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Field-orientation dependences of the magnetization M ( H ,θ) and the ordering temperature T A ( H ,θ) of the low-field phase (A-phase) of the filled skutterudite compound PrFe 4 P 12 have been studied in detail at low temperatures down to 0.3 K, by means of angle-resolved magnetization measurements. Both M ( H ,θ) deep inside the A-phase and T A ( H ,θ) show a smooth angular variation with a cubic anisotropy when H is rotated within the (001) and (1\bar10) planes. The results strongly suggest that the order parameter of the A-phase is of scalar (Γ 1 + ) type which, together with the (1,0,0) ordering vector, preserves the cubic symmetry. The magnitude of the cubic anisotropy term in the magnetization in the ordered state at low temperatures is found to vary with H and exhibits a sign reversal at ∼2.3 T.

We have investigated the thermoelectric power (TEP) and Hall coefficient ( R H ), along with the field dependence of Hall resistivity (ρ H ) and magnetoresistance (MR) in single crystals of CeCu 5.9 Au 0.1 and CeCu 6 . In both compounds, R H is highly anisotropic with respect to the field direction below ∼10 K. For H ∥[001], a negative minimum in ρ H and a positive MR peak grow at low temperatures near 1.7 T, where a metamagnetic-like anomaly was reported for CeCu 6 . The Au substitution induces drastic changes in R H depending on the magnetic field direction, which is discussed in correlation with the predicted change in the Fermi surface across the quantum critical point. In CeCu 5.9 Au 0.1 , an unexpectedly large positive MR has been found at low temperatures and in low fields; its origin is discussed in comparison with the Hall resistivity. For all the principal axes, the Au-substitution effect on TEP is minor in both magnitude and anisotropy down to ∼1.5 K, suggesting no essential change in the elect...

This review presents a summary and evaluation of the experimental properties of unconventional superconductivity in PrOs 4 Sb 12 . After a brief introduction of filled skutterudites, we argue that the normal-state properties of PrOs 4 Sb 12 are quite different from ordinary heavy-fermion superconductors, in the sense that the 4 f -electrons seem to be well localized even at low temperatures where the superconductivity appears. This is reflected in the existence of a field-induced antiferro-quadrupole ordering of Pr 4 f -electrons. It is shown that the 4 f collective excitations can be described as quadrupolar excitons . Their strong temperature dependence in close correlation with the superconductivity suggests a conjecture that the superconducting mechanism may involve quadrupolar-exciton-mediated pairing of some kind. Although the structure of the superconducting order parameter is far from conclusive, outstanding experimental observations reported to date reveal the uniqueness of the unconventional sup...

We have measured the resonant-inverse photoemission spectra for PrSn 3 , PrCo 2 , and PrAg in the Pr 4 d –4 f excitation region. Similar to the case of Ce compounds, the spectra strongly depend on the energy of the incident electron. We determined the “on-resonance” and “off-resonance” energies as 124 and 115 eV, respectively, and these energies are common to all the Pr compounds. The dependence of the spectra on the energy of the incident electron is well explained by the calculation based on the single-impurity Anderson model considering the bulk and surface components. A clear shoulder near the Fermi energy was observed in the on-resonance spectra for PrSn 3 and PrCo 2 , and this shoulder is assigned to the f 2 final-state peak. The result of the analysis shows that the Pr 4 f electron in PrSn 3 and PrCo 2 has more itinerant charactaristics compared with that in PrAg, which is consistent with the result of the photoemission spectroscopy experiments.

The X-ray absorption spectra of the heavy fermion compounds SmFe 4 P 12 and SmOs 4 Sb 12 have been measured near the Sm L 3 -edge at selected temperatures below 300 K. The spectra show the valence of Sm ions in SmFe 4 P 12 to be trivalent between 14 and 300 K with no significant temperature dependence. In contrast, that in SmOs 4 Sb 12 is 2.83 at 300 K and shows a significant decrease below 150 K, indicating an important role of the nonmagnetic Sm 2+ ions in the heavy fermion state that are insensitive to an applied magnetic field.

We performed muon spin relaxation measurements on randomly aligned single-crystalline samples of SmRu 4 P 12 down to 0.02 K to investigate static and dynamical magnetic properties in low fields. Th...

Inelastic neutron scattering measurements at different temperatures were performed on single crystals of CeOs4Sb12. The room temperature phonon dispersion curves along principal axes [0 1 1] and [1 0 0] were obtained.

We report the results of NQR (nuclear quadrupole resonance) study on SmRu 4 P 12 , one of a few candidates for materials showing octupolar ordering. In this study, we firstly succeeded in observing the 101 Ru-NQR signal in filled skutterudite compounds R Ru 4 P 12 ( R : rare earth). A single 101 Ru-NQR signal splits into two resonance lines, having intensity ratio of 3:1, just below the metal–insulator ( M – I ) transition temperature of 16.5 K. This result gives convincing evidence for symmetry lowering in the ordered state of this compound, namely the cubic I m \bar3 space group for the filled skutterudite compounds is lowered to the trigonal R \bar3. The model of the ordered structure characterized by a wave vector q =(1,0,0) satisfactorily explains the observed phenomena in the present study and the M – I transition in this compound.

We have performed 31P nuclear magnetic resonance (NMR) experiments on the filled skutterudite compound PrFe4P12 to investigate the exotic ordered phase at low temperatures and low magnetic fields. Analysis of the NMR line splitting in the ordered phase indicates that totally symmetric (\Gamma_1-type) staggered magnetic multipoles are induced by magnetic fields. This is incompatible with any type of quadrupole order at zero field. We conclude that the ordered phase has broken translational symmetry with the wave vector Q=(1,0,0) but the Th point symmetry at the Pr sites is not broken by the non-magnetic \Gamma_1-type order parameter., Comment: 4 pages, 6 figures, some typos corrected, published version

Inelastic neutron scattering was performed on both poly- and single-crystalline samples to study the lattice dynamics of the Ce-filled antimonide skutterudite. For powder samples, no well-defined extra phonon excitation peak, which was reported to indicate a local Einstein oscillating mode, was detected in the low-energy region of the vibrational density of states within the experimental accuracy. However, a coherent phonon was clearly observed in single crystals at different temperatures. The dispersion curves were measured along two symmetry axes[0 1 1] and [1 0 0] at room temperature and compared with theoretical calculation by Feldman et al. [Phys. Rev. B 73, 014306 (2006)] using the model of local density approximation.

We report 123 Sb nuclear quadrupole resonance (NQR) measurements of the filled skutterudite heavy-fermion superconductor PrOs 4 Sb 12 under high pressures of 1.91 and 2.34 GPa. The temperature dependence of NQR frequency and the spin-lattice relaxation rate 1/ T 1 indicate that the crystal-electric-field splitting Δ CEF between the ground state Γ 1 singlet and the first excited state Γ 4 (2) triplet decreases with increasing pressure. The 1/ T 1 below T c = 1.55 K at P = 1.91 GPa shows a power-law temperature variation and is proportional to T 5 at temperatures considerably below T c , which indicates the existence of point nodes in the superconducting gap function. The data can be well fitted by the gap model Δ(θ) = Δ 0 sin θ with Δ 0 = 3.08 k B T c . The relation between the superconductivity and the quadrupole fluctuations associated with the Γ 4 (2) state is discussed.

Experiments on the NMR signal splitting of 31 P are reported for the low temperature phase of PrFe 4 P 12 , whose nature has been controversial. The observed NMR signal splitting is consistent with...

We report the first successful results on the de Haas-van Alphen (dHvA) experiments of the superconducting LaFe 4 P 12 and the ferromagnetic NdFe 4 P 12 . Their Fermi surfaces are found to be similar except for the splitting of the dHvA branches for NdFe 4 P 12 due to the ferromagnetic exchange interaction.

The field versus temperature phase diagram of the magnetic superconductor YbPd 2 Sn has been determined by electrical resistivity. AC magnetic susceptibility and specific heat. The upper critical field B c2 is found to be small (0.04 T at T → 0). Reentrant behavior in the magnetic field implies competition between the superconductivity and antiferromagnetic short-range correlation. Based on a Schottky peak found in the specific heat for B ⩾ 0.3T, the crystalline-field ground state of Yb 3+ is confirmed to be Γ 7 .

The phonon dynamics of filled skutterudite CeRu4Sb12 have been studied at room temperature by inelastic neutron scattering. Optical phonons associated with a large vibration of Ce atoms are observed at a relatively low energy of E = 6 meV, and show anticrossing behavior with acoustic phonons. We propose that the origin of the low lattice thermal conductivity in filled skutterudites can be attributed to intensive Umklapp scattering originating from low-lying optical phonons. By an analysis based on a Born-von Karman force model, the longitudinal force constants of the nearest Ce-Sb and Ce-Ru pairs are estimated to be 0.025 mdyn/A, while that of the nearest Ru-Sb pair is estimated to be 1.4 mdyn/A, indicating that the Ce atoms are bound very weakly to the surrounding rigid RuSb6-octahedron cages., Comment: 4pages, 5 figures, J. Phys. Soc. Jpn. (2006) in press

We report the first X-ray diffraction experiments of PrFe 4 P 12 under high pressure. We discovered a symmetry lowering from cubic to orthorhombic or lower at the metal–insulator transition temperature, accompanied by a jump in the lattice constant, which indicates a first-order phase transition. The superlattice reflections at q =(1,0,0) observed in the low-pressure nonmagnetic ordered phase are found to disappear in the insulating phase. The temperature dependence of the lattice constant and the absence of the superlattice reflections are well explained by taking into account an antiferromagnetic ordering.

We have carried out X-ray absorption spectroscopy, 149 Sm nuclear resonant forward scattering, and 99 Ru Mossbauer spectroscopy of SmRu 4 P 12 . The X-ray absorption spectra indicate that the Sm ions are trivalent up to 14 K. The quantum beats due to magnetic dipolar ordering are observed at 4.5 K in 149 Sm nuclear resonant forward scattering. The temperature dependence of time-integrated intensity in 149 Sm nuclear forward scattering suggests that the magnetic dipolar ordering occurs just below the metal–insulator transition temperature. No significant changes in the parameters are observed between 77 and 5 K in 99 Ru Mossbauer spectroscopy. The present result suggests a magnetic ordering accompanied by a magnetic dipole moment at the metal–insulator transition temperature in SmRu 4 P 12 in spite of the proposal of the magnetic ordering accompanied by a T β -type octupole.

The ground state and physical properties of CeOs4Sb12 are primary determined by the competition among three types of energies which are all related to interactions of the Ce3+ 4f electron with the lattice and the spin lattice, i.e., the Kondo interaction, the Ruderman-Kittel-Kasuya-Yosida interaction, and the crystal field energy. In this work, inelastic neutron scattering experiments were performed on CeOs4Sb12 powder samples at low temperatures in order to investigate the magnetic interactions, the origin of unusual physical properties and, in particular, to elucidate the ground state of crystal field splitting. The result indicates that, within the accuracy of experimental error, no well defined crystal field effect could be detected around the expected energy of 28.2meV as computed on the basis of a localized Ce3+ state model. That means that other causes are responsible for the deviation of inverse susceptibility from the linear Curie law at low temperatures and that further studies are necessary to ...

We study the superconducting gap of the filled skutterudite superconductor LaRu 4 P 12 (transition temperature T c =7.2 K) using a newly developed sub-meV resolution photoemission spectrometer with a vacuum-UV laser as a light source. The result at 4.8 K shows the opening of a superconducting gap, whose spectral shape is well explained with an isotropic s-wave Dynes function using a gap size of 1.3 meV. This corresponds to the reduced gap 2Δ(0)/ k B T c of 4.2. The temperature dependence of the superconducting gap shows fairly good agreement with the conventional BCS theory. The present results are consistent with those of a moderately strong-coupling and isotropic s-wave superconductor.

We have performed an epithermal neutron scattering experiment along with magnetic susceptibility, resistivity, Hall effect, X-ray diffraction measurements on single crystals grown for the first time. The primary crystal structure was classified into the same structure as that of Yb 3 Rh 4 Sn 13 with the space group P m \bar3 n . However the crystal distortion characterized by (1/2, 1/2, 0) was observed at room temperature by X-ray diffraction. The magnetic susceptibility and resistivity showed an anomaly at 10 K indicating a magnetic phase transition. The epithermal neutron diffraction clarified that an antiferromagnetic order with the propagation vector (100) exist below 10 K. Overall features of transport properties in Gd 3 Ir 4 Sn 13 are similar to those in La 3 Ir 4 Sn 13 .

We report the results of the low-temperature dc magnetization measurements of PrOs 4 Sb 12 under hydrostatic pressures up to 1.45 GPa. The pressure effect on the temperature dependence of magnetiza...

Temperature dependence of Ce 4f magnetic moment was measured on Ce x La 1- x Ni ( x =1.0,0.9,0.8,0.7,0.4) using the 3d–4f core excitation magnetic circular dichroism (MCD). The bulk magnetic susceptibilities of these samples were also measured with SQUID. The two results were largely different at temperatures lower than “coherent Kondo temperature”, T K . The MCD results showed the Curie–Weiss behavior but the estimated negative Weiss temperatures are remarkably lower than T K , except the case of x =0.4 showing a positive Weiss temperature but not exhibiting the Kondo effect. It is suggested that the MCD results reflect a local spin-singlet effect with smaller binding energy, while the bulk Kondo temperatures are raised due to coherent hybridization between 4f and ligand states.

We report the results of 121,123 Sb-nuclear quadrupole resonance (NQR) and 139 La-NMR measurements on a filled skutterudite antimonide LaFe 4 Sb 12 in order to investigate the magnetic properties at low temperatures from a microscopic point of view. The nuclear spin–lattice relaxation time T 1 of Sb nuclei deviates from the relation T 1 T = constant above 4.2 K, where 1/ T 1 T has a Curie–Weiss temperature dependence 1/ T 1 T = C /( T +θ) with θ∼30 K. The temperature dependence of the Knight shift of 139 La nuclei, which is related to the susceptibility at q = 0, is scaled to that of 1/ T 1 T above 40 K. This relation strongly suggests that ferromagnetic fluctuations are predominant in LaFe 4 Sb 12 . We also point out that LaFe 4 Sb 12 is situated close to the ferromagnetic instability due to the small Weiss temperature in the Curie–Weiss behavior of 1/ T 1 T and the Knight shift.

We found a clear evidence of anisotropic superconducting gap in the low-temperature specific heat of high-quality CeCo 2 single crystals. The electronic specific-heat jump at T c is reduced ( ΔC e / γT c = 0.85) compared to the value of 1.43 and C e varies approximately as T 2 at low temperatures of T ≪ T c .

We have measured the temperature dependence of the electrical resistivity, thermoelectric power and Hall coefficient of CeOs2 in two deferent crystallographic structures C14 and C15. We observed clear differences in all the transport properties between the two phases. The C14 phase behaves like a normal metal with a stable Ce4+, while the C15 exhibits various features characteristic of valence fluctuating compounds. This fact explains why only the C14 becomes superconductive.

To investigate the origin of giant magnetoresistance in UNiGa, we have measured the field dependence of specific heat in the field B//c-axis. The electronic specific heat coefficient γ, being 48 mJ/K2mole in high-field ferromagnetic (F) phase, decreases by 10% in low-field antiferromagnetic (AF) phase. This is the first direct evidence of a superzone-gap formation suggesting that the large resistivity in AF phase is caused at least partly by the gap. The nuclear specific heat mainly due to Ga nuclear hyperfine field is observed.

We report the first measurements of Hall effect on non-coupled type multilayers with V-groove microstructure for current-at-an-angle-to-plane (CAP) geometry. The field dependence of extraordinary Hall resistivity (ρHM) shows a clear difference between CAP and current-in-plane (CIP) geometries at low fields. In contrast,\(\rho _{\rm H} ^{M_S } \) at saturation field are almost same despite the large difference in the resistivity (ρ) between two the geometries. We also report results on Fe/Cr(110) superlattices with facet microstructure for comparison.

The Dispersion mechanism of highly loaded coal-water mixture (CWM) in the presence of a polyelectrolyte additive was investigated. Two important factors have been found : the ability of the additive to apply a sufficient electric repulsive force to the coal particles, and an appropriate affinity of the additive to the coal surface.

The de Haas-van Alphen amplitude of branch d in CeIn3 is reduced with oscillation by three orders of magnitude when the field is tilted from 〈100〉 to 〈110〉 in the {100} plane. This is explained by considering the angular dependence of the cyclotron mass and the electron spin g-factor.

We have observed the de Haas-van Alphen oscillation of YbGa 2 . It is a semimetal and Fermi surfaces consist of closed electron and hole surfaces.

CeFe4P12 is a non-magnetic semiconductor which might include both “strongly correlated” and “weakly correlated” systems, also being a reference material to investigate the interesting property of LaxCe1-xFe4P12. In order to check the above expectation we tried to measure small MCD signals in the Ce 3d-4f and Fe 2p-3d excitation regions. It was found that the MCD signal intensity per atom at Fe atomic site is much smaller than that in Ce atomic site, suggesting that the empty Fe 3d states would be a “weakly correlated” or a very itinerant system. It is also suggested that the MCD spectrum of Ce 3d-4f excitation region reflects some polarization induced by the externally applied magnetic field both in the ground and the excited states.

Temperature and magnetic field dependence of the resistivity of Zr-N sputtered films have been measured. The characteristics of Zr-N film, that they can be divided into two groups by the ratio of the resistance at helium and room temperatures, have been precisely investigated. There are marked differences in both the temperature dependence of resistance and in the magnetoresistance between the two groups. The temperature dependence of magnetoresistance of the films has been discussed within the framework of Anderson localization. The origin of magnetoresistance was also discussed.

Regulation of delayed rectifier-type K(+) channels (Kv-channels) by glucose was studied in rat pancreatic beta-cells. The Kv-channel current was increased in amplitudes by increasing glucose concentration from 2.8 to 16.6mM, while it was decreased by 2.8mM glucose in a reversible manner (down-regulation) in both perforated and conventional whole-cell modes. The current was decreased by FCCP, intrapipette 0mM ATP or AMPPNP. Glyceraldehyde, pyruvic acid, 2-ketoisocaproic acid, and 10mM MgATP prevented the down-regulation induced by 2.8mM or less glucose. The residual current after treatment with Kv2.1-specific blocker, guangxitoxin-1E, was unchanged by lowering or increasing glucose concentration. We conclude that glucose metabolism regulates Kv2.1 channels in rats beta-cells via altering MgATP levels.