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We report x-ray scattering studies of the $c$-axis lattice parameter in ${\mathrm{Ca}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ as a function of temperature and magnetic field. These structural studies complement published transport and magnetization data, and therefore elucidate the spin-charge-lattice coupling near the metal-insulator transition. Strong anisotropy of the structural change for field applied along orthogonal in-plane directions is observed. Competition between a spin-polarized phase that does not couple to the lattice and an antiferromagnetic metallic phase that does gives rise to a rich behavior for $\mathbf{B}\ensuremath{\Vert}b$.

We investigated the electronic structures of the two-dimensional layered perovskite ${\mathrm{Sr}}_{2}M{\mathrm{O}}_{4}$ ($M=4d$ Ru, $4d$ Rh, and $5d$ Ir) using optical spectroscopy and polarization-dependent O $1s$ x-ray absorption spectroscopy. While the ground states of the series of compounds are rather different, their optical conductivity spectra $\ensuremath{\sigma}(\ensuremath{\omega})$ exhibit similar interband transitions, indicative of the common electronic structures of the $4d$ and $5d$ layered oxides. The energy splittings between the two ${e}_{g}$ orbitals, i.e., ${d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ and ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$, are about $2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, which is much larger than those in the pseudocubic and $3d$ layered perovskite oxides. The electronic properties of the ${\mathrm{Sr}}_{2}M{\mathrm{O}}_{4}$ compounds are discussed in terms of the crystal structure and the extended character of the $4d$ and $5d$ orbitals.

We present detailed energy dispersions near the Fermi level on the monolayer perovskite ruthenate ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$, determined by high-resolution angle-resolved photoemission spectroscopy. An orbital selectivity of the kink in the dispersion of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ has been found: A kink for the Ru $4{d}_{xy}$ orbital is clearly observed, but not for the Ru $4{d}_{yz}$ and $4{d}_{zx}$ ones. The result provides insight into the origin of the kink.

Muscle atrophy is common in the elderly. However, the etiologic role of muscle atrophy associated with osteoarthritis of the knee has not been studied in detail. We assessed the association between age-related muscle atrophy around the knee joint and incident radiographic osteoarthritis of the knee. Twenty-one women in their thirties and 17 women in their sixties participated. They had no history, symptoms, or objective findings of any knee problems, and none of the participants was limited in performing daily activities. Radiographs of the knee joint were graded for the presence of osteoarthritis, and the cross-sectional imaging around the knee joint was carried out using computed tomography. Incident radiographic osteoarthritis was observed in 6 of the 17 women in their sixties. Quadriceps-dominant muscle atrophy was marked in the elderly women with radiographic osteoarthritis. In a multivariate analysis, the risk of incident radiographic osteoarthritis of the knee was significantly increased among women with a higher hamstrings/quadriceps cross-sectional area ratio. The results suggest the possibility that age-related quadriceps-dominant muscle atrophy may play a role in the pathogenesis of osteoarthritis of the knee.

We report an observation of two-dimensional incommensurate magnetic fluctuations in the layered metallic perovskite ${\mathrm{Sr}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}.$ The wave vectors where the magnetic fluctuations are strongest are different from those observed in the superconducting single layer ruthenate ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ and appear to be determined by Fermi surface nesting. No antiferromagnetic ordering is observed for temperatures down to 1.5 K. For temperatures $T\ensuremath{\gtrsim}20\mathrm{K},$ the fluctuations become predominately ferromagnetic. Our inelastic neutron scattering measurements provide concrete evidence of the coexistence of competing interactions in ${\mathrm{Sr}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ and of the low-energy scale of the fluctuations.

Temperature dependence of the specific heat was measured on a single crystal of UNiGa in magnetic fields. The value γ =40.9 mJ/mol K 2 does not change with the field-induced transition. The magnetic entropy is larger in the high-field (ferromagnetic) state (0.55× R In2) than in the AF ground state (0.50× R In2). Thermodynamic analysis shows that the high-field state is a true ferromagnetic state.

We present the first systematic study on polycrystalline Sr2MoO4 as an electronic analogue to the spin-triplet superconductor Sr2RuO4. The Pauli paramagnetic susceptibility and metallic behaviors of specific heat and electrical resistivity have been observed. The density of states at the Fermi level D(EF) deduced from the results is about three times smaller than that of Sr2RuO4. Any indication of superconductivity intrinsic to Sr2MoO4 has not been observed down to 25 mK, which may correspond to the smaller D(EF). We discuss the origin of the difference in electronic states between Sr2MoO4 and Sr2RuO4., Comment: 4 pages, 6 figures, to be published in J. Phys. Soc. Jpn. 69, No.10 (2000)

High-field ESR measurements of cubic spinel GeCo2O4 single crystals have been performed using the pulsed magnetic field up to 16 T in the temperature range from 300 K to 1.8 K. Dynamical resonance shifts due to antiferromagnetic ordering were observed. New AFMR modes appear below 3 K. High-field ESR measurements reveal complicated phase structures and field-induced magnetic phases below TN, suggesting new temperature field phases.

We studied magnetic properties of Ge-based spinel oxides Ge(Fe1−xCox)2O4 to verify the frustration effect. We discovered that the spin-glass-like behavior in Ge(Fe1−xCox)2O4 exists in 0 ≤ x ≤ 0.9, and coexists with the antiferromagnetic order in 0.1 ≤ x ≤ 0.9. Taking into account the coexistence of spin molecular excitations (frustration effect) and antiferromagnetic order in GeCo2O4 (x = 1), the spin-glass-like behavior coexisting with the antiferromagnetic order in Ge(Fe1−xCox)2O4 might be attributed to the freezing of the spin molecules by the substitution of Fe for Co.

We have investigated the electronic structures of the parent compound of an iron chalcogenide superconductor TlFe2Se2 by bulk-sensitive photoemission spectroscopy (PES). Valence-band PES demonstrates the energy gap opening at the Fermi level due to the shift of Fe 3d state to the higher binding energy side as compared to the calculated density of states, being consistent with the insulating behaviour in transport measurements.

In MgV2O4 with normal spinel structure (AB2O4), there is magnetic frustration of V3+ (3d2+) ions located on B-sites, if an antiferromagnetic interaction among B-site spins is essential for its magnetism. The excess Mg substituted materials such as Mg1+xV2−xO4, may construct isolated magnetic triangular lattices, because some of B-sites forming magnetic tetrahedral lattice are substituted by non-magnetic Mg ions, while the normal spinel MgV2O4 contains tetrahedral magnetic ion networks. Here, we have succeeded in growing single crystals of Mg–V–O system spinel oxide by conventional floating-zone method. The valence numbers and abundance ratio of V ions in the single crystal were estimated by wavelength-dispersive X-ray fluorescence analysis and X-ray photoelectron spectroscopy analysis. Although the composition ratio was Mg:V = 1:2, a small amount of Mg and V ion partly replace each other between A- and B- sites in this crystal. The composition formula is described as (Mg1−xVx)(V2−xMgx)O4. The single crystal shows magnetic transition at around 12 K and large negative antiferromagnetic Weiss temperature about −840 K, and the frustration parameter f = 70 estimated by those temperatures. This result suggests the existence of strong magnetic frustration in our material.

Ultrasound velocity measurements of the cubic spinel GeCo2O4 in the single crystal have been performed for the investigations of shear and compression moduli. The shear moduli reveal the absence of Jahn-Teller activity despite the presence of the orbital degeneracy in the Co2+ ions. This Jahn-Teller inactivity indicates that the intersite orbital-orbital interaction is much stronger than the Jahn-Teller coupling. The compression moduli reveal that the dominant path of the exchange interactions for the antiferromagnetic transition lies in the [111] direction. This exchange-path anisotropy is consistent with the antiferromagnetic structure with the wave vector q ? [111], suggesting the presence of bond frustration among several ferromagnetic and antiferromagientic interactions. In the JT-inactive condition, the bond frustration can be induced by geometrical orbital frustration of t2g-t2g interaction between the Co2+ ions which can be realized in the pyrochlore lattice of the high spin Co2+ with t2g -orbital degeneracy. In GeCo2O4, the tetragonal elongation below TN releases the orbital frustration by quenching the orbital degeneracy.

Transition metal oxides with spinel crystal structure exhibit intriguing and non trivial magnetic phenomena owing to magnetic frustration between spins having antiferromagnetic coupling interaction on triangle or kagome lattice. GeCo2O4(GCO) and GeNi2O4(GNO), which belong to above category, are very rare normal spinels containing Ge ion. Both reveal antiferromagnetic-like phase transitions at 20 K and 12 K, respectively. According to previous neutron and x-ray diffraction measurements, GNO keeps its cubic structural symmetry down to 2 K which is not natural because such a magnetic transition tends to associate with symmetry breaking structural transitions. In order to know whether the structural transition or symmetry change occur or not at the magnetic transition in detail, convergent beam electron diffraction measurements is employed for the compounds.

Cubic spinel GeNi2O4 and GeCo2O4 compounds exhibit field-induced magnetic anisotropy below the antiferromagnetic transition temperature. GeNi2O4 has two antiferromagnetic like transitions at 12.1 K and 11.4 K. Structural phase transitions (PT) which may lower the symmetry and relief frustration of magnetic spins are expected at the temperatures. However, this cubic material does not undergo a structural PT. On the other hand, GeCo2O4 has a structural PT from high-temperature cubic symmetry to low-temperature tetragonal one at the temperature. Although GeCo2O4 demonstrates antiferromagnetic ordering, derived Weiss temperature is ferromagnetic (11.9 K). In order to understand those intriguing ground states in detail, we have measured AC susceptibility below 1 K. The results show there are no other phase transitions above 150 mK for both compounds.

We present detailed energy dispersions near the Fermi level along the high symmetry line GammaX on the monolayer and bilayer strontium ruthenates Sr2RuO4 and Sr3Ru2O7, determined by high-resolution angle-resolved photoemission spectroscopy. A kink in the dispersion is clearly shown for the both ruthenates. The energy position of the kink and the slope in the low-energy part near the Fermi level are almost identical between them, whereas the dispersion in the high-energy part varies, like the behavior of the kink for the cuprate superconductors.

We investigated a method for obtaining a sintered bulk sample of single-phase Sr2MoO4, which has recently increased in importance due to its similarities to superconducting Sr2RuO4. We discovered that with the aid of Ti2O3 as a p(O2) buffer, high-purity Sr2MoO4 is successfully synthesized in a sealed tube. We confirmed the space group and determined the exact elemental composition of the compound in order to establish its stoichiometry. The guideline for the rational choice of a p(O2)-buffer material is discussed., Comment: 4 pages, 4 figures

The procedure for predicting digestive enzyme stability in the solid state was further investigated by utilizing the Weibull distribution function, which needs two mathematically meaningful parameters, m and k. These parameters could be estimated by graphic calculation. If the parameter m is independent of temperature, the Arrhenius plots of (1/m) 1nk versus 1/T are linear since k1/m is proportional to the inactivation rate constant. The parameter k could be estimated by extrapolating to the desired temperature in the Arrhenius plots and the activation energy could be determined from the slope of this line. These parameters, m and k, made it possible to predict the inactivation ratio of enzymes in the solid state. By comparing the predicted value of the inactivation ratio with the observed value under controlled conditions, it was shown that the proposed method is accurate and useful for studies on enzyme stability in the solid state.