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Since the success of synthesis the molecular structure of the endohedral metallofullerene is a most interesting subject in relation to the electronic state of metal and carbon cage. Highquality crystals of endohedral metallofullerene La@C82 have been synthesized by the arc discharge and HPLC method. The x-ray powder diffraction and the precession photograph of a tiny single crystal have revealed the cubic structure with the space group I43d and the lattice constant ao = 25.72 ± 0.007 Å at room temperature. The structure is characterized by the molecular arrangement in which the molecules align in the [111] direction with the molecular axis orienting in the same [111] direction; this structure suggests the existence of a dipole interaction between the molecules. The metal position in the cage is also discussed on the basis of an ellipsoidal model of molecule.

The 29 Si-NMR measurements on potassium-loaded zeolite LTA (K x /K 12 -Al 12 Si 12 O 48 ), where x is loaded potassium atoms per α -cage, were carried out. It was found that the NMR line-shape in the paramagnetic state is essentially the same for x =4–7, implying that the distribution and amplitude of the magnetic moment are quiet similar to each other. Possible distribution of the magnetic moment and the origin of the magnetic interactions are discussed.

The orbital ordering and spin state in the room-temperature ferromagnet Sr 3 YCo 4 O 10.5 were investigated by a resonant X-ray scattering technique. A resonating signal with a σ→π' scattering component was observed at ( h 00), where h =2 n +1 ( n : integer), near the 1 s → e g transition energy of Co. This provides direct evidence of not only e g orbital ordering but also the existence of the intermediate-spin (IS) state. Moreover, we suggest that the ferrimagnetism is induced by the e g orbital ordering of the IS state of Co 3+ . The peculiar e g orbital, spin-state, and magnetic orderings are also discussed.

We investigate phonon modes of the rare-earth filled skutterudite compounds CeRu 4 Sb 12 , CeOs 4 Sb 12 , PrRu 4 Sb 12 , and PrOs 4 Sb 12 by using an inelastic neutron scattering technique. These materials exhibit similar low-lying motions of filled ions inside the Sb cages that softens with decreasing temperature. Potentials at the rare-earth sites are considerably anharmonic. Despite that this behavior appears in all the four materials, magnitude of the softening of PrOs 4 Sb 12 is largest among them. This fact implies that difference of carrier state gives rise to renormalization effect on the rare-earth-ion vibrations.

Superlattice reflections in the multipole ordered phase of PrRu 4 P 12 and Pr(Ru 0.97 Rh 0.03 ) 4 P 12 has been measured using a synchrotron x-ray scattering technique. The Thomson scattering intensity of (111) at 1.7 K does not show significant variation with magnetic field up to 7 T in contrast to the reported variation of electrical resistivity. This means that the lattice distortion in the ordered phase is robust and the staggered ordering remains after split of triplet ground state at half of Pr sites. The nonmetallic staggered ordering is not destroyed completely by applying magnetic field. Energy scan at (111) reflection of Pr(Ru 0.97 Rh 0.03 ) 4 P 12 show temperature dependence around resonant energy of Pr L 3 edge. This may allow us to observe anisotropy of electronic ordering of Pr sites and gives us a hint for direct observation of higher rank multipole order in PrRu 4 P 12 .

Mechanism of successive ferroelectric–paraelectric phase transitions exhibited by an organic ferroelectric, trichloroacetamide, is clarified through structural and calorimetric experiments. The transition mechanism, intramolecular disordering, reasonably explains the polarization reversal. This mechanism is only possible in molecular solids and is applicable to other compounds as a possible strategy to design new molecular ferroelectrics. Also revealed is the incommensurate nature of the intermediate phase, the origin of which is briefly discussed at phenomenological and molecular levels.

Crystal field states of Pr 4f electrons of PrOs4P12 and PrRu4Sb12 were investigated by inelastic neutron scattering. Different spectral widths between two excitations from the ground state singlet to the triplets and their temperature evolutions are well reproduced by the theory based on the exchange coupling between 4f and conduction electrons (Becker K W et al. 1977 Z. Physik B 28 9). Shift of level energies by around 1 meV below 60 K were also observed. The results support the p-f hybridization effect in Pr-filled skutterudites.

We have performed inelastic neutron scattering and magnetic susceptibility measurements on Pr(Ru1−xRhx)4P12 (0 ≤ x ≤ 0.15), in which the antiferro-multipole ordering of PrRu4P12 is gradually suppressed with increasing x. The saturation of magnetic susceptibility at low temperature suggests that all the 4f-electron ground states are singlet for x ≥ 0.03, in contrast to the triplet and singlet ground states in the ordered phase of PrRu4P12. Neutron experiments show the presence of two types of crystal field (CF) level schemes: a temperature-dependent one similar to one of those observed in PrRu4P12 as signatures of the ordering, and an additional temperature-independent one indicating the existence of Pr ions which do not contribute to the ordering. Rh-substitution seems to have two effects: a local effect causing temperature-independent CF levels of Pr ions, and a wide-range effect causing switch of ground state. The ordering in low Rh-content compounds arises from the inequivalent CF level schemes that allow conserving the antiferro-type ordering pattern of multipoles through thermal excitation, despite the common ground state in compounds with x ≥ 0.03.

We present a X-ray diffraction study of Pr(Ru1−xRhx)4P12 (x = 0, 0.05), which exhibit a metal-nonmetal transition at about 50–60 K. Superlattice reflections which are related to [Ru,Rh] and P atom displacements could be observed below the transition temperature. In PrRu4P12, these displacements are found to increase gradually as the temperature decreases, in agreement with previous studies. In Pr(Ru0.95Rh0.05)4P12, the [Ru0.95Rh0.05] and P atom displacements first increase with decreasing temperature below 50 K, but nearly cancel at lowest temperatures. We discuss this unexpected structural behavior by considering the Pr 4f electron states in the Pr(Ru1−xRhx)4P12 compounds.

We studied optical absorption of single-walled carbon nanotubes by varying the dielectric environment. For the two different components of the broad UV-absorption feature conventionally referred to as the $\ensuremath{\pi}$ plasmon, we find that the component at 5.0--5.3 eV exhibits remarkable spectral changes, which we attribute to a dipolar radial surface plasmon. However, the component at $\ensuremath{\sim}4.5\text{ }\text{eV}$ remains unchanged, raising a fundamental question as to its conventional attribution. We discuss its relation with the absorption feature at $\ensuremath{\sim}4.5\text{ }\text{eV}$ in graphite arising from an interband transition.

Resonant magnetic x-ray diffraction experiments on the Shastry–Sutherland lattice TbB 4 were carried out under pulsed magnetic fields up to 30 T at 8 K. TbB 4 exhibits a multi-step magnetization process above 16 T below about 20 K when magnetic fields are applied along the c -axis. We examined the intensity of the 010 magnetic reflection as a function of magnetic field and found that the magnetization plateau phases are accompanied by large XY components of magnetic moments. We propose novel magnetic structures which consist of XY spins and Ising spins for the plateau phases. We also propose that energy level crossing and its inherent degeneracy give rise to the successive metamagnetic transitions in TbB 4 .

The orbital ordered states of V 3d in RVO3 (R=Y, Tb) have been investigated by a resonant x-ray scattering (RXS) technique. The RXS signals at (0 1 1) were measured near the V K-edge energy in the G-type orbital ordered (G-OO) phase. We found two kinds of the RXS signals, which reflect the orbital state and the local crystal symmetry. The former signal disappears in the orbital disordered phase, while the latter still survives. Moreover, the signals have different azimuthal angle dependence. Using the dependence of the RXS signal reflecting the orbital state, we evaluated the orbital ordered structure in the G-OO phase. Consequently, we succeeded in determining the G-type orbital arrangement of V orbitals by the RXS technique.

The crystal structure of [(LaMnO3)m(SrMnO3)m]n artificial superlattices and the valence distribution of Mn ions have been studied using the X-ray scattering technique. The stacking structures were determined by the scattering intensities in the out-of-plane direction. The Mn valence distributions were evaluated by the energy dependence of the scattering intensity near the Mn K-edge, which was analyzed on the basis of the obtained crystal structures. The result indicates that the Mn valence becomes 3+ (4+) in the LaMnO3 (SrMnO3) layers, and the valence has an intermediate value between 3+ and 4+ only at the interface between LaMnO3 and SrMnO3 layers. We have also clarified that all the films are insulators independent of the periodicity m.

The spin transition behavior of iron(II) complexes [Fe(4-NH 2 trz) 3 ](C m H 2m+1 SO 3 ) 2 · 2H 2 O (4-NH 2 trz=4-amino-1,2,4-triazole, m=1~9) was investigated by the magnetic measurement. The transition temperature T c became higher with increasing the length of alkyl chain of counter-ion, m, and saturated at m=5. The even-odd effect was observed in the hysteresis width, that is, the hysteresis width was wider for even m, narrower for odd m.

The unresolved phase transition at 80 K in YbAl 3 C 3 has been studied by X-ray diffraction. It has been confirmed that the transition is a structural one with atomic displacement. Superlattice reflections that appear below 80 K show that the crystal structure changes from hexagonal to orthorhombic. From the reflection conditions, we conclude that the space group in the low temperature phase is P b c a , where all the atoms occupy the general 8c site. By fitting the observed intensities, we present two possible models of atomic displacement. The displacement results in the deformation of the triangular lattice of Yb spins, which is considered to be responsible for the formation of a spin-singlet ground state at low temperatures.

Nanocrystals of La 1- x Sr x MnO 3+δ (0< x ≤0.51) with a diameter of about 8 nm were synthesized in the pores of the mesoporous silica SBA-15. The crystal structure at all Sr concentrations had a rhombohedral symmetry. The temperature dependence of the magnetization showed ferromagnetic and superparamagnetic behavior, and the magnetization curves indicate the coexistence of a ferromagnetic and an antiferromagnetic component. ESR spectra were observed even at 77 K and were well reproduced by the summation of two absorption lines with either a Gaussian or a Lorentzian profile. The temperature dependence in the ESR spectra suggests the coexistence of two components with two transition temperatures. The magnetic phase of the nanocrystals indicates the coexistence of a ferromagnetic and an antiferromagnetic phase at all Sr concentrations studied (0< x ≤0.51), with a smooth Sr dependence of the two transition temperatures. The experimental results suggest the existence of a phase separation into a ferromagnetic...

The detailed crystal structure of a mixed-valent skutterudite SmOs 4 Sb 12 has been investigated by synchrotron radiation powder diffraction. Although the lattice parameter monotonically decreases with decreasing temperature, Sm–Sb bond length decreases rapidly below 150 K. The temperature dependence of the bond length coincides with that of the change in the valence of the Sm ion. These facts suggest that the hybridization between 4 f - and conduction electrons is enhanced at low temperatures. In addition, an isotropic thermal atomic displacement parameter of the Sm ion is much larger than those of the Os and Sb ions. This fact indicates the presence of an anharmonic vibration of Sm ions.

PrFe 4 P 12 exhibits clear heavy electron behaviors as well as the phase transition to an antiferro-type ordering of 4 f electron state. In this paper, we report on inelastic neutron scattering results for powdered samples of Pr x La 1- x Fe 4 P 12 ( x = 1.00 and 0.85). A clear quasielastic magnetic response is observed, and no distinct signal is seen for crystal-field (CF) excitations in the heavy electron state. A model with strong hybridization between conduction electrons and Pr 3+ 4 f 2 electrons [J. Otsuki et al. : J. Phys. Soc. Jpn. 74 (2005) 200 and 2082] is consistent with the observed magnetic response. This result shows that the heavy electron behavior of Pr x La 1- x Fe 4 P 12 ( x = 1.00 and 0.85) originates from the Kondo effect associated with low-lying singlet–triplet CF states.

The successive magnetic phase transitions of HoB 4 with T N1 =7.1 K and T N2 =5.7 K have been investigated in detail by neutron and X-ray diffraction. Since Ho ions in the c -plane form a Shastry–Sutherland lattice, geometrical frustration has been expected in this compound. Below T N1 , HoB 4 exhibits an incommensurate antiferromagnetic order with q =(δ, δ, δ') (δ=0.022, δ'=0.43), followed by a first-order transition at T N2 into a commensurate order with q =(0, 0, 0), where four magnetic moments are antiferromagnetically coupled in a unit cell. After determining the magnetic structures of the two phases by neutron powder diffraction, we pay particular attention to diffuse scatterings responsible for the critical behavior. Very broad diffuse scatterings, extending almost to the zone boundary, are observed already in the paramagnetic phase at around q =(0, 0, 0) and (0, 0, 1/2) with magnetic correlation lengths of ξ< 10 A. Below T N1 , a strong diffuse scattering develops in a more concentrated region at ...

Using neutron and resonant X-ray scattering, we studied crystal structure and charge-ordering pattern in La 1.5 Ca 0.5 CoO 4 . Taking A 2 m m with a – b type twin structure into account, Co 2+ /Co 3+ checkerboard charge ordering pattern was suggested in La 1.5 Ca 0.5 CoO 4 by neutron scattering structure analysis. In order to clarify the charge ordering pattern and the valences of the two Co sites, we performed a resonant X-ray scattering (RXS) measurement near the Co K -edge. We found a resonant signal at (3, 0, 0) reflection which corresponds to the charge ordering with a Co 2+ /Co 3+ checkerboard pattern, and the Co valences of charge ordering were fully charge disproportionated. From the X-ray fluorescence spectra, we found the pre-edge peak structures at E =7.710 and 7.713 keV, corresponding to 1 s → t 2 g and 1 s → e g transitions, respectively. The polarization dependence of the latter one suggests that the anisotropy e g orbital is realized in La 1.5 Ca 0.5 CoO 4 .

Orbital ordering state of 3 d electrons in YTiO 3 has been studied by magnetic Compton profile (MCP) measurement for crystallographic directions of [100] ( a -axis) and [001] ( c -axis). The magnetic effect of the observed MCP leads to the spin moment that is equal to the saturated magnetic moment within the estimated errors, which strongly suggests quenching of the orbital moment. Shape of the observed MCPs shows directional anisotropy between the two axes. The MCPs are calculated by using an atomic model wave function of a linear combination of two 3 d – t 2 g orbitals, u d y z ± v d z x ( u 2 + v 2 =1) for the Ti sites. The observed MCP is best reproduced by the calculated MCP with u =0.84±0.04 and v =0.54±0.04. This value of u is slightly larger than those obtained in the previous studies.

Structural study of orbital-ordered manganite thin films has been conducted using synchrotron radiation, and a ground state electronic phase diagram is made. The lattice parameters of four manganite thin films, Nd0.5Sr0.5MnO3 (NSMO) or Pr0.5Sr0.5MnO3 (PSMO) on (011) surfaces of SrTiO3 (STO) or [(LaAlO3){0.3}(SrAl0.5Ta0.5O3){0.7}] (LSAT), were measured as a function of temperature. The result shows, as expected based on previous knowledge of bulk materials, that the films' resistivity is closely related to their structures. Observed superlattice reflections indicate that NSMO thin films have an antiferro-orbital-ordered phase as their low-temperature phase while PSMO film on LSAT has a ferro-orbital-ordered phase, and that on STO has no orbital-ordered phase. A metallic ground state was observed only in films having a narrow region of A-site ion radius, while larger ions favor ferro-orbital-ordered structure and smaller ions stabilize antiferro-orbital-ordered structure. The key to the orbital-ordering transition in (011) film is found to be the in-plane displacement along [0-1 1] direction., Comment: 19pages, 11 figures

Etude cinetique de la nucleation et de la croissance pour une transition du premier ordre appartenant au systeme monodimensionnel a non-conservation des parametres d'ordre, dans un compose d'insertion rubidium-graphite. Caracterisation du volume de la phase en croissance et de l'evolution de la taille du noyau vis-a-vis du temps

Dynamics of rare-earth ions in filled skutterudite compounds PrT4Sb12 (T = Ru and Os) has been investigated by a neutron inelastic scattering technique. We found an optical mode located at extremely low energy around 4 meV exhibiting apparent softening behavior by 10 - 30% from 300 to 10 K. This softening mode is attributed to the motion of the filled Pr ions bound in anharmonic potential within the Sb cage. In addition, quasielastic responses near the Brillouin zone center indicate relaxation modes. These features can be explained in terms of a mode coupling scenario involving the motion of the filled Pr ions with huge amplitude.

The magnetic field-induced valence transition in YbInCu 4 has been studied by X-ray absorption spectroscopy at the Yb L III -edge up to 41 T. The field-induced valence transition is clearly observe...

The rare-earth tetraborides, RB4 with a tetragonal structure of space group P4=mbm (No. 127), have been attracting interest from the viewpoint of geometrical frustration. The lattice of rare-earth ion consists of squares and triangles, whose configuration within the c-plane is topologically equivalent to the two dimensional model studied by Shastry and Sutherland. Since the magnetic interaction in RB4, probably of Ruderman–Kittel–Kasuya–Yoshida (RKKY) type, is three dimensional and long-ranged, most compounds exhibit long-range magnetic orderings; therefore, the frustration effect may not be so apparent. However, various kinds of anomalous properties have been revealed recently, which we speculate to be relevant to the frustrated lattice. TbB4 exhibits two phase transitions at TN1 1⁄4 44K and TN2 1⁄4 24K. Magnetic susceptibilities for H k a ( a) and H k c ( c) both show a cusp at TN1, followed by a weak kink at TN2. 4) Although the cusp at TN1 for both field directions suggests existence of c-axis and c-plane components in the antiferromagnetic moments, the magnetic structure deduced from neutron diffraction is collinear type, where the moments are orientated along the a-axis and involves no c-axis component. However, the magnetic structures of GdB4, 7,8) DyB4, 9) and HoB4, 10) which have been clarified recently, are non-collinear and the latter two have c-axis component as well. Therefore, it is necessary to reinvestigate the magnetic structure of TbB4. The difference in the structure between the intermediate phase (TN1 T TN2) and the lowtemperature phase (TN2 T) has not yet been clarified. In addition, recent discovery of the multistep magnetization process in high fields for H k c also requires detailed knowledge on the magnetic structure of TbB4. 11) Powder sample of TbB4 was obtained by reacting terbium oxide and boron powders in vacuum using a high frequency furnace. The reaction was repeated twice to reduce the impurity phase of TbB6. B isotope was used to prevent absorption of neutrons by B. The magnetic susceptibility of the powder sample showed a cusp at TN1 1⁄4 44K and a kink at TN2 1⁄4 22K. Neutron powder diffraction experiment was performed on the Kinken powder diffractometer for high efficiency and high resolution measurements, HERMES, of Institute for Materials Research, Tohoku University, installed at the JRR-3 reactor in JAEA, Tokai. Neutrons with a wavelength of 1.8142 A were obtained by the 331 reflection of Ge monochromator and the collimation of 120-blank-sample-220 was employed. The powder sample of 5.053 g was filled in a vanadium cylinder with a diameter of 7mm and was sealed in a standard aluminium cell with helium gas. The cell was cooled with a closed cycle He-gas refrigerator. Figure 1 shows the powder pattern for the three phases of TbB4. The pattern at 50K shows the nuclear peaks, impurity peaks of TbB6, and relatively large background with a significant modulation around 2 13 . This modulation disappears in the pattern at 300K, indicating that this is due to magnetic diffuse scattering. As demonstrated in the inset, the intensity decreases abruptly below TN1. Note that the thermal diffuse scattering also contributes to the background at high temperatures, especially to the data at 300K. Although it is an interesting viewpoint whether the diffuse scattering is relevant to the frustration, there seems no significant difference in the intensity just above TN as compared with that of TbB2C2 without geometrical frustration. Structural parameters at 300K were refined by the Rietveld method with RIETAN-2000. The parameters obtained are as follows: a 1⁄4 7:120ð1Þ A, c 1⁄4 4:0294ð7Þ A, xTbð4gÞ 1⁄4 0:3172ð2Þ, zB1ð4eÞ 1⁄4 0:2007ð6Þ, xB2ð4hÞ 1⁄4 0:0869ð2Þ, xB3ð8jÞ 1⁄4 0:1773ð2Þ, yB3ð8jÞ 1⁄4 0:0395ð2Þ. Fraction of TbB6 impurity phase is 7.46%, and the reliability factors are Rwp 1⁄4 5:85, Re 1⁄4 3:34, and S 1⁄4 1:75. In order to determine the magnetic structure, we compared the calculated powder patterns for possible models with the experimental data. Since all the magnetic peaks in Figs. 1(a) and 1(b) can be indexed by integer numbers, we see that the unit cell of the magnetic structure is the same as that of the chemical one. Note that the magnetic peaks of TbB6 impurity phase, with TN 1⁄4 19:5K, is recognized in Fig. 1(a), which can be indexed by q 1⁄4 ð1=4; 1=4; 1=2Þ. There are twelve sets of basis structures that are classified by the irreducible representations; three of them are picked up in Fig. 2. Model B is realized in GdB4, model A in the intermediate phase of DyB4, and superposition of models A and C in the lowest temperature phase of DyB4 and HoB4. 7–10) We calculated the powder pattern for the twelve models by considering the nuclear and magnetic structure factors, Lorentz factor, scale factor, and absorption correction. We used the result of Rietveld analysis at 50K to calculate the nuclear structure factor. Gaussian peak profile was assumed, whose width was obtained from the fitting at 50K. Background was fitted with a polynomial function. Calculated pattern for 50K is shown by the solid line in Fig. 1(c). At 25K, model B in Fig. 2 best explains the data. As shown by the solid line in Fig. 1(b), the intensities of all the reflections can be reproduced by the calculation, which is not the case in other models. Therefore, in the region TN1 T TN2, the magnetic structure is expressed by the model B, where the moments lie in the c-plane and are noncollinear. The magnitude of the magnetic moment at 25K was deduced to be 7.2 B from the scale factors of nuclear and magnetic reflections. The powder pattern at 3K can be explained well only by increasing the magnetic scale factor on model B. However, there are a few reflections whose intensities cannot be reproduced. The most typical case is the 110 reflection. Although the magnetic structure factor vanishes in model B, the intensity clearly increases below TN2 as shown in Fig. 3(a). This increase can be explained by mixing the model A or C as demonstrated by the solid line. The B+A E-mail: tmatsu@iiyo.phys.tohoku.ac.jp Journal of the Physical Society of Japan Vol. 76, No. 1, January, 2007, 015001 #2007 The Physical Society of Japan

LaMnO 3+δ nanocrystals with a mean diameter of 75 A, were synthesized using SBA-15 mesoporous silica. The magnetic properties of the nanocrystals showed a novel size effect and were quite different from those of bulk crystal. The magnetic and electron spin resonance measurement results indicate that the existence of two transition temperatures, 278 and 235 K, which are higher than Neel and Curie temperature of bulk LaMnO 3+δ . The ESR spectrum was observed even at the lower transition temperature and consisted of the two broad lines whose shape changed at each transition temperature. The magnetization curve at 77 K was well reproduced by the summation of the two superparamagnetic magnetizations corresponding to antiferromagnetic and ferromagnetic nanoparticles, respectively. These results suggest that there are noninteracting ferromagnetic and antiferromagnetic nanoparticles with transition temperatures of 278 and 235 K, respectively.

Resonant X-ray scattering (RXS) in Y 1- x Ca x TiO 3 has been investigated near the Y K -edge. The resonant signal has been clearly found at a forbidden reflection, (500), and the intensity shows an azimuthal angle dependence with a twofold symmetry. The RXS intensities have almost no Ca concentration dependence, although the RXS intensities at the Ti K -edge markedly decrease with increasing Ca concentration. The origin of the RXS at the Y K -edge is clarified to be the deviation from 180° of the Ti–O–Ti bond angle, namely, the tilts of the octahedra around the Y ion. We also discuss the RXS mechanism at the main edge of the Ti K -edge.

We report on the structural and electronic properties of solid-solution films consisting of perovskite band insulators, SrTiO3 and LaAlO3, with a chemical formula of Sr1-xLaxTi1-xAlxO3-delta. Single crystalline films grown by pulsed-laser deposition are fairly insulating below 300 K when having x >= 0.6, while x < 0.6 films exhibit electronic conduction accountable with a variable-range hopping. Room temperature conductivity has a maximum value of 20 Omega(-1) cm(-1) at x similar to 0.2. Hall measurements reveal that the density of the carriers varies as x(1-x) per Ti site up to x similar to 0.35, apparently indicating that La3+ donates one electron to a remaining Ti site. The results are discussed in comparison with the electronic properties of LaySr1-yTiO3 films in terms. of different carrier localization mechanisms.

We report an adjustable saturable absorber based on vertically aligned single-walled carbon nanotubes (SWNTs). Using the low-temperature alcohol catalytic chemical vapor deposition (CVD) method, high-quality vertically aligned SWNTs were directly synthesized onto quartz substrates. The saturable absorption is adjustable by changing the decline angle of the substrate. We applied it as a mode-locker in the passively mode-locked fiber lasers, and optimized the operation by declining the vertically aligned SWNT sample.

Orbital excitations in orbital-ordered transition metal oxides are investigated theoretically and experimentally. Characteristic differences in the collective orbital excitations, termed orbital waves, between the eg and t2g systems are clarified. As a probe to detect the orbital excitations, the scattering processes for the Raman scattering and the resonant and non-resonant inelastic x-ray scatterings are proposed and their scattering cross-sections are calculated. The orbital excitations in hole-doped and undoped manganites are examined experimentally by using resonant inelastic x-ray scattering. The obtained experimental results are compared with the theoretical calculations.

X-ray diffraction study of the irreversible structural transition of the orthorhombic crystal to the face centered cubic crystal at high temperatures. The most remarkable feature of the transition is that the fcc crystal has some preferred orientation relative to the pristine orthorhombic crystal.

Synchrotron x-ray measurements were done on the charge ordered state of La1-x Sr x MnO3 (x∼0.12). In accordance with previous neutron diffraction study, super-lattice reflections which double the b-axis were observed. From the extinction rule of the super-lattice reflections, layer-type charge ordering pattern is plausible. Temperature dependence of the super-lattice peaks might indicate that a certain kind of competition exists in this system.

Hole-doped lanthanum manganites La1-x Sr x MnO3 have been revisited since the discovery of colossal magnetoresistance (CMR). In this system, orbital as well as spin and charge degrees of freedom have attracted much attention. However, direct observation of orbital ordering (OO) is very difficult and there have been few experiments. Recently, Murakami et al. [Phys. Rev. Lett. 80 (1998) 1932, Phys. Rev. Lett. 81 (1998) 582] observed the azimuthal-angle dependence of OO superlattice peaks in La0.5Sr1.5MnO4 and LaMnO3 by resonant x-ray diffraction, which is sensitive to the anisotropy of the structure factor. It is also known that the OO peak changes the polarization of photons from σ to π', which was also observed by Murakami et al. in LaMnO3. We confirmed that the (0 3 0) reflection of La0.88Sr0.12MnO3 is an OO superlattice peak using synchrotron resonant x-ray diffraction, and then carried out polarization analysis of the OO superlattice peak. While the azimuthal-angle dependence of (0 3 0) shows a clear two-fold dependence, the polarization dependence is somewhat obscure. We found that the peak consists of two parts, one of which shows a σ→π' polarization and the other shows a σ→σ' behaviour. We speculate the latter is an extrinsic contamination, though the origin is unknown.

A simultaneous measurement of susceptibility and spontaneous magnetization of a S =5/2 quadratic Heisenberg antiferromagnet with weak canting interaction, Mn(HCOO) 2 ·2H 2 O has been made at exact zero field in the immediate neighbourhood of T N . The critical exponents γ of the staggered susceptibility above T N and β of the spontaneous staggered magnetization below T N are derived to be 1.7±0.1 and 0.31±0.02, respectively in the same temperature range \(5\times10^{-4}{\lesssim}{\varepsilon}({=}|T/T_{\text{N}}{-}1|){\lesssim}1\times10^{-2}\). Such characteristic critical phenomena asymmetric against T N look apparently inconsistent with the scaling law and the universality in the conventional sense.

We present a new technique to synthesize high stage graphite intercalation compounds of low vapor-pressure elements such as rare earth metals (RE). The technique consists of two processes, (1) the co-intercalation of alkali-metal (AM) and RE, in which the stage is mainly controlled by vapor pressure of AM, and (2) the following de-intercalation of AM from the compound, in which the preferential removal of AM results in a high stage RE_GIC. We first obtained stages 2, 3 and 4 Eu- and stage 2 Sm-GICs. However an intercalant layer is composed of a mixture of RE and residual AM; i.e. the in-plane composition x in Eu x K 1−x -GIC was less than 0.75. The temperature dependence of magnetization of stage 3 Eu 0.75 K 0.25 -GIC shows two anomalies at T c 1 = 30 K and T c 2 = 80 K. While at T > T c2 it obeys the Curie-Weiss law with ⊗ = −15K, the magnetization process at T c1 shows remarkable metamagnetism which resembles that of stage 1 EuC 6 . The magnetic anomaly at T c2 is unique to high stage Eu compounds.

The three-dimensional Navier-Stokes equation is solved numerically by the spectral method with 340 3 modes starting from a high-symmetric flow which has a few Fourier components at lower wavenumbers. Kolmogorov's power form of the energy spectrum, E ( k , t )= A e( t ) 2/3 k -5/3 with A ≈2.0 is observed over almost one decade of the wavenumbers after the enstrophy reaches the maximum value. The Kolmogorov constant A is preserved, though the inertial subrange becomes narrower, in the subsequent decay period during which the microscale Reynolds number decreases from 150 to 70.

The characteristic temperature dependence of magnetic heat capacities C m of XY ferromagnetic spin systems in one and two dimensions has been observed in CsNiF 3 and graphite-CoCl 2 , respectively. The value of C m of CsNiF 3 has been shown to depend linearly on temperature T at low temperatures, and reproduced by the theoretical values for an XY ferromagnetic chain with the reported value of exchange constant J / k B =11.8 K and with spin value S =1. While, in the CoCl 3 compound C m has been found to obey C m = m ( J ) T 2 which agrees with the spin wave theory for an XY ferromagnet in two dimensions with J / k B =9.7 K. The thermal behaviour of these compounds reflects magnetic excitations intrinsic to the XY system, making a typical contrast with the case for the Heisenberg system.

Second harmonic resonance between two marginally unstable modes is investigated in the Kelvin-Helmholtz flow. Coupled amplitude equations are obtained which depend on both time and space. Numerical integrations of the equations without spatial dependence reveal that the “explosive” instability takes place, in which both two modes grow rapidly.

The N-breather solutions to the Boussinesq (-Type) equation: u t t - p u x x -6 q ( u 2 ) x x - q u x x x x =0, where p =±1, q =±1 and their existence conditions are presented. It is shown that they are linearly unstable by using the growing-mode solutions, which affect only the phase shift to the breathers as time approaches infinitely.

Dynamical aspects of magnetic ordering in CoCI 2 -graphite intercalation compounds (GIC) were examined by complex AC susceptibility X * (ω) measurements at very low frequencies, down to the sub-millihertz region. The nearly independent feature of the imaginary part X '' on the measuring frequency ω has revealed the first direct finding of a 1/ω-type fluctuation spectrum in regular magnetic systems, on the basis of the fluctuation-dissipation theorem. The origin of the nonlinear fluctuation is discussed, taking the characteristic lattice structure into account.