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The cubic compound YbCo2Zn20 has huge electronic specific heat coefficient γ=7900 mJ/molK2 and its ground state could be located in the vicinity of the quantum critical point. To investigate magnetic ground state, we have carried out muon spin relaxation measurements and confirmed non-magnetic ground state with fluctuating tiny magnetic moment.

The crystal structures of two novel ternary compounds, Ce3Pt4Sn6 and Ce1−xPt6Al13+2x (x = 0.207), have been derived by direct methods from X-ray single crystal data. Whereas Ce1−xPt6Al13+2x is of a new structure type (a = 1.42224(2) nm, c = 0.87367(1) nm, space group P 6 ¯ 2 m ), Ce3Pt4Sn6 was found to crystallize in two different crystal modifications, (i) a monoclinic variant (a = 0.93682(2) nm, b = 0.46145(1) nm, c = 1.40434(3) nm, β = 99.635(1)°, space group P21/m), which is isotypic with the Y3Pt4Ge6-type and (ii) an orthorhombic modification (a = 2.76394(4) nm, b = 0.460588(7) nm, c = 0.93530(1) nm, space group Pnma), which crystallizes with the ordered Pr3Pt4Ge6-type. For the monoclinic arrangement m-Ce3Pt4Sn6 an intrinsically defect growth pattern was found – it grows in two related motifs (opposite directions of pentagonal units) in the ratio of 90% : 10% ensuring a stoichiometric composition. TEM observation directly revealed intrinsic building defects detected by single crystal X-ray diffraction for m-Ce3Pt4Sn6. Diffuse streaks in electron diffraction and inhomogeneous contrasts in a high resolution TEM image indicate the existence of a random stacking sequence between two related motifs.

The Laves phase compound CePt 2 crystallizing in the cubic C15 (MgCu 2 type) structure orders antiferromagnetically at 1.8 K. Single crystalline samples of Ce 1− x Pb x Pt 2 (0 x . 5) have been prepared by the self-flux method. It is found that Pb atoms replace preferentially the Ce atoms in the face-center-cubic sublattice, forming a superlattice structure of the cubic C15b (MgSnCu 4 type). We have measured the specific heat, magnetic susceptibility, and electrical resistivity. The results reveal that the Ce valence remains trivalent in Ce 1− x Pb x Pt 2 ( x ⩽ 0.43) but the superlattice formation suppresses the antiferromagnetic ordering temperature below 0.35 K for x = 0.43.

To match the excellent performance of n-type type-VIII clathrate Ba8Ga16Sn30 single crystals in thermoelectric (TE) generator design, synthesizing a large size p-type counterpart with a high TE figure of merit ZT continues to be a challenge for many years. In this work, we obtained 7-mm-diameter single crystals of Zn-substituted type-VIII clathrate Ba8Ga16Sn30 (Zn-BGS) with various carrier concentrations by Ga-flux method. Though the actual substituted compositions of the single crystals Ba8Ga15.9ZnySn30.1 (y = 0–0.019) are much lower than the nominal ones, the Zn atoms work as a “spur” and effectively suppress the nucleation rate of BGS in the Ga-flux, which is vital to achieving a similar large size crystal with the n-type counterpart. The y = 0.006 and 0.007 crystals share nearly the same or a slightly lower value of resistivity with a pristine crystal in the whole temperature. However, the Hall coefficient measurement revealed that Zn substitution triggers a profound transition from a “low-carrier-con...

Single crystals of Ce3Pt4Sn6 (I) and Ce1-xPt6Al13+2x (x = 0.207, (II)) are isolated by mechanical fragmentation of specimens grown from self-fluxes (Sn or Al, resp.) by slow cooling from the melt.

Type-I clathrate Ba8Ga16Sn30 is known as a typical example showing glass-like behavior in the thermal conductivity at low temperatures. We report on thermoelectric properties above room temperature for the p- and n-type single crystals which were grown from Ga–Sn double flux and Sn single flux, respectively. The measurements of electrical resistivity showed hysteretic behaviors when the sample was heated to 600 K. Powder X-ray diffraction analysis indicated that the type-I structure changed to the type-VIII after the sample was heated to 600 K. By using the data of Seebeck coefficient, electrical resistivity, and thermal conductivity, we estimated the dimensionless figure of merit ZT for the type-I Ba8Ga16Sn30. For the p- and n-type samples, the values of ZT reach 0.58 and 0.50 at around 450 K, respectively, which values are approximately half of those for the type-VIII counterparts.

The intermetallic clathrate Ba8Ga16Sn30 (BGS) is dimorphic, possessing α-phase (type-VIII) and β-phase (type-I). To determine the stability ranges of the two phases, we performed a study of the phase diagram by combining differential thermal analysis (DTA) and power X-ray diffraction (XRD) on both samples of bulk single crystals (≅1 mm) and powdered crystals (

Single-crystal samples of the type VIII clathrate Ba8Ga16−xAlxSn30 (0 ≤ x ≤ 12) were prepared by the Sn-flux method, and the structural and electrical properties were studied from 300 K to 600 K. The lattice parameter increases linearly as x is increased from 0 to 10.5, which is the solubility limit of Al. For all samples, the electrical conductivity σ decreases monotonically as the temperature is increased. σ(T = 300 K) increases from 1.88 × 104 S/m for x = 0 to 3.03 × 104 S/m for x = 2, and then gradually decreases to 2.4 × 104 S/m with further increase of x to 8. The increase of σ for Al-substituted samples is attributed to enhancement of carrier mobility. The Seebeck coefficients of samples with 0 ≤ x ≤ 8 are negative with large values, and the absolute values increase from 240 μV/K to 320 μV/K as the temperature increases from 300 K to 600 K. At 300 K, the effective mass m*/m0 is in the range from 0.53 to 0.67, and the samples with x = 6 and x = 8 have a rather low thermal conductivity of 0.72 W/mK and 0.78 W/mK, respectively. ZT reaches 1.2 at 500 K for x = 6.

T. Mitoa,∗, T. Koyama, K. Nakagawara, T. Ishida, K. Ueda, T. Kohara, K. Matsubayashi, Y. Saigab,†, K. Munakata, Y. Uwatoko, M. Mizumaki and N. Kawamura Graduate School of Material Science, University of Hyogo, Hyogo 678-1297, Japan Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan Japan Synchrotron Radiation Research Institute, SPring-8, Sayo, Hyogo 679-5198, Japan

Ultrasonic measurements have been carried out on the heavy-fermion compound ${\text{YbCo}}_{2}{\text{Zn}}_{20}$ to investigate the elastic properties and the $4f$ electric state of Yb ion. A strong temperature dependence at low temperature was found in elastic constants ${C}_{11}$, $({C}_{11}\ensuremath{-}{C}_{12})/2$, and ${C}_{44}$ of ${\text{YbCo}}_{2}{\text{Zn}}_{20}$. Furthermore, the elastic constants are significantly magnetic field dependent at low temperatures. These experimental facts strongly suggest an importance of the highly degenerated $4f$ low-lying level scheme of Yb ions under a crystalline electric field effect, probably leading to such an extremely large Sommerfeld coefficient of ${\text{YbCo}}_{2}{\text{Zn}}_{20}$. We argue that the near spherical distribution of neighboring Zn atoms centered at the Yb site is an essential requirement for the formation of such an exotic heavy-fermion system.

We report on the magnetic, transport, and thermal properties of a cage-like compound CeFe 2 Al 10 that crystallizes in the orthorhombic YbFe 2 Al 10 -type structure. A broad peak in the magnetic susceptibility at 70 K indicates that CeFe 2 Al 10 is a valence fluctuation compound. The electrical resistivity and the Hall coefficient exhibit sharp upturns below 20 K, where the thermopower shows a rapid decrease. These low-temperature anomalies in the transport properties resemble those of a typical Kondo semiconductor CeRhSb. These features indicate the formation of a hybridization gap in CeFe 2 Al 10 on cooling below 20 K. The energy gap is estimated as 15 K from the thermal activation energy of the resistivity. The magnetic contribution of the specific heat shows a Schottky-type maximum at 30 K that provides another evidence for the gap formation in CeFe 2 Al 10 .

YbInCu4 undergoes a first‐order isostructural valence transition at TV = 42 K, which is accompanied by a 0.5% volume increase due to cooling. In order to elucidate the valence transition, both the linear thermal expansion and magnetostriction, ΔL/L, of a YbInCu4 single crystal were measured using strain gauges under high pressures of up to 3.0 GPa and a magnetic field of up to 18 T. The abrupt volume change during the valence transition was confirmed to decrease linearly with TV under a high pressure. It was also observed that TV was suppressed upon application of a magnetic field. On the basis of the results, we have established a T‐P‐B phase diagram for the first‐order valence transition in YbInCu4.

Electrical resistivities of YbMn 2 Ge 2 were measured at several pressures in a temperature range from 2 K to room temperature. In low temperature region below 100 K, temperature dependence of the resistivity shows significant change between 2.0 and 4.0 GPa. Under 4.0 GPa, anomalies of the resistivity were observed at ( T t 3 ∼ ) 21.6 K and ( T t 4 ∼ ) 7.1 K. There is a fair possible that they originated from novel magnetic phase transitions of Yb or Mn sublattice. With increasing pressure, T t 4 increases linearly. In contrast to the pressure dependence of T t 4 , T t 3 decreases linearly.

We report the electrical resistivity and specific heat of the intermediate-valence intermetallic compound YbAl 2 . A single-crystalline YbAl 2 was synthesized by the Li-flux-growth technique. Electrical resistivity measurements were performed under high pressures up to 2.3 GPa. The value of the electrical resistivity increases with increasing pressure. This behavior is attributed to the gradual increase of the Yb valence in YbAl 2 .

Thermal neutron elastic scattering experiments revealed that iron localized moments form in an antiferromagentic short range ordering in LuFe 2 Ge 2 below 9 K. A long range type antiferromagnetic ordering grows rapidly under high pressure above 1.6 GPa.

EuSnP shows an antiferromagnetism below T N = 21 K , in which two metamagnetic transitions were observed with applying magnetic field along both the directions parallel and perpendicular to the c -axis of tetragonal structure. In addition, entropy released up to T N was only ∼ 75 % of R ln 8 which is the value of entropy expected from Eu2+ state. These might bring about novel antiferromagnetic ground state with noncollinear configuration of Eu2+ moments.

The low-temperature properties of YbCo2Zn20, which shows a giant specific heat at low temperatures, have been studied by the 59Co-nuclear quadrupole resonance (NQR) technique. The measurement of sp...

Type-VIII clathrate Ba8Ga16Sn30 is a promising thermoelectric material in the 400?600?K range. We report on the effects of Ge substitution for Sn on both crystal growth and thermoelectric properties. In a series of samples prepared from the initial composition of Ba8 Ga40 Sn30?X GeX (0???X???6), the size of single crystals reaches the maximum of 8?mm at X?=?0.5. The atomic composition of single crystals is found to be described as Ba8Ga15.9Sn30.1?xGex (0???x???4.73). Ge substitution results in the increase in the positive Seebeck coefficient and electrical resistivity by 1.3 and 2 times at the maximum, respectively, whereas the hole carrier density does not change substantially. Taken together with the thermal conductivity data, the maximum of the dimensionless figure of merit ZT reaches 0.87 at 540?K for x?=?0.07.

We have investigated the field dependences of Yb valence as well as of the magnetic properties of the heavy-fermion (HF) compound YbCo 2 Zn 20 by X-ray absorption spectroscopy, 59 Co nuclear magnet...

We have carried out 59 Co-nuclear magnetic resonance (NMR) measurements on the heavy Fermion compound YbCo 2 Zn 20 , which shows an extremely large specific heat. After examining site symmetry at the Co position by studying a single crystal sample at different directions of magnetic field, we have analyzed powder patterns obtained over a wide range of field from 0.8 to 7.2 T. The temperature dependent component of the Knight shift, which arises from 4 f moments, is largely suppressed with increasing field, resulting in weak temperature dependence at low temperatures. This is a sign of field-induced Fermi liquid states, consistent with previous transport measurements on this compound.

We have grown single-crystalline samples of Zn-substituted type-VIII clathrate Ba8Ga16Sn30 with n-type carriers by Sn-flux method. The actual compositions of the single crystals were found to be described as Ba8Ga15.8-2yZnySn30.2+y (y = 0 ∼ 0.54), where the charge balance is well maintained. As y goes from 0 to 0.42, the resistivity at 300 K decreases from 5.3 to 3.0 mΩ cm gradually, but the effective mass is essentially constant at 1.2 ∼ 1.5m0, indicating intact band structure near the conduction band minima upon Zn substitution for Ga. At elevated temperatures, the ambipolar effect on the thermal conductivity becomes less pronounced upon Zn doping, and the dimensionless figure of merit ZT for y = 0.07 and 0.42 remains at rather high values compared with the nondoped sample.

Single crystalline samples of type-VIII clathrate Ba_8Ga_Cu_xSn_ (0 ≤x ≤ 0.033) were prepared by the Sn-flux method. Upon substituting Cu for Ga, the carrier mobility at 300 K increases twice while the carrier density stays in the range 3.1-4.2×10^/cm3. Consequently, the electrical resistivity is decreased from 5.3 mΩcm for x=0 to 3.2 mΩcm for x=0.033. Irrespective of x, the Seebeck coefficient is largely negative and linearly changes with temperature in the range 300

We report the dramatic change of gapless semiconductor properties by different chemical doping elements of Co and Mn into PbPdO_2. The metal-insulatorlike transition temperature T_ = 100 K for PbPdO_2 shifts to a higher temperature of 150 K by the Co doping and to a lower temperature of 70 K by the Mn doping. Because of the anisotropic band structure with the majority of heavy holes and the minority of light electrons, the transport and magnetic properties are significantly changed by the chemical doping elements. At low temperatures, the Co doping enhances ferromagnetic interactions, whereas the Mn doping favors antiferromagnetic interactions. These results are of great interests because you can control the magnetic ordering as well as manipulate the carrier density by changing the doping elements. These materials could be a good candidate for spintronics applications.

Single-crystalline samples of type-VIII clathrate Ba8Ga16-xAlxSn30 (0

PbPdO2 is a new class of gapless semiconductors, which is extremely sensitive to external influences such as temperature, magnetic field, and carrier doping, because of their peculiar band structure. With varying temperature, a broad transition from a high-temperature metallic behavior to a low-temperature insulating behavior was observed at TMI=100 K in the electrical resistivity, which is related to the thermally assisted excitation near the Fermi level due to its gapless band structure. By doping 10% Co for Pd in PbPdO2, the number of hole charge carriers was increased by ten times, and the transition temperature was increased to TMI=150 K. When applying a magnetic field, a ferromagnetic component was found at low temperatures in the magnetization curves of both materials, in addition to diamagnetic background signals for PbPdO2 and paramagnetic background signals for PbPd0.9Co0.1O2. In the low temperature regime, the slope of magnetoresistance is negative, while it is changed into positive with a quad...

Electrical resistivity ρ, specific heat C , magnetization M measurements are reported on four compounds, LaRu 2 Zn 20 , PrRu 2 Zn 20 , LaIr 2 Zn 20 , and PrIr 2 Zn 20 , which crystallize in a cubic CeCr 2 Al 20 -type structure. LaRu 2 Zn 20 , LaIr 2 Zn 20 , and PrIr 2 Zn 20 show superconducting transitions at T C = 0.2, 0.6, and ∼0.05 K, respectively, whereas PrRu 2 Zn 20 remains a normal state down to 0.04 K. This is the first observation of superconductivity in the family of RT 2 X 20 (T = transition metal; X = Al and Zn). Furthermore, structural phase transitions manifest themselves at T s = 150, 138, and 200 K for LaRu 2 Zn 20 , PrRu 2 Zn 20 , and LaIr 2 Zn 20 , respectively. No magnetic transition is found in PrRu 2 Zn 20 and PrIr 2 Zn 20 down to 1.8 K. On cooling PrIr 2 Zn 20 below 2 K, the specific heat divided by temperature, C / T , continuously increases and reaches 5 J/(K 2 ·mol) at 0.4 K, suggesting that Pr 4 f 2 electrons are involved in the heavy-fermion state, as observed in a related compo...

We have performed the electrical resistivity measurement on single crystal heavy fermion compounds YbT2Zn20 (T = Co, Rh, Ir) under pressure up to 12 GPa. A pronounced resistivity maximum Tmax, which scales with the Kondo temperature, develops with increasing pressure. In the case of YbCo2Zn20, Tmax initially decreases with increasing pressure, reaches a minimum around 1 GPa, above which the pressure-induced magnetic ordering emerges at low temperature. For YbRh2Zn20 and YbIr2Zn20, Tmax also exhibits a minimum at approximately 3 GPa, suggesting the appearance of pressure-induced magnetic transition below 2 K. Our results indicate the proximity to a magnetic instability in YbT2Zn20 systems at ambient pressure.

We present results of the magnetic susceptibility, electrical resistivity and thermopower for CeT2Al10 (T=Fe and Ru) crystallizing in the orthorhombic YbFe2Al10-type structure. The magnetic susceptibility for CeFe2Al10 shows a maximum at 70 K which is a characteristic of a valence fluctuation system. The electrical resistivity below 20 K exhibits semiconducting behaviour with an energy gap of 15 K. On the other hand, CeRu2Al10 displays Curie-Weiss behaviour of Ce3+ in the susceptibility down to 30 K, and undergoes an antiferromagnetic transition at TN=27 K. The semiconducting behaviour of the resistivity between 70 K and 30 K is described by a gap of 50 K. On cooling below TN, however, the resistivity exhibits a peak at 23 K and falls down. The thermopower shows two maxima at 22 K and 6 K. These findings suggest that the magnetic order induces a semiconductor-to-metal transition in CeRu2Al10.

We report ultrasonic measurements on the high quality single crystal of the Yb-based heavy fermion compound YbRh2Zn20 over a temperature range from 200 K to 0.5 K. A shallow, but clear minimum was observed in the temperature dependent elastic constants C11, (C11 – C12)/2 and C44 around 15 K, probably attributed to the ground state and low-lying excited states of Yb3 in the cubic CEF. We discuss the low-temperature elastic properties and possible energy level scheme of localized 4f state of Yb3 ions in YbRh2Zn20. CEF ground state developed at the low temperatures and physical parameters relating to a quadrupolar moment in YbRh2Zn20

We have studied the electrical resistivity of YbCo2Zn20 under magnetic field up to 18 T. With applying magnetic field, the contribution of the Kondo interaction to the electrical resistivity is suppressed and the Fermi liquid regime is extended to higher temperature range. Both the T2 coefficient of the electrical resistivity A and the residual resistivity ρ0 strongly decrease in magnetic field. From the magnetic variation of the resistivity, it has been found that YbCo2Zn20 is classified as a heavy fermion system with small Kondo temperature of ~ 1.0K.

We have measured the electrical resistivity of a single crystal of YbCo2Zn20 at pressures up to 2.37 GPa and at temperatures from 50 mK to 300 K. Above a critical pressure P. (similar to I GPa), we have found a resistivity anomaly at T-M (similar to 0.15 K at 1 GPa) that increases with the pressure. At the ambient pressure, the system shows a nonmagnetic ground state described by the Fermi-liquid model. The T-2 coefficient of the electrical resistivity A strongly increases with the pressure upon approaching Pc. However, in the vicinity of P,, the temperature dependence of the resistivity deviates from the Fermi-liquid description. These observations suggest that the application of hydrostatic pressure induces a magnetically ordered state for P >= P-c and T