high anisotropy in the thermopower is discussed in terms of dimensional crossover associated with a structural modification.
