黒江 晴彦

Preparation conditions of titanium oxide (TiO₂) powders were examined by the hydrolysis of titanium potassium oxalate (K₂TiO(C₂O₄)₂), through the homogeneous precipitation method (80oC for 24 h) and hydrothermal treatment (160 or 170oC for 1 h). According to the Rietveld analysis, almost a single phase of anatase TiO₂ could be obtained by the hydrothermal treatment at 160oC for 1 h, followed by the heating at 900oC for 10 min in air. The molar ratio of anatase to rutile TiO₂ was found to be controlled by optimizing the hydrothermal conditions in the solution and the heating conditions in air for the photocatalytic activity.

Low-Temperature magnetic properties were investigated on the gold nano particles (GNPs) with an average size of 11.5 nm, assembled with molecules of ruthenium complex (Ru0), and phenylboronic acid (B0) by the proton nuclear magnetic resonance (1H-NMR) and susceptibility measurements. The temperature dependence of the NMR shift and the uniform susceptibility was described as the sum of the Curie-Weiss term and a positive constant term. From the former, the average number of Ru0 on each GNP was estimated to be 118, which is 23% of the calculation. The finite positive constant term shows a clear contrast with the well-known fact that the bulk gold is diamagnetic. Finally, a disappearance of the motional narrowing effect in the proton NMR spectra below 60 K indicates that the wavering motion of Ru0 complexes on GNP at room temperature is frozen at low temperatures.

© 2018 American Physical Society. The previously reported ordered moment vector is one-fourth of the correct one. This Erratum was caused by the mistake in the scale factor. The correct ordered moment vector is [ 0.10 ( 5 ) , 2.41 ( 4 ) , - 1.42 ( 6 ) ] μ B . Its magnitude is 2.92 ( 7 ) μ B . The ellipse in the previous Fig. 7 indicates the second-shortest Cr-Cr pair (not the shortest pair). In the present Fig. 7, the shortest, second-shortest, and third-shortest Cr-Cr pairs are indicated by solid red, dotted green, and dashed blue lines, respectively. The exchange interaction is ferromagnetic in the shortest Cr-Cr pair ( 3.01 ). Probably, the dominant antiferromagnetic interaction exists in the second-shortest pair ( 4.97 ) or in the third-shortest pair ( 5.24 ). (Figure Presented). The authors thank V. Y. Pomjakushin for pointing out our errors.

We measured magnetization, specific heat, electron spin resonance, neutron diffraction, and inelastic neutron scattering of CrVMoO7 powder. An antiferromagnetically ordered state appears below T-N = 26.5 +/- 0.8 K. We consider that the probable spin model for CrVMoO7 is an interacting antiferromagnetic spin-3/2 dimer model. We evaluated the intradimer interaction J to be 25 +/- 1 K and the effective interdimer interaction J(eff) to be 8.8 +/- 1 K. CrVMoO7 is a rare spin dimer compound that shows an antiferromagnetically ordered state at atmospheric pressure and zero magnetic field. The magnitude of ordered moments is 0.73(2) mu(B). It is much smaller than a classical value similar to 3 mu(B). Longitudinal-mode magnetic excitations may be observable in single crystalline CrVMoO7.

The effects of electric fields perpendicular to the c-axis of the trigonal cell in single crystals of BiFeO3 are investigated through magnetization and resistance measurements. Magnetization and resistance exhibit hysteretic changes under applied electric fields, which can be ascribed to the reorientation of the magnetoelectric domains. Samples are repetitively switched between high-and low-resistance states by changing the polarity of the applied electric fields over 20 000 cycles at room temperature. These results demonstrate the potential of BiFeO3 for use in non-volatile memory devices. Published by AIP Publishing.

© 2015 American Physical Society. ©2015 American Physical Society. We investigated the crystal and magnetic structures of the spin-12 frustrated antiferromagnet Cu3Mo2O9 in which the spin system consists of antiferromagnetic chains and dimers. The space group at room temperature has been reported to be orthorhombic Pnma (No. 62). We infer that the space group above TN=7.9K is monoclinic P21/m (No. 11) from the observation of reflections forbidden in Pnma in x-ray powder diffraction experiments at room temperature. We determined the magnetic structure of Cu3Mo2O9 in neutron powder diffraction experiments. Magnetic moments on dimer sites lie in the ac planes. The magnitudes are (0.50∼0.74)μB. Moments on chain sites may exist but the magnitudes are very small. The magnetic structure indicates that a partially disordered state is realized. We consider the origin of the magnetic structure, weak ferromagnetism, and electric polarization.

© 2015 The Authors. Published by Elsevier B.V. We report the substitution effects of W6+ ions on multiferroic material Cu3Mo2O9 having a dis- torted tetrahedral quasi-one-dimensional spin structure. In Cu3Mo2O9, the weak ferromagnetic component of the spin moments and the ferroelectricity coexist below TN = 7.9K. In case of Cu3(Mo,W)2O9, the nonmagnetic Mo6+ ions are replaced with the nonmagnetic W6+ ions. We study the specific heat, magnetization, and dielectric constants, and show the magnetic-field- temperature phase diagrams in the single crystals with various W concentrations. We compare the phase diagram of Cu3(Mo,W)2O9 to that of (Cu,Zn)3Mo2O9 and discuss the similarity and the difference between the direct and the indirect substitution effects. The efficiency of the W substitution is much weaker than that of the Zn substitution.

© 2015 The Authors. Published by Elsevier B.V. It has been demonstrated that the muon spin rotation measurements under electric field give helpful information about the electrically induced magnetism, e.g., the cross correlation effects in multiferroic materials. We have developed an electric-field application system up to 500V for the Dolly spectrometer at the Paul Scherrer Institute. We report the electric-field effects on the μSR spectrum in the multiferroic material Cu3Mo2O9, where a slightly canted antiferromagnetic long-range order appears together with the ferroelectricity below 8K. In the muon-spin rotation spectrum at 1.5K, two kinds of the internal magnetic fields are clearly observed as a beating oscillation. The muon-spin spectrum depends on the electric fields along the c axis of the crystal along which the spontaneous electric polarization appears. From the fitting of the spectra in time and frequency domains, it is shown that the observation of the electric-field dependence on the muon-spin spectra clearly indicates a change of the internal magnetic fields induced by the application of the external electric fields. We propose a model with one muon-stopping site which explains the observed spectra qualitatively. This model is based on the magnetic excitations in Cu3Mo2O9 obtained from the inelastic neutron-scattering experiments.

© 2015 The Authors. Published by Elsevier B.V. Quasi one dimensional antiferromagnet Cu3Mo2O9 consists of spin chains and inequivalent spin pairs clinging on them, and shows the magnetic order at TN = 7.9K. The local structure of tetrahedron formed by neighboring four spins suggests a non-collinear spin structure in the ordered state and hence the multiferroicity. We have performed Cu-NMR measurements at low temperatures below TN and showed that the observed spectra are consistent with the report by the recent neutron elastic scattering experiments in that the chain site Cu has only an extremely small ordered moment.

We have investigated effects of impurity substitution of Fe for Co sites on magnetic and dielectric properties in CaBa(Co1-xFex)(4)O-7 crystals in magnetic fields. The non-doped compound, CaBaCo4O7 with the polar space group Pbn21, shows a large change of electric polarization AP along the c axis below a ferrimagnetic transition temperature. With increasing x, the transition temperatures for the ferrimagnetic and ferroelectric-like phases are shifted towards lower and these phases are completely collapsed above x=1.56%. We have also investigated the magnetic field effects for CaBa(Co1-xFex)407 crystal with a doping level x=0.5 where the ferrimagnetic and ferroelectric-like phases sustain. Then a relatively large magnetocapacitance, Delta epsilon(H)/epsilon(0) [epsilon(H) - epsilon(0)]/epsilon(0), of 45% at 58 K was observed, which is not significantly reduced from the parent compound.

133Cs/7Li-NMR study was performed on a quasi-two-dimensional spin system Cs2Mn3LiF12, in which S 2 Mn atoms form undistorted Kagome lattice. We have observed a clear splitting in the Li-NMR resonance line for a single crystal at low temperatures below TN 3.6 K. The longitudinal nuclear spin relaxation rate T-1 1 of both Cs and Li-NMR showed a critical divergence at the same temperature. These observations are considered to be a microscopic evidence for an occurrence of long range magnetic order due to a weak inter-plane spin interactions.

The conditions for the formation of hydroxyapatite [Ca-10(PO4)(6)(OH)(2); HAp] layer on the graphite sheet were examined via the processes of (i) the acid treatment of conc. nitric and sulfuric acids at 50 degrees C for 24 h for the formation of carboxyl group, and (ii) the external heating (90 degrees C, 1 h) and/or microwave heating (100 degrees C, 5 min) of the acid-treated graphite sheet in the "apatite-dissolved solution" prepared by bubbling CO2 gas into the HAp-dispersed water. The combination of external and microwave heating was effective in the formation of large amount of calcium phosphates, because the seed crystals of apatite formed by the evaporation of solvent from the apatite-dissolved solution (i.e., external heating) contributed to enhancing the formation of calcium phosphate layer through the microwave heating. The calcium phosphate layer formed by stacking the plate-like particles possessed the typical thickness of 4.9 mu m, and was identified as HAp with Ca/P ratio of 1.72 or carbonate-containing HAp. Based upon the graphite sheet with HAp layer implanted into femur and tibia of the Japanese white rabbit for 4 months, the formation of calcified bone at the interfaces was found to show the excellent biocompatibility. (C) 2013 The Ceramic Society of Japan. All rights reserved.

We have systematically investigated the magnetic and the dielectric properties of Eu-0.595(Y1-x Ho (x) )(0.405)MnO3 (0 a parts per thousand currency sign x a parts per thousand currency sign 1) single crystals with fine tunning of 4f magnetic moments while keeping the average size of the rare-earth (R) site the same. In the x = 0.3 crystal, the ferroelectric polarization along the c axis (P (c) ) emerges at 25 K; then, P (c) is suppressed, and P (a) appears simultaneously with decreasing temperature. On further decreasing temperature, P (a) disappears and P (c) appears again. The observed reentrant behavior of the P (c) phase indicates that the P (a) and the P (c) phases are strongly competing with each other.

We study the effects of Zn substitution on single crystals of the low-dimensional multiferroic material Cu3Mo2O9. We report the magnetic field-temperature phase diagram obtained from the temperature and the magnetic field dependences of the specific heat, the dielectric constant, the differential magnetization, and the electric polarization-electric field curve in Cu2.85Zn0.15Mo2O9. We obtain three phases: a paraelectric and a ferroelectric phase, and a ferroelectric phase with a large coercive electric field. The origin of the last one is discussed based on the charge redistribution effect on a half-filled Mott insulator. In this phase, the Zn substitution induces a robust localized ferroelectric polarization that increases the coercive electric field.

We study micro-Raman spectroscopy in free-standing single GaN nanocolumns with 0.45-2.1 μm diameters, which are synthesized by rf-plasma-assisted molecular beam epitaxy. We clearly observe the breakdown of the polarization selection rule of Raman spectra from E₂^H phonon, when the diameter of nanocolumn is thinner than four times the wavelength of incident light inside the sample. The selection rule gets recovered with increasing diameter of nanocolumn. Moreover, we observe quasi-TO phonon modes, which strongly affects the Raman spectra from the A₁(TO) and E₁(TO) phonons. [DOI: 10.1380/ejssnt.2012.321]

Magnetic excitation in strongly coupled spin monomer and dimer system is studied theoretically focusing on Cu3Mo2O9 as an typical example, where Cu3Mo2O9 shows an antiferromagnetic long-range order at zero field. Introducing formfactors of dimers, we present the formulation for magnetic excitations. Under an external magnetic field, an additional field-induced quantum phase transition takes place due to the stabilization of a triplet state of the dimer. The recent experimental study revealed that Cu3Mo2O9 shows an multiferroic behavior with an electric polarization in the magnetically ordered state. According to the field-induced transition, we find that the electric polarization should change drastically.

We measure Raman scattering in an interacting spin-dimer system KCuCl3 under hydrostatic pressures up to 5 GPa mediated by He gas. In the pressure-induced quantum phase, we observe a one-magnon Raman peak, which originates from the longitudinal magnetic excitation and is observable through the second-order exchange interaction Raman process. We report the pressure dependence of the frequency, halfwidth and Raman intensity of this mode.

A quasi-one-dimensional quantum spin antiferromagnet Cu 3 Mo 2 O 9 , which possesses the two spin degrees of freedom, the linear chain site and dimer-like site weakly interacting with one another, has recently been reported by permittivity and ESR to show a charge instability in its magnetically ordered state. In this article, we report the study on NMR and magnetization to show the existence of the field-induced magnetic phase transition accompanied by the charge anomaly at 8 T.

A new technique that employs a temperature gradient and a mechanical drive system in an image furnace, has been developed for the solid-state crystallization. A crystal is continuously grown from a polycrystalline feed rod by scanning the heating area along the length direction using a conventional floating zone furnace. This technique differs from the floating zone method since the grain growth is realized without a melt zone. Using this technique, we have succeeded in growing large single crystals of Cu3-xZrxMo2O9, with their size reaching circle star 6 mm x 65 mm. (C) 2011 Elsevier B.V. All rights reserved.

We clarify that the antiferromagnetic order in the distorted tetrahedral quasi-one-dimensional spin system induces electric polarization. In this system, the effects of low dimensionality and magnetic frustration are expected to appear simultaneously. We obtain the magnetic-field-temperature phase diagram of Cu3Mo2O9 by studying the dielectric constant and spontaneous electric polarization. Around the tricritical point at 10 T and 8K, the change in the direction of electric polarization causes a colossal magnetocapacitance. We calculate the charge redistribution in a small spin cluster consisting of two magnetic tetrahedra to demonstrate the electric polarization induced by the antiferromagnetism.

We study Raman scattering of GaN nanowalls and regularly-arrayed GaN nanocolumns, and observe a peak from surface phonon (SP) around 705 cm(-1). The Raman intensity of SP decreases with increasing wall width in GaN nanowalls, while it increases with increasing column diameter in GaN nanocolumns. The Raman peak of SP has different polarization characteristics between GaN nanowalls and nanocolumns.

Magnetic excitation in coupled multispin system is studied theoretically focusing on Cu 2 Fe 2 Ge 4 O 13 and Cu 2 CdB 2 O 6 as typical examples of such system. These compounds consist of spin dimer and spin monomer parts and show an antiferromagnetic phase transition at low temperatures due to the spin monomer part. A multispin containing a spin dimer and spin monomers is treated as a basis unit. The multispin forms a spin multiplet and its energy levels are separated into high and low regions reflecting the characteristic energies of the dimer and monomer parts. We regard the system as interacting multispins and apply an extended Holstein–Primakoff theory by introducing bosons for each energy level of a spin multiplet. In the low-energy region, the obtained magnon dispersion and dynamical spin correlation function agree quantitatively with experimental results of inelastic neutron scattering performed in Cu 2 Fe 2 Ge 4 O 13 . Analyzing dynamical spin correlation functions, we find several high-energy modes with longitudinal spin fluctuations peculiar to the coupled spin dimer and spin monomer system. One-magnon Raman scattering is studied to probe such longitudinal modes. Magnetic excitation in Cu 2 CdB 2 O 6 is also studied in the same way.

By means of Raman-scattering measurement under pressures at low temperatures we study the "devil's staircase"-type phase of NaV2O5. The spin-gap mode shows a drastic softening with increasing pressure up to 0.9 GPa in C-1/4 phase and disappears between 0.9 and 1 GPa. It appears again between 1 and 2.3 GPa in C-0 phase, indicating that this phase is also a spin-gap state. Taking the charge ordering into consideration, we discuss the spin-gap states and clarify that the spin-gap mode is created by the exchange-interaction Raman-scattering mechanism and it comes from a gap between the spin-singlet ground state and the S-x=0 spin-triplet excited one. This model explains that the spin gap is almost independent of the applied magnetic field and it vanishes at about 10 degrees lower than the critical temperature in C-1/4 phase.

A quasi-one-dimensional spin system Cu3Mo2O9, which has two spin degrees of freedom, the antiferromagnetic linear chain site and dimer-like site weakly interacting with each other, shows a 3D-antiferromagnetic order at T-N=7.9 K. We report the result of Cu-NMR on the single crystal of this system both in antiferromagnetic and paramagnetic states. In field-swept spectra, we observe two types of signals, which come from the chain site and the dimer-like site, respectively. With increasing resonant frequency, the signal from chain site shifts to lower magnetic field, while that from dimer-like site to higher field. This anomalous behaviour of the chain-site signal is explained in terms of the cancellation between the hyperfine field of about 8.5 T at the chain-site Cu and the applied field. A weak but finite hyperfine field of the dimer-like site indicates that there exists a localized spin on the site, indicating that it is not a singlet state.