Magnons and electromagnons in a spin-lattice-coupled frustrated magnet CuFeO2 as seen via inelastic neutron scattering

We have investigated spin-wave excitations in a four-sublattice (4SL) magnetic ground state of a frustrated magnet CuFeO2, in which `electromagnon' (electric-field-active magnon) excitation has been discovered by recent terahertz time-domain spectroscopy [Seki et al. Phys. Rev. Lett. 105 097207 (2010)]. In previous study, we have identified two spin-wave branches in the 4SL phase by means of inelastic neutron scattering measurements under applied uniaxial pressure. [T. Nakajima et al. J. Phys. Soc. Jpn. 80 014714 (2011) ] In the present study, we have performed high-energy-resolution inelastic neutron scattering measurements in the 4SL phase, resolving fine structures of the lower-energy spin-wave branch near the zone center. Taking account of the spin-driven lattice distortions in the 4SL phase, we have developed a model Hamiltonian to describe the spin-wave excitations. The determined Hamiltonian parameters have successfully reproduced the spin-wave dispersion relations and intensity maps obtained in the inelastic neutron scattering measurements. The results of the spin-wave analysis have also revealed physical pictures of the magnon and electromagnon modes in the 4SL phase, suggesting that collinear and noncollinear characters of the two spin-wave modes are the keys to understand the dynamical coupling between the spins and electric dipole moments in this system.Comment: 8 pages, 6 figure

Chemical properties of surface waters in the limestone regions of western Japan: Evaluation of chemical conditions for the deposition of tufas

In order to understand the chemical conditions for the depositionof tufas, chemical properties of were investigated for the 201 surface waters collected from the limestone regions including newly discovered localities of tufas. The collected waters were categorized, according to the association with tufas, mainly into; category N (waters without tufa deposition), category T (waters depositing tufas), and category S (spring waters of tufa-depositing streams). These three categories clearly differ in Ca contents, equilibrium CO 2 partial pressure (PCO2), and saturation index for calcite (SIC); all of which are the most important chemical properties for the deposition of tufas. The waters of the category N are characterized by small Ca contents (mainly 15～35 ppm) and low PCO2(350～1,000 µatm) which indicate that they are basically flowing on a limestone substrate without an efficient CO2 uptake from soils. Their SIC never exceeds +0.5. The waters depositing tufas (category T) normally exhibitCa contents more than 45 ppm and PCO2 ranging 500～2,000 µatm. The waters of category S show comparable or slightly larger Ca contents than category T, however their PCO2 is considerably higher (than 2,000 µatm). Their raised values of Ca contents and PCO2 are ascribed to efficient CO2 uptake in a soil layer and subsequent dissolution of CaCO3. Furthermore, their SIC around 0.0 indicates that the waters dissolve CaCO3 until they reach the saturation in underground water systems. The large difference in PCO2 between categories T and S results from degassing of CO2 during flowing on the streams. The degassing increases pH and SIC of the waters. The SIC of category T mostly exceeds +0.5, that is probably the most important chemical condition for an efficient deposition of tufas. This study indicates that tufas are not very rare, but also that their distribution tends to be concentrated in a certain area, such as northwestern Okayama Prefecture. Local geological and hydrological conditions can be also important controls for deposition of tufas

Magnetic Phase Diagrams with Possible Field-induced Antiferroquadrupolar Order in TbB2_2C2_2

Magnetic phase diagrams of a tetragonal antiferromagnet TbB$_2$C$_2$ were clarified by temperature and field dependence of magnetization. It is noticeable that the N{\'e}el temperature in TbB$_2$C$_2$ is anomalously enhanced with magnetic fields, in particular the enhancement reaches 13.5 K for the ${}$ direction at 10 T. The magnetization processes as well as the phase diagrams are well interpreted assuming that there appear field-induced antiferroquadrupolar ordered phases in TbB$_2$C$_2$. The phase diagrams of the AFQ compounds in RB$_2$C$_2$ are systematically understood in terms of the competition with AFQ and AFM interactions.Comment: 4 pages, 4 figures, RevTeX

Regulation of dynamic structure of cyclophanes by their complexation with the porphyrin

Dithia[3.3]metacyclophanes which consist of the pyridine unit connecting to the different positions of the parent cyclophane skeleton have been prepared. Conformational change has been observed for the cyclophane having a 4-substituted pyridine unit by binding to the porphyrin. In contrast the porphyrin binding has no influence on conformational behavior of the cyclophane having a 3-substituted pyridine unit

Replica symmetry breaking in an adiabatic spin-glass model of adaptive evolution

We study evolutionary canalization using a spin-glass model with replica theory, where spins and their interactions are dynamic variables whose configurations correspond to phenotypes and genotypes, respectively. The spins are updated under temperature T_S, and the genotypes evolve under temperature T_J, according to the evolutionary fitness. It is found that adaptation occurs at T_S < T_S^{RS}, and a replica symmetric phase emerges at T_S^{RSB} < T_S < T_S^{RS}. The replica symmetric phase implies canalization, and replica symmetry breaking at lower temperatures indicates loss of robustness.Comment: 5pages, 2 figure

Regulation of dynamic structure of cyclophanes by their complexation with the porphyrin

Dithia[3.3]metacyclophanes which consist of the pyridine unit connecting to the different positions of the parent cyclophane skeleton have been prepared. Conformational change has been observed for the cyclophane having a 4-substituted pyridine unit by binding to the porphyrin. In contrast the porphyrin binding has no influence on conformational behavior of the cyclophane having a 3-substituted pyridine unit