Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Two conflicting ground states, i.e., an antiferromagnetic ground state at 3.8K and aferromagnetic ground state at 5.1 K, have been reported for CePtGe2, which has two nonequivalent crystallographic Ce sites. In this study, we have prepared polycrystalline and single-crystalline CePtGe2 samples and measured their magnetization, specific heat, resistivity, and Seebeck coefficient. The observed bend in resistivity, peak in magnetic susceptibility, and lambda-type anomaly in specific heat at T-N = 3.8K and the metamagnetic transition in this CePtGe2 suggest antiferromagnetism at low temperatures. No evidence of ferromagnetic order was found in the studied temperature range, indicating possible crystal polymorphism with ferromagnetic character. The large susceptibility around TN and the Schottky-type specific heat indicate a well-localized f -electron state. However, the large residual gamma and X(0) indicate an itinerant heavy f -electron state. These findings suggest the coexistence of localized and heavy itinerant states corresponding to f electrons at the two Ce sites in this antiferromagnetic CePtGe2. The field dependence of magnetization indicates a sudden increase in magnetization at weak magnetic fields (similar to 0.2T), followed by a plateau at fields above 0.2 T, resulting in a possible different polarized metamagnetic state via interaction between localized and itinerant f electrons.

DOI： 10.1103/PhysRevB.100.035107

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DOI： 10.11316/jpsgaiyo.74.2.0_1928

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DOI： 10.11316/jpsgaiyo.74.1.0_1978

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We have discovered a new orthorhombic ternary compound SmPtSi2. We succeeded in growing a single crystal of SmPtSi2
prepared a polycrystalline sample of this compound, and measured their susceptibility, specific heat, and resistivity. The temperature dependence of susceptibility of the polycrystalline sample is close to that of Sm3+ at high temperatures, and its specific heat shows anomalies at TH = 8.6 K and TL = 5.6 K. The resistivity of a single crystal of SmPtSi2 shows a hump-type anomaly just below TH and a sudden decrease at TL, indicating that these anomalies are intrinsic and that SmPtSi2 exhibits a two-step transition.

DOI： 10.1016/j.physb.2017.10.028

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DOI： 10.11316/jpsgaiyo.73.2.0_541

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DOI： 10.11316/jpsgaiyo.73.2.0_1568

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DOI： 10.11316/jpsgaiyo.73.2.0_1187

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DOI： 10.11316/jpsgaiyo.73.2.0_1188

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DOI： 10.11316/jpsgaiyo.73.2.0_1518

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DOI： 10.11316/jpsgaiyo.73.2.0_609

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DOI： 10.11316/jpsgaiyo.73.2.0_1714

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In this study, the superconducting gap symmetry of LaO0.5F0.5BiSSe is elucidated through specific heat measurements with one single crystal of LaO0.5F0.5BiSSe. A clear jump is observed at 3.95 K in LaO0.5F0.5BiSSe, suggesting bulk superconductivity. From specific heat measurements, Delta C-e/gamma T-c and 2 Delta(0)/k(B)T(c) are obtained as 2.31 and 4.5. These values indicate strong electron-phonon coupling superconductivity. The temperature (T) and magnetic-field (H) dependence of the electronic specific heat C-e(T, H) suggests that superconductivity is fully gapped. Our handmade system successfully elucidates superconducting gap symmetry of the BiS2-based compound with a small single crystal.

DOI： 10.1103/PhysRevB.96.214506

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DOI： 10.11316/jpsgaiyo.72.1.0_2150

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Superconductivity is discovered in Y6Tr4Al43 (Tr = Nb, Mo, Ta) with a peanut-shaped cage structure at T-c = 0.86, 0.75, and 0.68 K, respectively. The superconducting state is revealed by performing electrical resistivity and specific heat measurements. The upper critical field is obtained to be 0.22 (Nb), 0.175 (Mo), and 0.15 T (Ta). A specific heat jump provides evidence of bulk superconductivity in these compounds.

DOI： 10.7566/JPSJ.85.105001

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DOI： 10.1016/j.phpro.2016.04.025

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DOI： 10.1016/j.phpro.2016.04.024

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DOI： 10.1016/j.phpro.2016.04.023

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Superconductivity was observed in SrPd2Sb2 polymorphs: a primitive tetragonal CaBe2Ge2-type (low-temperature phase, LT-SrPd2Sb2) structure and body-centered ThCr2Si2-type (high-temperature phase, HT-SrPd2Sb2) structure. The superconducting transition was observed at T-c = 1.95 (LT) and 0.6K (HT). The specific heat C(T) showed a clear anomaly at T-c = 1.85 (LT) and 0.6K (HT); thus, the superconductivity was of a bulk nature. The agreement with the Bardeen-Cooper-Schrieffer (BCS) curve indicated that the LT-SrPd2Sb2 superconductor was fully gapped. The values of electron-phonon coupling lambda(ep) and density of state at Fermi level N(E-F) in 122 compounds with the CaBe2Ge2-type and its related structure were evaluated to reveal the main factor that determines T-c. From our systematic analysis, T-c of this family can be explained by lambda(ep) rather than N(E-F).

DOI： 10.7566/JPSJ.85.043701

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We discover a new superconductor, TiIrSi at T-c = 1.4 K, and reveal a superconducting state of TrIrSi (Tr = Ti, Zr, and Hf) by using dc magnetic susceptibility chi(T), electrical resistivity rho(T), and specific heat C(T) measurements. Superconductivity of TrIrSi is confirmed in rho(T) at T-c = 1.4, 1.85, and 3.4 K, respectively. The electronic specific heat C-e(T) of TrIrSi can be fitted with the theoretical BCS curve of the weak-coupling limit with Delta C-e/gamma T-c = 1.43. Measurements in several magnetic fields suggest that TrIrSi is a type-II superconducting material with upper critical fields of mu H-0(c2)(0) = 0.751, 0.618, and 2.23 T, respectively. The electron-phonon coupling constants lambda(ep) are calculated to be 0.441, 0.464, and 0.545, which are consistent with the weak- coupling limit inferred from the specific jump. The T-c of TrIrSi depends on lambda(ep) and is inversely proportional to N(E-F).

DOI： 10.1088/0953-2048/29/3/035011

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DOI： 10.1088/1742-6596/683/1/012034

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DOI： 10.1088/1742-6596/683/1/012021

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DOI： 10.1088/1742-6596/683/1/012019

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DOI： 10.1088/1742-6596/683/1/012027

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We examined the low temperature magnetic properties of a single crystal of TmTi2Al20, a hole analogue of PrTi2Al20, by means of specific heat C(T) and magnetization M(T, H) measurements. At low field, an anomaly that can be ascribed to an antiferromagnetic ordering is observed in M(T) at T-N = 0.7 K. C(T) shows a very sharp lambda-type anomaly at 0.7 K, confirming the phase transition. From the calculated magnetic entropy S(T), we found that the ground state of TmTi2Al20 is likely to be a magnetic Gamma(5) triplet in the J = 6 multiplet.

DOI： 10.1088/1742-6596/592/1/012052

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Complex ac susceptibility, chi = chi' - i chi '', measurements of the clathrate compound Pr3Pd20Ge6 were performed in static fields up to 10 mT for H parallel to [001] and at temperatures down to 500 mu K. Praseodymium (Pr) nuclear magnetic moments at the 8c site, where quadrupole moments of 4f electrons order at T-Q1 = 250 mK, were found to order antiferromagnetically at 9 mK, as shown by a peak in chi' and a substantial increase in thermal relaxation time. The large enhancement factor (1 + K-8c) obtained by calculation of the hyperfine-enhanced nuclear susceptibility of Pr at the 8c site accounts for the high transition temperature of Pr nuclear magnetic moments and the large chi' below 30 mK. From analysis of the crystalline electric field and the mean-field approximation, we conclude that a chi peak at 77 mK can be ascribed to an antiferromagnetic ordering of magnetic moments of 4f electrons at the 4a site. We found that nuclear and f-electron moments order separately on two sublattices in this compound. The temperature and magnetic field dependence of chi' and chi '' between 30 and 60 mK are discussed in terms of dissipation phenomena.

DOI： 10.1103/PhysRevB.90.100402

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We report on the vibrational properties of the lanthanum filled skutterudite compounds LaRu4Sb12, LaOs4Sb 12, and LaOs4As12studied by inelastic neutron scattering. The experimental data are backed up by ab initio lattice dynamics calculations of the complete series of lanthanum filled skutterudites LaT 4X12with T = Fe, Ru, Os and X = As, Sb. We present details of their structural properties, phonon dispersion relations, vibrational densities of states Z(w) and specific heats CV(T) calculated from Z(w) within the harmonic approximation. Powder averaged lattice dynamics (PALD) technique is applied to approximate the experimental signal presented as the generalized density of states G(w) with high accuracy. Furthermore, the PALD approach is exploited to compute average transverse vtPALD and longitudinal v1PALD sound velocities, elastic constants c11 PALD, c44 PALD, bulk moduli B PALD, and Debye temperatures θD ALD. The PALD results are compared with data computed from ab initio lattice dynamics calculations. All calculated properties are in very good agreement with literature data. © 2013 The Physical Society of Japan.

DOI： 10.7566/JPSJ.82.114607

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The Yb-based heavy-fermion compound Yb2Ni12P7 with a hexagonal Zr2Fe12P7-type crystal structure was investigated by using the 31P nuclear magnetic resonance (NMR) technique. The complicated NMR line changes its shape gradually with decreasing temperature, implying the presence of some Knight shift components. The temperature dependences of the Knight shift and the nuclear spin-lattice relaxation rate 1/T 1 suggest the delocalization of 4f electrons. © 2013 The Korean Physical Society.

DOI： 10.3938/jkps.63.416

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The low-temperature magnetic properties of RE2Ni 21B6 (RE = Er, Tm, Yb and Lu) crystallizing into a cubic C6Cr23-type structure were investigated by measuring magnetic susceptibility, electrical resistivity and specific heat. An off-stoichiometric Er compound with a single phase undergoes antiferromagnetic ordering at 0.61 K. Tm and Yb compounds have no magnetic ordering down to 50 mK. The 4f-electron ground state under a cubic crystalline electric field was deduced by the analysis of the specific heat for each magnetic compound. Tm 2Ni21B6 is considered to have the non-Kramers T3-doublet ground state with a quadrupolar moment. The quadrupolar moment does not show a long-range order, but probably enters into a glass state owing to the presence of atomic disorder. Our study suggests that atomic disorder degrades the long-range nature of quadrupolar interactions. © 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2013.01.073

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We present results of specific heat measurements on a Ce3Pd20Si6 single crystal and construct the magnetic phase diagram for the three cubic principal directions [100], [110] and [111]. The highly anisotropic phase diagram is discussed and can be qualitatively explained by the Zeeman splitting at the 8c-site. For B parallel to [100], the present study found two different quadrupolar ordered phases, which meet the paramagnetic phase at a tri-critical point and establish the new phase boundaries.

DOI： 10.1088/0953-8984/25/12/126003

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DOI： 10.1088/1742-6596/391/1/012071

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We prepared single-crystal samples of hexagonal R2Ni12P7 (R = Sm, Gd-Lu) using a Sn-flux method, and measured their magnetization, resistivity, and specific heat. The antiferromagnetic order in Gd2Ni12P7 and Ho2Ni12P7, the ferromagnetic order in Dy2Ni12P7 and Er2Ni12P7, and the ferromagnetic-like order in Sm2Ni12P7, Tb2Ni12P7, and Tm2Ni12P7 were evidenced by the results of the measurements. In contrast, we found that Yb2Ni12P7 is in a heavy fermion state at low-temperature region. Hump-type anomalies in specific heat were observed below the magnetic transition temperature in R2Ni12P7 (R = Gd, Tb, and Dy), indicating the Zeeman splitting of the J-multiplet of the R3+ ion in the ordered state.

DOI： 10.1143/JPSJ.81.074601

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DOI： 10.1143/JPSJ.81.034710

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We prepared single crystals of Yb2Ni12P7 using a Sn-flux method and measured their resistivity under hydrostatic pressure up to 8 GPa. At ambient pressure, the magnetic part of resistivity rho(mag)(T) shows a peak around T-max similar to 100 K and T-2 dependence below the characteristic temperature of the Fermi liquid, T-FL = 3 K. When pressure increases up to 2.06 GPa, the value of rho(mag)(T) above T-max decreases slightly but rho(mag) below T-max increases slightly. TFL decreases with increasing pressure, and is expected to become zero at 2.5 GPa. Around this pressure, the coefficient of T-2 in rho(mag) significantly increases, suggesting the existence of a quantum critical point. Above 2.5 GPa, overall rho(mag) gradually decreases with increasing pressure up to 6 GPa, but it below 15.5 K increases above 6 GPa.

DOI： 10.1088/1742-6596/391/1/012052

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We report the specific heat measurement of single crystalline Ce3Pd20Si6 and the resultant magnetic phase diagram for the direction of B//[100]. In zero field, we confirmed two successive phase transitions at T = 0.24 K and 0.4 K. The magnetic phase diagram clearly shows a phase boundary of paramagnetic phase I, quadrupole ordered phase II and II'.

DOI： 10.1088/1742-6596/391/1/012054

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We succeeded to prepare large single crystals. We present the electrical resistivity, the magnetic susceptibility and the low-temperature specific heat measurements of unfilled skutterudite NiP3. The temperature dependence of the electrical resistivity of NiP3 is metallic and the residual resistivity ratio, RRR, is estimated to be about 30. No superconductivity was found down to 0.078 K. The magnetic susceptibility shows weakly temperature dependent Pauli paramagnetism. The electronic specific-heat coefficient was determined to be 8.0 mJ/mole·K2. © 2011 The Physical Society of Japan.

DOI： 10.1143/JPSJS.80SA.SA035

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We have synthesized RR'S3(R=La, Ce, Pr, Nd
R'=Yb, Lu) by a flux method, with a flux of potassium iodide, KI, and have measured the magnetic susceptibility and specific heat. The magnetic susceptibility of LaYbS3, CeYbS3, CeLuS3, PrLuS3 and NdLuS3 follows a Curie-Weiss law at high temperatures. From the slope of χ-1 versus T, we evaluate the valence of all rare-earth elements to be trivalent. LaYbS3, CeYbS3, CeLuS3, and PrLuS3 show no clear magnetic transition, while NdLuS3 shows one at 0.25 K. © 2011 The Physical Society of Japan.

DOI： 10.1143/JPSJS.80SA.SA079

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We present the magnetic susceptibility and low-temperature specific-heat of Ho2Ni12P7. The magnetic susceptibility of Ho2Ni12P7 follows a Curie-Weiss law down to 10 K. Ho2Ni12P7 orders antiferromagnetically below Néel temperature TN = 10 K. The magnetization exhibits a metamagnetic behavior below TN. The specific-heat shows a clear peak due to the transition. The crystalline-field ground state of Ho2Ni12P7 is a doublet. © 2011 The Physical Society of Japan.

DOI： 10.1143/JPSJS.80SA.SA081

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We have carried out 121,123Sb nuclear quadrupole resonance (NQR) measurements on ReRu4Sb12 (Re = La, Ce and Pr) to investigate an anomalous behavior of the nuclear spin-echo relaxation rate 1/T2 observed in ReOs4Sb12. The full width at half maximum of the NQR spectrum shows a step-like increase below 130 K with decreasing temperature. Temperature dependence of 1/T2 also shows a divergence at ∼115 K whereas the nuclear spin-lattice relaxation rate 1/T1 does not show any anomaly. These results are caused by a distribution of the electric field gradient (EFG) and its fluctuations, which might arise from a rattling motion of the rare earth ion centered in the cage which consists of twelve Sb and/or a small deformation of the cage. The EFG fluctuations observed in ReOs4Sb12 and ReRu 4Sb12 at T ∼ 120 K originates from an unique crystal structure of the filled skutterudite with oversized Sb-cage. © 2011 The Physical Society of Japan.

DOI： 10.1143/JPSJS.80SA.SA027

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DOI： 10.1143/JPSJS.80SA.SA058

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We have studied quadrupole ordering and rattling in clathrate compound Pr3Pd20Ge6 using ultrasonic measurements. The softening were observed in temperature dependence of elastic constants C-11, (C-11 - C-12)/2 and C-44. The C-11 and (C-11 - C-12)/2 show minimums at 250 mK indicating a transition point to an antiferroquadrupole ordered phase due to a F3 doublet ground state at 8c site. Furthermore, the C-11, (C-11 - C-12)/2 and C-44 exhibit discontinuitive anomalies at 60 mK revealing a ferroquadrupole ordering due to a F-5 triplet ground state at 4a site. Two distinctive ultrasonic dispersions caused by thermally activated F-5-type rattling were observed in C-44 around 15 K and 25 K.

DOI： 10.1088/1742-6596/273/1/012002

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In order to investigate ordered phases revealed at low temperatures in clathrate compound Pr3Pd20Si6, we have performed ultrasonic measurements using a single crystal in magnetic fields at low temperatures. Temperature dependence of elastic constant C-11 and C-L[1 (1) over bar0] = (C-11 + C-12 + C-2(44))/2 shows the anomalies at about 150 mK in zero field. Magnetic phase diagrams are determined by measuring C-11 in H parallel to [001] and C-L[1 (1) over bar0] in H parallel to [111]. The magnetic phase diagrams along the three principal axes indicate a closed loop and a strong magnetic anisotropy. This result suggests that antiferroquadrupole ordering appears at low temperatures in Pr3Pd20Si6.

DOI： 10.1088/1742-6596/200/1/012121

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Ultrasonic measurements on a Pr0.55Nd0.45Os4Sb12 single crystal for temperature down to 20mK and frequencies up to 245 MHz were performed in order to investigate off-center rattling motion of rare-earth ions. The elastic constant C-11 exhibits double ultrasonic dispersions at similar to 15 and similar to 40 K, which are similar to the features found in NdOs4Sb12. The estimated activation energy E-1 = 240 K corresponding to the 40 K-dispersion, possesses an intermediate value between PrOs4Sb12 (E-1 = 115 K) and NdOs4Sb12 (E-1 = 337 K). (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2009.07.081

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Low-temperature elastic properties of the clathrate compound Ce3Pd20Si6 were investigated using ultrasonic measurements. Pronounced softening of elastic constants (C-11 - C-12)/2 and C-44 with decreasing temperature indicates a precursor of electric quadrupole ordering due to it Gamma(8) quartet ground sate with an orbital degeneracy for 8c site of it Ce ion. A minimum of (C-11 - C-12)/2 at T-C = 170 mK indicates a transition from paramagnetic phase I to an ordered phase III. Applied magnetic fields induce an antiferro-quadrupole (AFQ) ordered phase II with highly anisotropic character depending on the field direction, which resembles the AFQ phase with O-xy-type order parameter in CeB6 with the Gamma(8) ground sate. The order parameter of the phase III may be characterized by either magnetic dipole or magnetic octupole. The Gamma(7) ground state at 4a site may fall into it singlet screened by conduction electrons at low temperatures Without long-range magnetic ordering.

DOI： 10.1143/JPSJ.78.024716

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Using a low temperature x-ray diffractometer, we studied superconductivity materials, optimally doped and underdoped YBCOs and PrOs(4)Sb(12) between 0.1 K and 300 K. At several temperatures, whole profiles of the x-ray reflection peak were measured and refined by Rietveld analysis. By Rietveld analysis, we found that Pr atoms in PrOs(4)Sb(12) are still oscillating at an amplitude of about 0.1 angstrom at 0.18 K. For some reflection planes, x-ray diffraction measurement with a small step size and a long stepping time was performed to accumulate more counts at certain temperatures. The lattice constant d of optimally doped YBCO (OPT YBCO) shows anomalous behaviours at around the superconductivity transition temperature Tc and around spin gap temperature T*. In OPT YBCO, the intensity of the reflection spectrum shows a clear anomaly at around Tc.

DOI： 10.1088/1742-6596/150/5/052284

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According to conventional theories of strongly correlated electron systems, the natural consequence of strong hybridization between f-electrons and conduction electrons is the opening of a gap in both charge and spin channels. Despite their importance, there are few experimental observations of such gaps in real materials. Recently the charge gap in d- and f-electron systems has been investigated using optical studies. However, due to the q=0 limitation of the technique, optical studies cannot give information on the wave vector dependence of the gap. Inelastic neutron scattering is a unique technique and provides direct information on the spin gap energy as well as its wave vector and temperature dependence. Further, knowledge of the wave vector dependence of the gap, in particular the spin gap, provides important information about the microscopic mechanism of the gap formation. Recently we have investigated the spin gap formation, and its relation to the charge gap, in several Ce, Yb and U based compounds using inelastic neutron scattering techniques. We review here the nature of the spin gap in CeT4Sb12 (T = Ru, Os and Fe), CeRhAs and U2-xThxRu2Sn compounds based on our recent neutron scattering studies. We compare the magnitude of the spin gaps we have measured in this way with that of the charge gaps measured in optical studies. We have found a universal scaling relation between the spin gap energy and the Kondo temperature (T-K) for many strongly correlated electron systems and the results are discussed.

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We report nuclear quadrupole resonance (NQR) studies on Ru-sites of filled skutterudite compounds RRuR12 (R = La, Nd, Sm) in zero magnetic field. For NdRu4P12, the Ru-101-NQR signal disappears below T-C = 1.6 K, which is indicative of the transformation into the ferromagnetically ordered ground state. For SmRu4P12, a single Ru-101-NQR line splits into two lines below the metal-insulator transition temperature T-MI = 16.5 K with the intensity ratio of 3 : 1. This result gives evidence that there are two inequivalent Ru-sites with different electric field gradient. The intensity ratio leads to a conclusion that the symmetry is lowered below T-MI from a cubic Im (3) over bar space group to a trigonal M one. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2007.10.205

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We have carried out nuclear quadrupolar resonance (NQR) measurements on SmRu4P12 and YbAl3C3, both of which have attracted much interest in terms of multipolar ordering. Although no structural anomalies have been detected by diffraction experiments so far, the NQR resonance frequencies v(Q)'s of both compounds show marked anomalies just below each phase transition temperature, which probably probes the order parameters. The results provide important information to shed light on the ordered structures in the low temperature phases of these compounds. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2007.10.206

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SmFe4P12 is a novel ferromagnetic heavy fermion compound with a Curie temperature Tc of 1.6K. The electronic specific heat coefficient is 370 mJ/mol·K2. The magnetic susceptibility of La1-xSmxFe4P12 (0.6 ≤ x ≤ 0.85) with a paramagnetic ground state shows a broad maximum around 15K. This phenomenon reminds us the case of CeRu2Si 2 which is in the boundary of itinerant and localized 4f-state. We measured the magnetization up to 42T and found metamagnetic crossover at 22T. The metamagnetism disappears with increasing temperature. Possible mechanism of the metamagnetism is discussed. ©2008 The Physical Society of Japan.

DOI： 10.1143/JPSJS.77SA.209

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DOI： 10.1016/j.jmmm.2006.10.329

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From the measurements of magnetization and specific heat, we constructed B-T phase diagrams of single-crystalline DyPd3S4 which is known to exhibit antiferroquadrupolar (AFQ) and antiferromagnetic (AFM) ordering at low temperatures. The phase diagrams are found to be highly anisotropic and reentrant, which are typical of rare-earth compounds exhibiting multipolar ordering. The crystalline electric field (CEF) scheme of Dy3+ in DyPd3S4 was deduced from the specific heat and magnetization measurements of the Y-diluted compounds Dy1-xYxPd3S4 (0.1 <= x <= 0.9) and discussed in detail. The CEF ground state was determined to be the orbitally-degenerated quartet 17670), and the overall splitting width was estimated to be about 104 K. No correlation was found between the anisotropy of To and that of the Zeeman splitting width of the ground quartet Gamma((1))(67).

DOI： 10.1143/JPSJ.76.084717

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We report the results of NQR (nuclear quadrupole resonance) study on SmRu4P12, one of a few candidates for materials showing octupolar ordering. In this study, we firstly succeeded in observing the Ru-101-NQR signal in filled skutterudite compounds RRu4P12 (R: rare earth). A single Ru-101-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 Im(3) over bar space group for the filled skutterudite compounds is lowered to the trigonal R(3) over bar. 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.

DOI： 10.1143/JPSJ.76.043714

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In order to investigate the microscopic origin of the transitions at T-MI similar to 16.5K and T* similar to 14K in filled skutterudite compound SmRu4P12, we have carried out P-31-NMR measurements using a single crystal sample. The drastic change in the NMR line-shape below TMI was observed, which is attributed to the occurrence of some long-range magnetic ordering. The order is probably associated with octupole ordering as indicated from the NMR measurements on the powder sample of SmRu4P12. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.128

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We have studied the crystalline electric-field effect of the noncentrosymmetric heavy-fermion antiferromagnet CeRhSi3 by measuring the magnetic susceptibility chi(T), specific heat C-p(T) and inelastic neutron scattering. The 4f level scheme determined from X agrees with a magnetic excitation observed in the inelastic neutron spectra and the Schottky anomaly in the magnetic part of C, Moreover, we have measured C, under various magnetic fields B up to 8 T and observed that the Neel temperature T-N decreases proportionally to B-2 for B || a-axis while the B dependence of T-N is rather small for B || c-axis. This anisotropic behavior suggests that the antiferromagnetically ordered moments lie in the tetragonal c-plane.

DOI： 10.1143/JPSJ.76.033706

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Raman scattering of skutterudite compounds RT4 X12 (R = La, Ce, Pr, Nd, Sm and Yb, T = Fe, Ru and Os, X = P and Sb) have been measured. All first-order Raman active phonons are observed and are assigned as the pnictogen vibrations. At the low energy region, the second-order phonons, including the vibration of the rare-earth ions with a flat phonon dispersion, are observed in the spectra of SmRu4 P12 and ROs4 Sb12. The second-order phonons can be observed for the sample with the larger cage space. The large displacement in the large cage space and the large density of state due to the flat phonon dispersion increase the intensity of the second-order Raman scattering process. The intensity of the second-order phonon are also affected by the valence of the rare-earth ions. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.159

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The optical conductivity of the Kondo insulator compound CeOs(4)Sb(12) reveals the formation of a 70 meV charge gap below 160 K. It also exhibits a weak shoulderlike structure at 30 meV, below 60 K. We have investigated CeOs(4)Sb(12) by inelastic neutron scattering techniques using incident neutron energies (E(i)) of 23 and 200 meV, at 5 and 176 K. Our measurements with E(i) = 200 meV show magnetic scattering centered near 50-60 meV and low-Q (similar to 3.8 angstrom(-1)) at 5 K, in addition to the continuum of magnetic scattering observed at 176 K. This clearly indicates the opening of a spin gap (or pseudogap ) of the order of 50 meV at 5 K in the strongly renormalized band near the Fermi energy. Furthermore, measurements with E(i) = 23 meV did not reveal any evidence of magnetic excitations below 20 meV, consistent with the scenario of a spin gap in CeOs(4)Sb(12). However, the estimated magnetic scattering deduced from the E(i) = 200 meV data reveals the presence of broad magnetic scattering between 25 and 80 meV centered near 27 meV, indicating a second energy scale with a gap energy of 27 meV. We interpret the 50 meV energy scale in terms of a direct gap, while the 27 meV energy scale corresponds to an indirect gap across the two hybridized bands. This gap energy of 27 meV is in good agreement with the so-called universal energy scale versus single ion Kondo temperature plot. We present the general features of spin gap systems such as CeOs(4)Sb(12) and CeRu(4)Sb(12), and discuss the role of crystal field excitations regarding the spin gap formation based on a theoretical model.

DOI： 10.1103/PhysRevB.75.014418

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DOI： 10.1143/JPSJ.75.093706

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We have investigated an off-center local oscillator of a guest atom in cage of clathrate compounds R3Pd20Ge6 (R = La, Ce, Pr, Nd) and a filled skutterudite PrOs4Sb12 using ultrasonic measurements. The observation of ultrasonic dispersions in transverse C-44 mode of R3Pd20Ge6 and in transverse (C-11 - C-12)/2 mode of PrOs4Sb12 revealed the rattling of the off-center oscillator characterized by a relaxation time with Arrhenius-type temperature dependence. A low-temperature softening of C-44 in La3Pd20Ge6 below 3 K down to 20 mK and a softening of (C-11 - C-12)/2 in PrOs4Sb12 above the heavy Fermion superconducting transition indicate the charge fluctuation due to the degenerate off-center oscillators. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.03.071

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Raman scattering spectra of filled skutterudite RT4X12 (R = La, Ce, Pr, Nd, Sm and Y, T = Fe, Ru and Os, and X = Sb and P) and unfilled skutterudite CoP3 have been measured. All first-order Raman active phonons, which are due to the vibration of pnictogens, are observed. In addition, the crystal field excitations in PrRu4P12 spectra and the second-order phonons including rare-earth vibrations in SmRu4P12 and ROs4Sb12 are also observed. The second-order phonons can be observed for the sample with the larger cage space. The peak intensity of the second-order phonons decreases with decreasing temperature and vanishes at low temperature. Such a temperature dependence suggests that the second-order phonons are thermally excited and due to independent vibrations of the rare-earth ions, that is rattler motion. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.03.076

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To elucidate microscopically the metal-insulator transition (T-MI similar to 16.5 K) and an additional transition (T* similar to 15 K) in Sm-based filled skutterudite compound SmRu4R12, we have carried out P-31-NMR (nuclear magnetic resonance) at various fields from 0.8 to 11 T. The peaks in the spin lattice relaxation rate 1/T-1 observed at T-MI and T* under similar to 7T indicate that there are different magnetic fluctuation modes in SmRu4P12: one freezes below T-MI and the other does below T*. The anomalous field and temperature dependences of the NMR spectrum are explained in terms of the occurrence of multipole ordering. We have examined the two possible scenarios to account for the experimental results, and both cases suggest that the M-I transition involves octapole ordering.

DOI： 10.1143/JPSJ.75.053708

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Ultrasonic attenuation measurements have been firstly performed for a large single crystal of PrOs4Sb12 with the dimensions of 5.97 x 0.6 x 0.6 mm(3). Remarkable frequency dependence around 20-40K has been observed in the elastic constant and attenuation coefficient of the longitudinal C-11 mode associated with E-g symmetry strain in part, which results from a thermally activated off-center rattling with E-g symmetry of a Pr ion inside a Sb icosahedron cage. Parameters of a characteristic time tau(0) = 3.1 x 10(-11) s and an activation energy E = 225 K were obtained. This E-g rattling involving a local charge fluctuation inside a Sb cage periodically arranged may couple to the conduction electrons. As a result, the electron-phonon coupling would lead to heavy fermion and its superconductivity in PrOs4Sb12. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.01.070

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We have carried out P-31-NMR (nuclear magnetic resonance) studies on Sm-based filled skutterudite compounds SmRu4P12. The measurements of NMR spectrum at various fields (H's) give evidence that spontaneous internal field occurs below the metal-insulator transition temperature T-M1 similar to 16.5 K. Concomitantly H-induced local field was observed between two successive transition temperatures, T* (similar to 14K) < T < T-M1, suggesting that some multipole ordering coexists with dipole ordering in this compound. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.01.083

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We report a comprehensive infrared magnetospectroscopy study of a CeRu4Sb12 compound revealing quasiparticles with a heavy effective mass m(*), with a detailed analysis of optical constants in fields up to 17 T. We find that the applied magnetic field strongly affects the low-energy excitations in the system. In particular, the magnitude of m*similar or equal to 70 m(b) (m(b) is the quasiparticle band mass) at 10 K is suppressed by as much as 25% at 17 T. This effect is in quantitative agreement with the mean-field solution of the periodic Anderson model augmented with a Zeeman term.

DOI： 10.1103/PhysRevLett.96.017403

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We have investigated the magnetic penetration depth lambda and the superconducting coherence length xi in the vortex lattice of the filled skutterudite compound PrRu4Sb12 (T-c similar to 0.97 K) using transverse-field muon-spin rotation measurements. Zero-field and longitudinal-field studies were also carried out to investigate the time-reversal symmetry of the superconducting state. We found lambda=3650(20) angstrom and xi=345(5) angstrom at 0.05 K and using these values of lambda and xi, together with the Sommerfeld constant we have calculated an effective mass of the quasiparticles m(*)approximate to 10m(e) and superfluid carrier density n(s)approximate to 4x10(27) carriers/m(3). The temperature dependence of the vortex state muon-spin relaxation rate sigma(s)(T) is consistent with the phenomenological two-fluid model. Further, the zero-field and longitudinal field measurements do not reveal any signature of a spontaneous internal magnetic field below the superconducting transition temperature, indicating the preservation of time-reversal symmetry in the superconducting state of PrRu4Sb12, unlike the broken time-reversal symmetry of the superconducting state of the heavy-fermion superconductor PrOs4Sb12.

DOI： 10.1103/PhysRevB.72.184503

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We measured the specific heat C-p of an annealed sample of CePt3Si in magnetic fields B up to 10 T and confirmed two conspicuous anomalies in the temperature range where no apparent magnetic anomalies were found in the susceptibility. The lower-temperature anomaly at 2.2 K was depressed with increasing B and seemed to get absorbed around 4 T into the other one around 2.8 K. The latter anomaly continues to grow into a solid peak with increasing B. These features imply that neither of these transitions is due to long-range antiferromagnetism (AF) as originally proposed, but they are reminiscent of quadrupolar transitions found in certain Ce-based Kondo compounds, in which two distinct anomalies were also observed in C-p and identified as a quadrupolar transition followed by an AF transition at a slightly lower T. In the case of CePt3Si, the lower-T anomaly is not due to AF but to a new phase transition of yet-unknown nature, and in this new phase the superconductivity emerges at 0.8 K. We thereby hypothesize that the superconductivity could be mediated by magnetic or other electronic excitations under the influence of the quadrupolar-like order induced around 2.8 K and that CePt3Si would be the first example of an unconventional superconductor coexisting with electric-multipolar order.

DOI： 10.1088/0953-8984/17/23/L02

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We report the results of P-31 NMR measurements on YFe4P12, a new member of the family of the filled skutterudite compounds, which displays superconductivity below T-c = 7 K. In the normal state, the nuclear spin-lattice relaxation time T-1 obeys the Korringa relation T1T = constant below 40 K, but it changes its behavior at higher temperatures. The Korringa constant (T1T)(-1) for YFe4P12 is smaller than that for LaFe4P12, suggesting that the density of states at Fermi energy N(E-F) for YFe4P12 is lower than the case of LaFe4P12. In the superconducting state, T-1(-1)(T) shows a small coherence peak just below Tc, followed by an exponential decrease below 4 K revealing on energy gap 2 Delta(0)/k(B)T(c) = 3.3. Our results indicate that YFe4P12 is a conventional type s-wave superconductor. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.01.333

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We have determined the crystal field potential of the superconductor PrRu(4)Sb(12) (T(c) similar to 0.9 K) using inelastic neutron scattering. The ground state of the Pr(+3) ions in T(h) point group symmetry is a Gamma(1) singlet with a Gamma(5) triplet at an energy of Delta similar to 5.6meV. Comparison with recent results on the PrOs(4)Sb(12) compound, where T(c) similar to 1.85 K and Delta similar to 0.6 meV, supports the conjecture that inelastic quadrupolar fluctuations (or aspherical Coulomb scattering) are responsible for the strong enhancement of T(c). In PrRu(4)Sb(12), the effect is reduced by the higher energy of the first excited level. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.01.286

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We have studied the effect of heat treatment and the Ge substitution in place of Si in the recently discovered heavy-fermion superconductor CePt3Si. The annealed CePt3Si exhibited nonmagnetic heavy-fermion behavior instead of the antiferromagnetism (AF) found in quenched samples. The AF state was destroyed by only about 1 at.% of Ge-substitution and may not be a stable phase. Specific-heat measurements on the annealed CePt3Si and the Ge-substituted samples revealed a large hump around 2.2 K, originally claimed as Neel temperature. Its true nature is not clarified yet but conjectured at present as a sort of quadrupolar transition rather than AF long-range order. The superconducting transition around 0.75 K was equally sharp with DeltaC(P)/gammaT(c) = 0.7 for clean quenched and annealed samples. The interplay between the 2.2 K-anomaly and the superconductivity is discussed. (C) 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ssc.2004.10.032

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.60.1.3.0_497_4

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We report on the magnetic susceptibility, specific heat and electrical resistivity of the heavy fermion compounds CeNiGe2-xSix (0 less than or equal to x less than or equal to 1). Compounds with x < 1 show anti ferro magnetic order, which with increasing x shifts toward lower temperature owing to increased exchange coupling between the localized 4f magnetic moments and conduction electrons. Eventually, the magnetic order almost becomes absent, for x = 1. An anomaly observed in the specific heat is well interpreted by the Kondo model for a degenerate impurity spin J = 1/2 in the Coqblin-Schrieffer limit. A coherence peak indicative of the formation of a Kondo lattice is found in the electrical resistivity, whose features are consistent with the results for the specific heat. Interestingly, there is a significant deviation from Fermi-liquid behaviour at the critical concentration x = 1. This deviation is attributed to a quantum phase transition in a model with two-dimensional antiferromagnetic fluctuations.

DOI： 10.1088/0953-8984/16/46/018

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We present the magnetic properties of a filled skutterudite La1-xSmxFe4P12. SmFe4P12 is a heavy ferimon compound with a novel ferromagnetic ground state. The magnetic susceptibility for x less than or equal to 0.4 shows a nearly temperature-independent Pauli paramagnetism, but samples for 0.6 less than or equal to x less than or equal to 0.85 reveals a broad maximum around 15 K. The origin of the maximum is discussed. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.058

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We have investigated the temperature and momentum dependence of the inelastic neutron scattering response of CeRu4Sb12. Our neutron scattering study shows the opening of a Q-independent spin gap of 30 meV in the excitation spectrum, which is smaller than the charge gap of 47 meV observed in optical studies. The spin gap is nearly temperature independent below 100 K, while above this temperature the gap starts to fill up and at higher temperatures the magnetic response becomes purely quasielastic. We discuss the origin of the spin gap and consider the difference between the magnitude of the spin and charge gaps on the basis of theoretical models. (C) 2004 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.126

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We have performed electrical resistivity measurements at different pressures on two kinds of samples (low-T-c and high-T-c), which differ in physical properties of the heavy-fermion superconductor CeCu2Si2. It was found that one with lower T-c shows partial derivative T-c/partial derivative P of negative and the other with higher T-c shows partial derivative T-c/partial derivative P of positive. Therefore, the superconductivity for these two samples may have different origins. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.103

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DOI： 10.1016/S0921-4526(02)02031-8

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The platelike crystals of a series of novel molecular conductors, which are based on the pi-donor molecules BDT-TTP (2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene) with a tetrathiapentalene skeleton and lanthanide nitrate complex anions [Ln(NO3)(x)](3-x) (Ln = La, Ce, (Pr), Tb, Dy, Ho, Er, Tm, Yb, Lu) with localized 4f magnetic moments, were synthesized. Except for the Ce complex, the salts were composed of (BDT-TTP)(5)[Ln(NO3)(5)] and were isostructural. Even though the Ce crystal had a different composition, (BDT-TTP)(6)[Ce(NO3)(6)](C2H5OH)(x) (x approximate to 3), the crystals all had the space group P (1) over bar. Although the X-ray examination of the Pr salts was insufficient, the existence of two modifications was suggested in these systems by preliminary X-ray examination. Previously, we reported the crystal structures and unique magnetic properties of (BDT-TTP)(5)[Ln(NO3)(5)] (Ln = Sm, Eu, Nd, Gd). Thus, by combining the results of this work with previous one, we for the first time succeeded in obtaining a complete set of organic conductors composed of the identical pi-donors (BDT-TTP in this case) and all the lanthanide nitrate complex anions (except the complex with Pm3+). The crystals were all metallic down to 2 K. Electronic band structure calculations resulted in two-dimensional Fermi surfaces, which was consistent with their stable,metallic states. Except for the Lu complex, which lacked paramagnetic moments, the magnetic susceptibilities were measured on the six heavy lanthanide ion complex salts by a SQUID magnetometer (Ln = Tb, Dy, Ho, Er, Tm, Yb). The large paramagnetic susceptibilities, which were caused by the paramagnetic moments of the rare-earth ions, were obtained. The Curie-Weiss law fairly accurately reproduced the temperature dependence of the magnetic susceptibilities of (BDT-TTP)(5)[Ho(NO3)(5)] in the experimental temperature range (2-300 K) and-a comparatively large Weiss temperature (\Theta\) was obtained (Theta(Ho) = -15 K). A Weiss temperature (Theta(Tm) = -8 K) was also obtained for Tm. The \Theta\ values of other (BDT-TTP)(5)[Ln(NO3)(5)] salts and (BDT-TTP)(6)[Ce(NO3)(6)](C2H5OH)(x)(x approximate to 3) were as follows: \Theta\/K = 4 (Er), less than or equal to2 (Ce, Tb, Dy, Yb). The comparatively strong intermolecular magnetic interaction between Ho3+ ions, which was suggested by the \Theta\ value, is inconsistent with the traditional image of strongly localized 4f orbitals shielded by the electrons in the outer 5s and 5p orbitals. The dipole interactions between Ln(3+) ions causing the Curie-Weiss behavior and the comparatively large Theta value of (BDT-TTP)(5)[Ho(NO3)(5)] is inconsistent with the data, since the complexes exhibit isostructural properties and there is not a clear relationship between the magnitudes of Theta values and those of magnetic moments. Therefore, it is possible that the 4f orbitals of Ho atom are sensitive to the ligand field, which will have an effect on the orbital moment of the Ho3+ ion and/or produce a small amount of mixing between 4f and ligand orbitals to give rise to "real" intermolecular antiferromagnetic interaction through intermolecular overlapping between pi (BDT-TTP) and ligand orbitals of lanthanide nitrate complex anions.

DOI： 10.1021/ic034459g

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A new filled skutterudite YFe4P12 has been prepared at high temperatures and high pressures. The electrical resistivity and dc magnetic susceptibility of this compound were measured at low temperatures. The superconductity in YFe4P12 is observed at around 7 K. This phosphide is a new superconductor. The specific heat of YFe4P12 has been studied between 2 and 20 K. The specific heat fitted to the expression C = γT + βT3, by a least squares analysis, yielded the values γ = 27.2 mJ mol-1 K-2 and β= 0.195 mJ mol-1 K-4. The Debye temperature (ΘD) is found to be 553 K. The electronic density of the states at the Fermi energy for YFe4P12 is 0.45 state eV-1/atom.

DOI： 10.1088/0953-8984/15/28/352

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The specific heat in low temperature regions was measured for several pseudoternary compounds of the CeNiGe2-xSix System. Substitution of silicon for germanium enhances the coupling constant J and the Kondo interaction. The antiferromagnetism in CeNiGe2 is ultimately suppressed around x = 1 by the enhanced Kondo effect. A non-Fermi liquid behavior has been observed in x = 1 composition. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02211-1

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We report on the magnetic properties of a filled skutterudite compound, SmFe4P12. Magnetic susceptibility and specific heat measurements revealed a ferromagnetic transition at 1.6 K. The temperature dependence of the electrical resistivity exhibits a Kondo-lattice behaviour and the electronic specific heat coefficient attains values as large as 370 mJ mol-1 K-2. This compound is thereby the first Sm-based heavy-fermion system found with a ferromagnetic ground state. The Kondo temperature is estimated to be about 30 K.

DOI： 10.1088/0953-8984/15/14/101

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We have recently reported our finding of a weakly ferromagnetic phase and two superconducting phases in the Cu-deficient and Cu-rich region of the homogeneity range, respectively, for the heavy-electron compound CeCu2Si2. We herein report more detailed results of the specific heat, magnetic susceptibility, resistivity (R), magnetoresistance (ΔR) and thermopower for many different compositions. We confirmed the slightly re-entrant behavior in the Hc2(T) curve and a change of regime in the ΔR at about 0.35 K above Hc2(T) for the low-Tc phase. Above about 0.75 K, the normal state of this phase exhibited no magnetoresistance up to 70 kOe, while that of high-Tc phase and the weakly ferromagnetic phase did a slightly positive ΔR. These differences in the three phases may provide an important clue to better understanding of the heavy-electron superconductivity of CeCu2Si2. © 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(02)00120-8

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Ultrahigh-resolution photoemission spectroscopy reveals the crossover behavior of CeRu4Sb12 into a low carrier state. The density of states (DOS) around the Fermi level (EF) decreases on lowering the temperature. The temperature dependence of the DOS at EF is consistent with the results of the transport measurements and explained in terms of the development of the coherence. © 2002 Published by Elsevier Science Ltd.

DOI： 10.1016/S0022-3697(02)00019-7

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Ultrahigh-resolution photoemission spectra of (formula presented) reveal crossover behavior into a low carrier state. The density of states (DOS) around the Fermi level (formula presented) decreases on lowering temperature and the semimetalliclike DOS is observed at 5.9 K. The temperature dependence of DOS at (formula presented) is explained in terms of the development of the coherence. The smaller hybridization strength between the Ru- (formula presented) state and the (formula presented) state prevents the hybridization gap from opening in (formula presented) which is realized in (formula presented). © 2002 The American Physical Society.

DOI： 10.1103/PhysRevB.65.041105

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Dinuclear oxovanadium(IV) complexes bridged by pyrimidine derivatives, L[VO(hfac)(2)](2) [L = pyrimidine (PM), 4-methylpyrimidine (MPM), 4,6-dimethylpyrimidine, 4-aminopyrimidine, and quinazoline; hfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dionate], were synthesized and characterized. All of them showed intramolecular ferromagnetic interaction, and the magnetic susceptibilities were analyzed on the basis of the singlet-triplet model, giving 2J/k(B) = 2.2-5.5 K. PM[VO(hfac)(2)](2) crystallized in a monoclinic space group C2/c with a = 34.092(2), b = 6.9783(4), and e = 16.4940(9) Angstrom, beta = 109.104(1)degrees, V = 3707.8(4) Angstrom (3), and Z = 4 for C24H8F24N2O10V2, and MPM[VO(hfac)(2)](2) gave isomorphous crystals. A semiempirical calculation study based on the determined structure suggests the presence of d pi -p pi interaction between vanadium and pyrimidine nitrogen atoms. Ferromagnetic coupling is explained in terms of a spin-polarization mechanism across the pyrimidine bridge. The intermolecular ferromagnetic interaction of PM[VO(hfac)(2)](2) call be interpreted by the contact between the spin-polarized pyrimidine moiety and the oxovanadium oxygen atom in an adjacent molecule.

DOI： 10.1021/ic010730n

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CeRu4Sb12 with the filled skutterudite structure exhibits a novel non-Fermi-liquid (NFL) behaviour in the low-temperature specific heat and electrical resistivity at ambient pressure. We investigated the effect of La substitution and magnetic field on the NEL state and found that it can be easily destroyed either by the application of a magnetic field or by a small degree of La substitution. In magnetic fields, CIT becomes strongly depressed and nearly constant below 1 K and rho (T) turns to following a T-2-law, implying that the Fermi-liquid state recovers in high magnetic fields. The type of critical fluctuation is discussed on the basis of the results of magnetic susceptibility, electrical resistivity and specific heat measurements.

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We present a report on crystalline-electric-field effects observed in the electrical resistivity and the specific heat of Ce3Pd20Ge6, which are discussed within an energy level scheme of the Γ8 ground state and the Γ7 excited state at 50 K for both inequivalent crystallographic sites of Ce atom.The third-order magnetic susceptibility was deduced from the magnetization measurement in the paramagnetic phase of a single-crystalline sample in magnetic fields applied along [0 0 1] and [1 1 1].In order to explain the temperature dependence of the third-order magnetic susceptibility along [0 0 1], a positive total quadrupolar pair interaction constant of 22 mK is required in addition to a small antiferromagnetic exchange interaction, thereby suggesting ferroquadrupolar ordering with the Γ3 symmetry in this compound.

DOI： 10.1143/JPSJ.69.883

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We report a Jahn-Teller-like phase transition in a synthesized metallic compound, TmPd3S4, of the cubic NaPt3O4 structure type. The transition causes a very large thermal hysteresis in the electrical resistivity between 120 and 230 K and a modulated structure with a modulation vector of about 1/8a* (a*: reciprocal-lattice unit vector) at lower temperatures which was revealed by a low-temperature x-ray powder diffraction. Analyses on the low-temperature specific heat and the magnetic susceptibility suggest that the compound becomes an exchange-induced moment antiferromagnet (T-N=1.1 K) by the nonmagnetic singlet ground state of Tm3+ ions. [S0163-1829(99)51146-6].

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DOI： 10.1016/S0921-4526(98)01166-1

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We present the temperature dependence of the magnetic susceptibility χ(T), electrical resistivity ρ(T) and low-temperature specific heat C(T) of CeRu4Sb12. χ(T) shows a broad peak around 100 K characteristic to intermediate-valence compounds but the small Weiss temperature of -26 K and ρ(T) suggest that the compound is classified as a Kondo compound. The ground state is very anomalous and non-Fermi liquid behaviors were observed in C/T and ρ(T) at low temperatures. © 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(98)01167-3

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From the measurement of the specific heat of single crystalline samples of (Formula presented) we have constructed magnetic phase diagrams for a magnetic field up to 4 T, which disclose a pronounced anisotropy along the three principal directions of [100], [110], and [111]. We have found that both the quadrupolar and antiferromagnetic ordering temperatures exhibit distinct directional dependences on the external magnetic field and that new phase transitions evolve in the antiferromagnetic phase as well as in the ordered quadrupolar phase. These facts strongly suggest the existence of a complicated form of anisotropic interaction between the electric quadrupolar moment and the magnetic dipolar moment. The present result is briefly discussed in comparison with the reported one for (Formula presented). © 1998 The American Physical Society.

DOI： 10.1103/PhysRevB.57.7450

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Several pseudoternary compounds of the CeCoGe3-xSix system were studied by magneticsusceptibility, electrical-resistivity and specific-heat measurements. Substitution of silicon for germanium generates the normal chemical pressure and enhances the exchange interaction. The antiferromagnetism in CeCoGe3 is ultimately suppressed around x = 1.2 by the enhanced Kondo effect. Non-Fermi liquid-like behavior has been observed around the critical concentration and an intermediate-valence regime with a very high Kondo temperature of the order of 900 K is followed farther on in the silicon rich region.

DOI： 10.1143/JPSJ.67.2495

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Nitronyl nitroxide derivatives carrying a hydroquinone or a resorcinol moiety 2-(2',5'-dihydroxyphenyl)4,4,5,5-tetramethyl-4,5-dihydro-1H- imidazolyl-1-oxyl-3-oxide (HQNN) and 2-(3',5'-dihydroxyphenyl)-4,4,5,5- tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl 3-oxide (RSNN)) have been designed and prepared. These compounds were found to afford hydrogen-bonded crystals. In the case of HQNN, two phases of crystals (α- and βHQNN) were obtained. Of these, the crystal structure of α-HQNN is characterized by the intramolecular hydrogen bond between the o-hydroxy group and the nitronyl nitroxide and by the intermolecular one-dimensional hydrogen-bonded chain between the o- and p-hydroxy groups of the neighboring molecules, respectively. Two of the hydrogen-bonded chains run in parallel, and they are connected by the bifurcated hydrogen bonds formed between the o-hydroxy groups of the facing molecules in the individual chain. The χT value of this crystal increased monotonously with lowering temperature (ST model, J = +0.93 K, Θ= +0.46 K) and turned out to exhibit a ferromagnetic phase transition at 0.5 K. On the basis of the heat capacity data, α-HQNN was found to be a three-dimensional ferromagnet. On the other hand, the crystal of β-HQNN was characterized by the intermolecular hydrogen-bonded chain formed between the hydroxy group at the meta position and the nitronyl nitroxide and by the interchain π-π stacking. The magnetic interaction of β-HQNN was interpreted by the ferromagnetic ST model, and this ferromagnetic interaction (J = +5.0 K) was accompanied by a weak antiferromagnetic interaction (Θ = - 0.32 K) at lower temperatures. Although the structural feature of the crystal of RSNN resembles that of the β-HQNN, it exhibited the antiferromagnetic interaction predominantly (ST model, J = + 10.0 K, Θ = -4.0 K). These magnetic behaviors are consistent with McConnell's theory, when the spin densities at the interacting sites connected by hydrogen bonds are taken into account. Thus, it may be concluded that the hydrogen bond plays a role not only in constructing hydrogen-bonded crystals but also in transmitting spin polarization along the hydrogen bond.

DOI： 10.1021/ja964083o

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Magnetic and transport properties of the cubic ternary compound (Formula presented)(Formula presented)(Formula presented) are herein reported. The electrical resistivity exhibits the Kondo lattice behavior and a large (Formula presented) coefficient at low temperatures, indicating that this compound is a heavy-electron system with a Kondo temperature of a few degrees Kelvin. The low-temperature specific heat revealed two successive anomalies at (Formula presented) K and (Formula presented) K. The (Formula presented) quartet crystalline-field ground state of Ce ions is conjectured from the thermal variation of magnetic entropy deduced from the specific-heat data. The anomaly at (Formula presented) is probably a result of quadrupolar interaction between (Formula presented) ground states, while the other one at (Formula presented) is due to antiferromagnetic ordering. © 1996 The American Physical Society.

DOI： 10.1103/PhysRevB.53.5101

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The 1 2 spins of oxovanadium(IV) ions were ferromagnetically coupled with J kB = +1.1∼+2.7 K in the dinuclear complexes L[VO(hfac)2]2 (hfac = hexafluoroacetylacetonate, L = pyrimidine derivatives). Among them, a ferromagnetic transition was observed at about 0.14 K in PM[VO(hfac)2]2 (PM = pyrimidine). The polymeric complex QZ[Cu(hfac)2] (QZ = quinazoline) gave a positive Weiss constant (+0.39 K). The ferromagnetic transition was observed at about 0.12 K. © 1995.

DOI： 10.1016/0379-6779(94)03052-8

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The title radicals were found to be bulk ferromagnets, as indicated by the sharp divergence of the susceptibility. Their transition temperatures were found in the range of 0.2-0.4 K. The X-ray crystal structure analysis of the phenyl, biphenylyl, and chlorophenyl derivatives at room temperature revealed that the crystal consisted of an almost two-dimensional network of the N-O sites. In the case of aryl = 2-naphthyl, metamagnetic behavior was observed below about 0.3 K. © 1995.

DOI： 10.1016/0379-6779(94)03063-C

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Magnetic and transport properties of the ternary compound Ce3Pd20Si6 are investigated down to 0.035 k. The temperature dependence of the electrical resistivity indicates that this compound is a new Kondo material. The low-temperature specific heat measurement reveals that C/T is strongly enhanced at low temperatures, reaching as high as 8 J/mole Ce·K2 at 0.2 k. This leads to the conclusion that Ce3Pd20Si6 is one of the heaviest-electron systems. © 1995, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.64.387

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DOI： 10.11316/jpsgaiyoj.1995.3.0_155_2

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The Fermi surface and the cyclotron mass of a semimetallic compound, CeAs, were determined by use of the dHvA effect. We have found that the cyclotron mass of the hole surface decreases with increasing field. CeAs is a dense Kondo system with low carrier concentration of 0.0024/formula unit. © 1993.

DOI： 10.1016/0921-4526(93)90520-G

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We have measured specific heat, magnetic susceptibility and electrical resistivity of UPd2Al3 and UPd2Al3.03 single crystals. The temperature dependence of the specific heat of UPd2Al3 reveals that the superconducting gap function is anisotropic. We present the results of specific heat measurements of UPd2Al3.03, suggesting an additional phase transition around 0.6 K.

DOI： 10.1016/0921-4526(93)90559-O

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Low-temperature specific heat of YbAs has been measured down to about 50 mK. In the antiferromagnetic ordered state (TN∼0.5 K), the nuclear contribution is observed below about 150 mK. By subtraction of this contribution from the measured specific heat, the linear coefficient of the electronic specific heat is estimated to be about 270 mJ/K2 mole. This value is extraordinarily large because the carrier concentration in YbAs is of the order of 0.01 per formula unit. This large mass enhancement may be ascribed to a mutual 4f-spin compensation mechanism instead of the usual Kondo spin fluctuation. We also show that the magnetic field effect on the specific heat is rather small. © 1992, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.61.2209

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We report on the anisotropy of magnetization, electrical resistivity and upper critical magnetic fields (HC2) of UPd2Al3. The magnetization curve in the antiferromagnetically ordered state shows large anisotropy, indicating that the sublattice moments lie in the basal hexagonal plane. The value of 1(dHC2/dT) at Tc is estimated to be about 36 (kOe/K) for the magnetic field parallel and perpendicular to the hexagonal c-axis, and the upper critical field seems to be rather isotropic. © 1992, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.61.32

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We have newly found and succeeded in growing a mass-enhanced ferromagnet U2PtSi3. The electronic specific heat coefficient is 200 mJ/K2 per mole of U. The magnetization shows no saturation up to 80 kOe for both the a- and c-axes. The magnitude of remanence is much smaller compared with the effective moment in the paramagnetic phase. Experimental results on single-crystalline samples are presented and discussed. © 1991, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.60.757

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dHvA magnetization of U3P4 and YbAs has been measured. The measurement for U3P4 in the {1 1 0} plane shows a new branch. We have observed the dHvA effect in YbAs for the first time. The observed branches consist of ellipsoids of electron sheets. These sheets do not change its shape above and below T(N).

DOI： 10.1016/S0304-8853(10)80152-0

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DOI： 10.1016/S0921-4526(99)00990-4

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DOI： 10.1103/PhysRevB.57.7450

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DOI： 10.1016/S0925-8388(96)03020-4

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