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A new ternary layered pnictide, Li1−xSn2+xP2, was synthesized by a solid-state reaction and its properties were examined to explore its potential as a multifunctional material. The compound crystallizes in a layered structure in the Rm space group (no. 166) with buckled honeycomb Sn–P layers separated by mixed-occupation Li/Sn layers. Crystal structure analysis by synchrotron X-ray diffraction showed that the substitution degree of Li by Sn is x = 0.38. The local ordering of Li/Sn occupation was demonstrated using 31P nuclear magnetic resonance analysis. The thermal and electrical transport properties are significantly affected by this local ordering. The lattice thermal conductivity of Li1−xSn2+xP2 was found to be relatively low (1.2 W m−1 K−1 at 525 K). The room-temperature electrical resistivity of Li1−xSn2+xP2 was found to be 0.3–0.4 mΩ cm and metallic conductivity was observed down to 0.5 K. First-principles calculations demonstrated that the electronic structure and Fermi energy of Li1−xSn2+xP2 are significantly dependent upon x. Moreover, the electronic structure of Li1−xSn2+xP2 is different from that of the related compound NaSn2As2, which shows a superconducting transition. Electrochemical measurements using a single-particle technique demonstrated the activity of Li1−xSn2+xP2 as an anode material for rechargeable Li-ion batteries.

A new ternary layered pnictide, Li1-xSn2+xP2, was synthesized by a solid-state reaction and its properties were examined to explore its potential as a multifunctional material. The compound crystallizes in a layered structure in the R-3m space group with buckled honeycomb Sn-P layers separated by mixed-occupation Li/Sn layers. Crystal structure analysis using synchrotron X-ray diffraction showed that the substitution degree of Li by Sn (x) is approximately 0.3. Local ordering of Li/Sn occupation was demonstrated using 31P nuclear magnetic resonance analysis. The lattice thermal conductivity of Li1-xSn2+xP2 was found to be relatively low (1.2 Wm−1K−1 at 525 K). The room-temperature electrical resistivity of Li1-xSn2+xP2 was found to be 0.3-0.4 mohm cm and metallic conductivity was observed down to 0.5 K. First-principles calculations demonstrated that the electronic structure and Fermi energy of Li1-xSn2+xP2 are significantly dependent upon x. Electrochemical measurements using a single-particle technique demonstrated the activity of Li1-xSn2+xP2 as an anode material for rechargeable Li-ion batteries.

We report on a systematic study of Hall effect using high quality single crystals of type-II Weyl semimetal WTe 2 with the applied magnetic field B//c . The residual resistivity ratio of 1330 and the large magnetoresistance of 1.5 × 10 6 % in 9 T at 2 K, being in the highest class in the literature, attest to their high quality. Based on a simple two-carrier model, the densities ( n e and n h ) and mobilities ( μ e and μ h ) for electron and hole carriers have been uniquely determined combining both Hall- and electrical-resistivity data. The difference between n e and n h is ~ 1% at 2 K, indicating that the system is in an compensated condition. The negative Hall resistivity growing rapidly below ~ 20 K is due to a rapidly increasing μ h /μ e approaching one. Below 3 K in a low field region, we found the Hall resistivity becomes positive, reflecting that μ h /μ e finally exceeds one in this region. These anomalous behaviors of the carrier densities and mobilities might be associated with the existence of a Lifshitz transition and/or the spin texture on the Fermi surface.

Ce1–xPrxOBiS2 powders and Ce0.5Pr0.5OBiS2 single crystals were synthesized and their structure and superconductive properties were examined by X-ray diffraction, X-ray absorption, electronic resistivity, and magnetization. While PrOBiS2 was found to be in a monoclinic phase with one-dimensional Bi–S zigzag chains showing no superconductive transition above 0.1 K, CeOBiS2 was in a tetragonal phase with two-dimensional Bi–S planes showing zero resistivity below 1.3 K. In the range x = 0.3–0.9 in Ce1–xPrxOBiS2, both monoclinic and tetragonal phases were formed together with zero resistivity up to a maximum temperature of 2.2 K. A Ce0.5Pr0.5OBiS2 single crystal, which showed both zero resistivity and a decrease in magnetization at ∼2.4 K, presented a tetragonal structure. Short Bi–S bonding in flat two-dimensional Bi–S planes and mixed Ce3+/Ce4+ were characteristic features of the Ce0.5Pr0.5OBiS2 single crystal, which presumably triggered its superconductivity.

Recently, we reported the observation of superconductivity at ~0.5 K in a La2O2M4S6-type (M: metal) layered compound La2O2Bi3AgS6, which is a layered system related to the BiS2-based superconductor system but possesses a thicker Bi3AgS6-type conducting layer. In this study, we have developed the La2O2Bi3AgS6-type materials by element substitutions to increase the transition temperature (Tc) and to induce bulk nature of superconductivity. A resistivity anomaly observed at 180 K in La2O2Bi3AgS6 was systematically suppressed by Sn substitution for the Ag site. By the Sn substitution, Tc increased, and the shielding volume fraction estimated from magnetization measurements also increased. The highest Tc (=2.3 K) and the highest shielding volume fraction (~20%) was observed for La2O2Bi3Ag0.6Sn0.4S6. The superconducting properties were further improved by Se substitutions for the S site. By the combinational substitutions of Sn and Se, bulk-superconducting phase of La2O2Bi3Ag0.6Sn0.4S5.7Se0.3 with a Tc of 3.0 K (Tconset = 3.6 K) was obtained.

Electrical resistivity, magnetic susceptibility, and specific heat measurements on single crystals of La$Tr_{2}$Al$_{20}$ ($Tr$ = Ti, V, Nb, and Ta) revealed that these four compounds exhibit weak-coupling superconductivity with transition temperatures $T_{\rm c}$ = 0.46, 0.15, 1.05, and 1.03 K, respectively. LaTi$_{2}$Al$_{20}$ is most probably a type-I superconductor, which is quite rare among intermetallic compounds. Single-crystal X-ray diffraction suggests "rattling" anharmonic large-amplitude oscillations of Al ions (16$c$ site) on the Al$_{16}$ cage, while no such feature is suggested for the cage-center La ion. Using a parameter $d_{\rm GFS}$ quantifying the "guest free space" of the cage-center ion, we demonstrate that nonmagnetic $RTr_{2}$Al$_{20}$ superconductors are classified into two groups, i.e., (A) $d_{\rm GFS} \ne 0$ and $T_{\rm c}$ correlates with $d_{\rm GFS}$, and (B) $d_{\rm GFS} \simeq 0$ and $T_{\rm c}$ seems to be governed by other factors., Comment: 5 pages, 5 figures. To appear in J. Phys. Soc. Jpn

Superconductors with a van der Waals (vdW) structure have attracted a considerable interest because of the possibility for truly two-dimensional (2D) superconducting systems. We recently reported NaSn2As2 as a novel vdW-type superconductor with transition temperature (Tc) of 1.3 K. Herein, we present the crystal structure and superconductivity of new material Na1-xSn2P2 with Tc = 2.0 K. Its crystal structure consists of two layers of a buckled honeycomb network of SnP, bound by the vdW forces and separated by Na ions, as similar to that of NaSn2As2. Amount of Na deficiency (x) was estimated to be 0.074(18) using synchrotron X-ray diffraction. Bulk nature of superconductivity was confirmed by the measurements of electrical resistivity, magnetic susceptibility, and specific heat. First-principles calculation using density functional theory shows that Na1-xSn2P2 and NaSn2As2 have comparable electronic structure, suggesting higher Tc of Na1-xSn2P2 is resulted from increased density of states at the Fermi level due to Na deficiency. Because there are various structural analogues with tin-pnictide (SnPn) conducting layers, our results indicate that SnPn-based layered compounds can be categorized into a novel family of vdW-type superconductors, providing a new platform for studies on physics and chemistry of low-dimensional superconductors., Comment: 15 pages, 5 figures, to be published in Scientific Reports

We have succeeded in growing single crystals of SmIr2Si2 by Sn-flux method. A single-crystal structure determination has revealed that the single crystals have the tetragonal ThCr2Si2- type crystal structure (I4/mmm, #139). The residual resistivity ratio RRR (=ρ300K/ρ2K) is 270, indicating the high quality of the samples. The electrical resistivity shows metallic behavior with slight downward curvature. A kink structure appearing at 37.8K indicates the existence of a phase transition. It is expected that investigations on the magnetism of SmIr2Si2 single crystals will help to understand the strongly-correlated electron physics of “partially magnetically-disordered (paramagnetic)” Sm ions in a magnetically ordered state, suggested recently in SmPt2Si2 [K. Fushiya et al, J. Phys. Soc. Jpn. 83, 113708 (2014)].

We have succeeded in growing SmxLa1-xTa2Al20 single-crystals, and performed electronic transport measurements to investigate the characteristic features of conduction electron scattering relevant to the field-insensitive – logT dependence of the resistivity. We have found that the – logT dependence of the resistivity remains in a Sm-dilute compound with x = 0.01. This finding provides clear evidence for that the – logT dependence is caused by a local single-ion Kondo effect. We have measured magnetoresistance (MR) of SmTa2Al20 up to 14 T and confirmed that the positive MR continues to develop with decreasing temperature even at 0.5K, evidencing a large deviation from Kohler's rule. This fact indicates that strong wave-vector dependence of conduction-electron scattering by 4f electrons still remains at 0.5K in the magnetically ordered state.

High-entropy-alloy-type tellurides M-Te, which contain five different metals of M = Ag, In, Cd, Sn, Sb, Pb, and Bi, were synthesized using high pressure synthesis. Structural characterization revealed that all the obtained samples have a cubic NaCl-type structure. Six samples, namely AgCdSnSbPbTe5, AgInSnSbPbTe5, AgCdInSnSbTe5, AgCdSnPbBiTe5, AgCdInPbBiTe5, and AgCdInSnBiTe5 showed superconductivity. The highest transition temperature (Tc) among those samples was 1.4 K for AgInSnSbPbTe5. A sample of AgCdInSbPbTe5 showed a semiconductor-like transport behavior. From the relationship between Tc and lattice constant, it was found that a higher Tc is observed for a telluride with a larger lattice constant., 9 pages, 4 figures

Superconductivity with exotic properties has often been discovered in materials with a layered (two-dimensional) crystal structure. The low dimensionality affects the electronic structure of materials, which could realize a high transition temperature (Tc) and/or unconventional pairing mechanisms. Here, we report the superconductivity in a layered tin arsenide NaSn2As2. The crystal structure consists of (Sn2As2)2- bilayers, which is bound by van-der-Waals forces, separated by Na+ ions. Measurements of electrical resistivity and specific heat confirm the bulk nature of superconductivity of NaSn2As2 with Tc of 1.3 K. Our results propose that the SnAs layers will be a basic structure providing another universality class of a layered superconducting family, and it provides a new platform for the physics and chemistry of low-dimensional superconductors with lone pair electrons., Comment: 12 pages, 1 table, 3 figures

We have investigated Se substitution effect to superconductivity of an optimally-doped BiS2-based superconductor Eu0.5La0.5FBiS2. Eu0.5La0.5FBiS2-xSex samples with x = 0-1 were synthesized. With increasing x, in-plane chemical pressure is enhanced. For x = 0.6, 0.8, and 1, superconducting transitions with a large shielding volume fraction are observed in magnetic susceptibility measurements, and the highest Tc is 3.8 K for x = 0.8. From low-temperature electrical resistivity measurements, a zero-resistivity state is observed for all the samples, and the highest Tc is observed for x = 0.8. With increasing Se concentration, characteristics of electrical resistivity changes from semiconducting-like to metallic, suggesting that the emergence of bulk superconductivity is linked with the enhanced metallicity. A superconductivity phase diagram of the Eu0.5La0.5FBiS2-xSex superconductor is established. Temperature dependences of electrical resistivity show an anomalous two-step transition under high magnetic fields. Hence, the resistivity data are analyzed with assuming in-plane anisotropy of upper critical field., 23 pages, 16 figures (including 10 supplemental materials), 2 tables as supplemental materials

Sn0.8Ag0.2Te is a new superconductor with Tc ~ 2.4 K. The superconducting properties of Sn0.8Ag0.2Te have been investigated by specific heat measurements under magnetic fields. Bulk nature of superconductivity was confirmed from the amplitude of the specific heat jump at the superconducting transition, and the amplitude is consistent with fully-gapped superconductivity. Upper critical field was estimated from specific heat and electrical resistivity measurements under magnetic fields. The Hall coefficient was positive, suggesting that the Ag acts as a p-type dopant in Sn0.8Ag0.2Te., 11 pages, 5 figures

We measure the electrical resistivity ρ of type-II Weyl semimetal WTe2 using high-quality single crystals for the current I along the a and b crystallographic directions in rotating magnetic fields in the plane perpendicular to the current direction. In zero field, ρ exhibits huge anisotropy and the ratio ρb/ρa develops with decreasing temperature approaching ∼30 at T = 0. A low-T power-law behavior of ρ∝Tn with n = 2.7-2.9 may reflect the characteristic carrier scattering mechanism, probably associated with the strongly T-dependent mobilities, which lead to the sign change in the Hall resistivity. In the Kohler plot, the magnitude of the transverse magnetoresistance (MR) differs by more than two orders of magnitude depending on the I- and B-directions. It also shows clear deviation of MR from the B2 dependence for all the configurations. No singular directions (magic angles) appear in the rotating B measurements.

We report the superconductivity in layered oxychalcogenide La2O2Bi3AgS6 compound. The La2O2Bi3AgS6 compound has been reported recently by our group, which has a tetragonal structure with the space group P4/nmm. The crystal structure of La2O2Bi3AgS6 can be regarded as alternate stacks of LaOBiS2-type layer and rock-salt-type (Bi,Ag)S layer. We measured low-temperature electrical resistivity and observed superconductivity at 0.5 K. The observation of superconductivity in the La2O2Bi3AgS6 should provide us with the successful strategy for developing new superconducting phases by the insertion of a rock-salt-type chalcogenide layer into the van der Waals gap of BiS2-based layered compound like LaOBiS2., Comment: 7 pages, 2 figures; to be published in J. Phys. Soc. Jpn

We have investigated the electrical resistivity under magnetic fields in the itinerant-electron weak ferromagnet LaFe 4 As 12 , in order to clarify the characteristics of spin fluctuations in this material by comparison with the reported typical itinerant-electron ferromagnets. As a common feature to the typical itinerant-electron weak ferromagnets, strong enhancement of negative longitudinal magnetoresistivity was observed near T C , reflecting the suppression of spin fluctuations. As a unique behavior of LaFe 4 As 12 , we found a considerable positive component of the magnetoresistivity above T C .

The low-temperature properties of CeOBiS$_2$ single crystals are studied by electrical resistivity, magnetization, and specific heat measurements. Ce 4f -electrons are found to be in a well-localized state split by crystalline-electric-field (CEF) effects. The CEF ground state is a pure $J_z$ = $\pm$ 1/2 doublet, and excited doublets are located far above. At low temperatures in zero field, we observe pronounced $-\log T$ divergence in the specific heat, revealing the presence of quantum critical fluctuations of 4f magnetic moments near a quantum critical point (QCP). Considering that CeOBiS$_2$ is a nonmetal, this phenomenon cannot be attributed to the competition between Kondo and the Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions as in numerous f-electron-based strongly correlated metals, indicating an unconventional mechanism. We suggest that CeOBiS$_2$ is the first material found to be located at a QCP among geometrically frustrated nonmetallic magnets., 12 pages, 5 figures

Specific heat and transport measurements have revealed an unconventional heavy-fermion (HF) state in SmOs4Sb12 single crystals. The electronic specific-heat coefficient (gamma=0.82 J/K^2mol) and the coefficient (A) of the quadratic temperature dependence of electrical resistivity are largely enhanced, although the ratio A/gamma^2 is reduced from the Kadowaki-Woods ratio of HF materials. Both gamma and A do not show any significant decrease in applied field in contrast with Ce-based HF compounds, suggesting an unconventional origin of the heavy quasiparticles. A weak ferromagnetic ordering sets in below about 3 K, probably originating in the itinerant quasiparticles., Comment: 5 pages, 8 figures. To appear in J. Phys. Soc. Jpn., vol.74 (2005)

The electrical resistivity ρ(T) of Y1−xUxPd3 (x = 0,0.05 and 0.2) and the lattice constants for x = 0 have been measured at high pressure. It is found that the cubic Cu3Au structure is stable up to 12 GPa at room temperature. The Kondo temperature TK was extracted from the ρ(T) curve and it was found that it increases with pressure. A logarithmic temperature dependence characteristic of the Kondo effect was found for x = 0.2 in the temperature range above about 0.5TK. Fermi liquid behaviour in ρ(T) for x = 0.05, i.e., , is observed and its stability at high pressure is discussed. The pressure dependence of the Kondo temperature TK is discussed using the Gruneisen parameters at TK, ΓK. It appears that the values of ΓK are the same for these two compounds (x = 0.05 and 0.2): ΓK = 12. The T-linear behaviour in ρ(T) for x = 0.2, which is characteristic behaviour for non-Fermi liquids, is collapsed by an application of pressure and typical Fermi liquid quadratic temperature dependence recovers at high pressure. From the result for x = 0.2, the power n of the temperature in is determined as 1.0 at ambient pressure and 1.9 at 5.8 GPa. It is pointed out that the hybridization effect due to the application of pressure gives rise to a crossover from a non-Fermi liquid state to Fermi liquid state. But the crossover temperature Tcr shows a pressure dependence different from that predicted by the two-channel Kondo model.

We have measured the electrical resistivity, magnetic susceptibility, high-field magnetization, specific heat and de Haas–van Alphen (dHvA) oscillation of Ce 2 RhIn 8 , together with the dHvA oscillation of La 2 RhIn 8 . In La 2 RhIn 8 we detected three kinds of dHvA branches showing cylindrical Fermi surfaces, which are well explained by the result of FLAPW energy band calculations. The corresponding two dHvA branches were detected in Ce 2 RhIn 8 , indicating that the topology of the Fermi surface in Ce 2 RhIn 8 is approximately the same as that of La 2 RhIn 8 . The magnetic susceptibility and magnetization of Ce 2 RhIn 8 were analyzed on the basis of the crystalline electric field scheme of localized-4 f energy levels. Pressure-induced superconductivity was confirmed above 1.2 GPa from the resistivity and ac-susceptibility measurements.

We report the first successful growth of a high-quality single crystal by the flux method, and the measurement of its electrical resistivity and magnetoresistance (MR), for the filled skutterudite PrRu4P12, which exhibits a metal–insulator (M–I) transition below TMI 63 K. In zero magnetic field, the resistivity increases from that of the metallic state below 63 K, mirroring the M–I transition, shows a shoulder at around 30 K with a further increase beyond it, and then slowly decreases, showing a faint peak at around 0.6 K. In magnetic fields, the resistivity decreases drastically at low temperatures, i.e., a large negative MR appears, and the peak shifts to higher temperatures, although the field effect is only slight above 7 K.

We present the results of theoretical investigation of the temperature dependence of the extraordinary Hall effect (EHE) in granular metal–metal and metal–insulator alloys in the case of electron–phonon scattering at high temperatures. Skew scattering is assumed to be the dominant mechanism of the EHE. The calculations were carried out using Zhang–Levy model and the effective-medium approximation. The single-site electron–phonon interaction model was considered by analogy to that one in the theory of disordered alloys. In the case of strong spin-dependent scattering there is an additional term in the temperature dependence of the EHE coefficient of magnetic granular alloys in comparison with that for bulk ferromagnets. This term is linear with T 3 . The similar temperature dependence for the EHE conductivity in granular metal–metal and metal–insulator alloys takes place in spite of the different origin of giant magnetoresistance in these systems. The strong temperature dependence of the EHE coefficient can be viewed as an evidence of enhanced spin–orbit interaction at interfaces between granules and the matrix. We show a linear correlation between the interface contribution to the EHE coefficient and the interface contribution to alloy resistivity. The obtained results are in a qualitative agreement with the recent experimental data for nanocomposites.

We report transport measurements on high quality RERu4Sb12 single crystals under magnetic fields up to 14 T and temperatures down to 0.3 K. CeRu4Sb12 exhibits anomalous features in all the transport properties, compared to those for RE = La, Pr and Nd. The thermoelectric power (TEP) shows a huge positive peak over 100 μ V K−1 near 90 K. The Hall coefficient, ~2.0 × 10−9m3 C−1 at room temperature, exhibits a drastic increase below ~100 K to RH ≈ 5.2× 10−8m3 C−1 at 0.3 K. At low temperatures below ~3 K, the TEP exhibits an apparent anomaly correlated with the non-Fermi-liquid behaviour reported in the resistivity and specific heat. We have succeeded in observing Shubnikov–de Haas oscillations both in the magnetoresistance and Hall effect. This result along with the Hall effect suggests small semimetallic Fermi surfaces with highly correlated electrons at low temperatures in contrast with the large FS for LaRu4Sb12. NdRu4Sb12 exhibits anomalies suggesting a ferromagnetic ground state at around 1.4 K above which the resistivity exhibits a negative temperature coefficient up to 6 K.

We have investigated the magnetic characteristics of monatomic scale epitaxial multilayers Fe x /Au 2− x utilizing the electrical and Hall resistivity measurements. The results indicate the existence of two distinct conduction electron scattering centers, one with ferromagnetic perpendicular anisotropy and the other with paramagnetic (or superparamagnetic) character. For x =0.5, the anomalous Hall contribution associated with the former is found to show a temperature-driven sign change at low temperatures. Possible two-dimensional Fe cluster formation is discussed in relation with the two scattering centers.

カーボンブラック (CB) 充てんポリプロピレン (PP) /ポリエチレン (HDPE) ポリマーブレンドの電気抵抗率に及ぼすCB粒子の局在化の影響について検討した. まず, CB粒子をPPと混合した. 引続きCB/PP複合材料とHDPEとを混合して, 逐次混練複合材料を作製した. 最初PP相中に分散していたCB粒子は, 逐次混練試料中ではPP相からHDPE相へ移動しようとする. その結果, CB粒子はPP/HDPE界面に局在化する. PP相およびHDPE相がともに連続相であるとき, PP/HDPE界面に局在化したCB粒子はブレンド中で導電性ネットワークを形成することが期待される. 逐次混練試料は同時混練試料よりも低い常温電気抵抗率および高いPTC (Positive Temperature Coefficient) 強度を示した. これらの結果は, PP/HDPE界面に局在化したCB粒子は導電性に効果的であること, および界面に形成された導電性ネットワークはマトリックス高分子の熱膨張とともに膨張しやすいことを示唆している. CB粒子の局在化を透過型電子顕微鏡 (TEM) 観察により確認した.

The Hall effect and thermoelectric power have been investigated in Co/Cu(Mn) multilayers where the temperature dependent switching between antiferromagnetic and ferromagnetic coupling across a critical temperature ( T b ) is observed. The field dependence of extraordinary Hall resistivity and thermoelectric power follows the scaling relations reported for ordinary GMR systems, suggesting that the characteristics of the conduction electron scattering responsible for the GMR in Co/Cu(Mn) multilayers below T b are basically the same as those in the ordinary GMR systems.

Single crystals of PrTa2Al20 have been investigated by means of single-crystal structural analysis and measurements of magnetization, specific heat, and electrical resistivity. The crystalline-electric-field level scheme of the Pr ions has a nonmagnetic Γ3 doublet ground state and a Γ5 magnetic excited state with an energy separation of 53 K. The 4f-electron contribution to the electrical resistivity shows −log T magnetic Kondo scattering above 50 K and a downward curvature characteristic of a quadrupolar Kondo lattice formation below 20 K. A phase transition appears at 0.65 K in zero field and shifts to higher temperatures in applied fields, indicating that this transition is antiferroquadrupolar (AFQ) in nature. The largely enhanced Sommerfeld coefficient ∼1.5 J/(mol K2) in the AFQ state may indicate the formation of heavy quasiparticles. The hierarchically arranged sequence of the magnetic Kondo regime, quadrupolar Kondo lattice regime, and AFQ ordered state in the wide temperature range 0.2–300 K demo...

We have investigated the resistivity $(\ensuremath{\rho}),$ thermoelectric power (TEP), and Hall coefficient ${(R}_{H})$ on high-quality single crystals of $R{\mathrm{Fe}}_{4}{\mathrm{P}}_{12}.$ TEP in ${\mathrm{CeFe}}_{4}{\mathrm{P}}_{12}$ is extremely large $(\ensuremath{\sim}0.5$ mV/K at 290 K) with a peak of $\ensuremath{\sim}0.75$ mV/K at around 65 K. The Hall mobility also shows a peak at $\ensuremath{\sim}65$ K, suggesting carriers with heavy masses developed at lower temperatures related to the f-hybridized band. Both Pr and Nd systems exhibit an apparent increase of $\ensuremath{\rho}$ with decreasing temperature far above their magnetic transition temperatures. In the same temperature ranges, TEP exhibits unusually large absolute values of $\ensuremath{-}50 \ensuremath{\mu}\mathrm{V}/\mathrm{K}$ for ${\mathrm{PrFe}}_{4}{\mathrm{P}}_{12}$ and $\ensuremath{-}15 \ensuremath{\mu}\mathrm{V}/\mathrm{K}$ for ${\mathrm{NdFe}}_{4}{\mathrm{P}}_{12},$ respectively. For ${\mathrm{PrFe}}_{4}{\mathrm{P}}_{12},$ such anomalous transport properties suggest an unusual ground state, possibly related to the quadrupolar Kondo effect.

Magnetoresistance (MR), Hall resistivity, and thermoelectric power in UCoAl, which exhibits a metamagnetic transition (MT) at low temperatures, have been investigated. Across MT, the MR shows a steplike decrease and increase for the transverse and longitudinal geometries, respectively. The temperature dependence of MR indicates that the magnetic scattering due to the spin fluctuations largely contributes to the electrical resistivity around 17 K. The Hall coefficient and the thermoelectric power show drastic changes associated with MT. Both in the low- and high-field states, the extraordinary Hall effect dominates in the temperature dependence of Hall coefficient. The temperature dependence of thermoelectric power can be qualitatively explained by an extended $s\ensuremath{-}d$ model considering the $5f$ band structure.

Electrical resistivity and calorimetric measurements on Dy 3 Coshow that below the Neel temperature (TN=44 K) the non-collinear antiferromagnetic structure exhibits field-induced magnetic phase transitions of a first-order type along all principal axes, accompanied by a strongly anisotropic giant magnetoresistance and by a change of the Sommerfeld coefficient of the specific heat. Quantum tunnelling of the magnetization appears to be possible for T < 0.6 K.

We have simultaneously measured the field dependence of transverse voltages at two pairs of transverse probes along with the magnetoresistance to detect the motion of ferromagnetic domain walls in a thin NiFe wire. We observed sharp steplike changes of the transverse voltage correlated with the jumps in magnetoresistance, which have been reported previously in thin ferromagnetic wires. The field dependence is explained in terms of the rotation of local magnetization near the transverse probes. This fact suggests that such a local magnetization rotation might contribute to some of the negative domain-wall resistivity reported in recent papers.

We have succeeded in growing Pr x Os 4 Sb 12 single crystals under ~ 4 GPa with high Pr-site filling fraction x. The electrical resistance measurements clearly show that the superconducting (SC) transition is sharper and the onset temperatures is lower in the single crystal samples grown under high pressure compared to that of the sample grown under ambient pressure. These results suggest that the double SC transition ascribed to sample inhomogeneity is suppressed in the sample grown under high pressure. The change of 4f-electron crystalline electric field energy splitting between the Γ 1 ground state and the Γ 4 ( 2 ) first excited state in the sample made under high pressure is proposed as one of the possible origins of the suppression of the double SC transition.

We have investigated high field magnetization on single-crystalline CeFe 2 Ge 2 which is classified as a heavy fermion with a non-magnetic ground state. A clear metamagnetic anomaly, which resembles those reported in CeRu 2 Si 2 , was observed around 300 kOe for the field along the c -axis. The T 3/2 dependence of the electrical resistivity in a wide temperature range from around 15 K down to 2 K, followed by T 2 dependence at lower temperatures, is apparently similar to that in CeNi 2 Ge 2 which is close to a quantum critical point.

We have investigated the thermoelectric power ( S ), Hall coefficient ( R H ), and magnetoresistance (MR) of Pr x Fe 4 Sb 12 ( x ∼ 1 ) synthesized under high pressure. The dependence of S and R H on the Pr-site filling fraction x become apparent at low temperatures. In MR, we confirmed that the electrical resistivity is enhanced by the 4f-electron crystalline electric field effect below ∼ 10 K and suppressed by the 3d-electron spin fluctuation effect above ∼ 10 K . The change of magnetic state in Pr x Fe 4 Sb 12 with x , realized as a combined effect of 4f-electrons and the high electronic density of state at Fermi level, is well reflected in the transport properties.

We have succeeded in synthesizing new filled skutterudite SmFe 4 As 12 under high pressure. We found that SmFe 4 As 12 can be synthesized only in a narrow temperature range near 1170 K. The electrical resistivity shows metallic temperature dependence with the residual resistivity ratio is 20, indicating the reasonably high crystallinity of the sample. The magnetization and the specific heat measurements revealed that SmFe 4 As 12 undergoes a ferromagnetic transition at T C = 39 K .

We have synthesized the filled skutterudite Sm x Fe 4 Sb 12 under high pressure to improve the Sm-site filling fraction x. From the magnetic susceptibility, electrical resistivity and specific heat measurements, we confirmed a ferromagnetic transition at T C ∼ 43 K . We found no drastic change in the magnetic properties caused by the reduced number of the Sm-site vacancy, in contrast with the significant change of the magnetic ground state in Pr x Fe 4 Sb 12 ; from ferromagnetic to non-magnetic one. Such a different response of the magnetic properties to the change in rare earth site vacancy is discussed.

Substitution effect has been studied for the transition metal site on both of the metal–insulator transition in PrRu 4 P 12 and the anomalous nonmagnetic transition (probably of multipolar origin) in PrFe 4 P 12 by mutual alloying. It has been found that both of the transitions are significantly suppressed by the substitution. This observation supports the scenario that the expected Fermi-surface-nesting instability is an essential ingredient for both of the orderings. In the nonordered state, logarithmic temperature dependence in the electrical resistivity indicative of Kondo-like scatterings has been found only around the high Fe concentration, suggesting important roles of the Fe 3d electrons for the strongly correlated behavior.

We have measured the thermoelectric power and Hall effect on three Co–Al–O granular films whose conduction mechanism varies from metallic to tunneling type depending on O content. We obtained a finite thermoelectric power (TEP) which decreases with increasing resistivity. In the tunneling type sample, a large field dependence of TEP correlated with the magnetoresistance has been observed. The Hall coefficient of Co–Al–O decreases with increasing sample resistivity, in contrast with the giant Hall effect reported for Ni–SiO 2 granular sample with a similar resistivity. The dominant electronic conduction mechanisms are found to be different between the giant magnetoresistance and the giant Hall effect in ferromagnetic-metal-oxide granular systems.

Electrical resistivity of CePtSi2 (TN=1. 7 K), CePtGa (TN=3. 5 K) and Y1-x UxPd3 (x=0. 198) have been measured at high pressure. It is found that the antiferromagnetic ordering of the two Ce compounds is suppressed by pressure, i. e., Neel temperature TN becomes zero at a critical pressure Pc to show a non fermi liquid behavior above Pc. By pressurizing more above Pc, the electronic states show a crossover from non Fermi liquid (NFL) to Fermi liquid (FL) states or Kondo state. On the other hand for U-compound which shows NFL properties at ambient pressure a crossover from NFL to FL is also observed by applying pressure. These facts indicate that the NFL state becomes unstable at high pressure. The electronic states of these compounds show a general trends of magnetic ordering → NFL → FL as pressure increases.

The filled skutterudite PrFe4P12 undergoes an antiferro-quadrupolar (AFQ) ordering below T Q = 6.5 K . In a recent resistivity measurement under high pressures, it was reported that T Q is suppressed with applied pressure and an insulating phase appears above 2.4 GPa. To obtain microscopic information about the AFQ phase and the insulating state under pressure, we performed X-ray diffraction experiments. We have succeeded in observing superlattice reflections at the wave vector q = ( 1 , 0 , 0 ) with the intensity being ∼ 10 - 4 of the fundamental Bragg's ones. At 1.4 GPa, T Q is suppressed to 5.5 K, while it is found out that the calculated Fe-ion displacement is almost the same as that at ambient pressure. In the insulating state, on the other hand no superlattice reflections at q = ( 1 , 0 , 0 ) are observed within the experimental error.

We have investigated the field dependence of extraordinary Hall coefficient R s and resistivity ρ in FeAg granular alloys. We found a deviation from the linear scaling relation between R s ( H )/ ρ ( H ) and ρ ( H ) in agreement with the results reported for Co-based granular alloys, suggesting that the deviation from the linear scaling relation is common to granular systems.

The electrical resistivity of Y 1− x Y x Pd 3 ( x = 0.198), which is well known to exhibit non-Fermi-liquid (NFL) behaviors, has been measured under hydrostatic pressure up to 5.8 GPa in order to investigate the stability of NFL state at high pressure. It is found that the coefficient of T -linear term in the ϱ ( T ) curves at low temperatures decreases with increasing pressure and at 5.8 GPa, the T 2 -term characteristic of the normal Fermi liquid is apparently observed below 15 K. On the basis of the present data, the Gruneisen parameter of T K is estimated to be about 10. The electronic structure of NFL at high pressure is briefly discussed.

We find extraordinary superconducting characteristics in the low-temperature specific heat of high quality ${\mathrm{CeCo}}_{2}$ single crystals, suggesting that the superconducting gap is highly anisotropic. The electronic specific-heat jump at the superconducting transition temperature (${\mathrm{T}}_{\mathrm{c}}$ =1.5 K) is \ensuremath{\Delta}${\mathrm{C}}_{\mathrm{e}}$ /\ensuremath{\gamma}${\mathrm{T}}_{\mathrm{c}}$ =0.85, which is reduced compared to the BCS value of 1.43. At low temperatures (0.13/${\mathrm{T}}_{\mathrm{c}}$ \ensuremath{\ll}1), ${\mathrm{C}}_{\mathrm{e}}$ varies approximately as ${\mathrm{T}}^{2}$ , indicating a possibility of lines of nodes in the gap. A possible correlation of the gap anisotropy with the ferromagnetic spin fluctuation is discussed.

We have measured the electrical resistivity, Hall effect and transverse even voltage in the flux-flow state of CeRu2, CeCo2 and Yb3Rh4Sn13. In all the transport properties, we found a clear anomaly related with the peak effect, which was argued in relation to the inhomogenous superconducting phase proposed by Fulde-Ferrell and Larkin-Ovchinnikov. The pinning force and the transverse even voltage depend largely on sample quality. A deviation from the ordinary BCS prediction, suggesting an anisotropy in the superconducting gap, has been found in the specific head of CeCo2/

We have measured the temperature dependence of the electrical resistivity, Hall coefficient, thermoelectric power, magnetic susceptibility and specific heat of CeOs 2 in the two different 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 Ce 4+ valence, while the C15 exhibits various features characteristic of valence fluctuating compounds. This fact explains why only the C14 becomes superconductive.

We have measured temperature dependence of magnetic susceptibility, resistivity, Hall coefficient, and lattice constant of Ce 3 Ir 4 Sn 13 in order to clarify the origin of anomalies at 0.6 and 2 K in specific heat. The susceptibility measurement indicates that the anomaly at 0.6 K is due to an antiferromagnetic ordering. The Hall coefficient, resistivity, and lattice constant exhibit a sharp change at 2 K, indicating that the transition at 2 K involves a change of the band structure accompanied by a lattice expansion below the transition temperature.

We have fabricated Ce/Ta multilayers under ultrahigh vacuum to investigate the magnetic state of Ce in thin layers. The magnetization, electrical resistivity, and Hall effect have been measured for Ce layer thicknesses between 5 and 100 \AA{}. Results of x-ray analysis indicate that Ce atoms crystallize as bulk Ce for ${\mathit{d}}_{\mathrm{Ce}}$=100 \AA{}, and are amorphous for ${\mathit{d}}_{\mathrm{Ce}}$\ensuremath{\leqslant}15 \AA{}. For ${\mathit{d}}_{\mathrm{Ce}}$=100 \AA{}, the Ce \ensuremath{\gamma}-\ensuremath{\alpha} transition observed in the resistivity and reduced magnetization at 2 K suggest the stabilization of \ensuremath{\alpha}-phase Ce at low temperatures. For ${\mathit{d}}_{\mathrm{Ce}}$\ensuremath{\leqslant}15 \AA{}, in contrast, the magnetic susceptibility and extraordinary Hall effect indicate the existence of magnetic Ce down to 1 K. We speculate that the transition to the nonmagnetic state of Ce at low temperatures for ${\mathit{d}}_{\mathrm{Ce}}$\ensuremath{\leqslant}15 \AA{} is prevented by the amorphous structure. \textcopyright{} 1996 The American Physical Society.

The magnetoresistivity and Hall resistivity of Pd/Co multilayers have been investigated down to 4.2 K, focusing on the difference between samples with in-plane and perpendicular magnetization. At 4.2 K, a sign change of the extraordinary Hall coefficient as a function of Co thickness is observed at ∼ 2 A . For a Co layer thickness of 2 A, an anomaly is found in the temperature dependence of both resistivity and Hall coefficient near 250 K, suggesting a magnetic phase transition in an alloyed interface region.