Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1038/s41567-020-0927-4

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Other Link： http://www.nature.com/articles/s41567-020-0927-4

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

We have measured the temperature dependence of resistivity in single-crystalline CeNiGe3 under hydrostatic pressure in order to establish the characteristic pressure-temperature phase diagram. The transition temperature to AFM-I phase T-N1 = 5.5 K at ambient pressure initially increases with increasing pressure and has a maximum at similar to 3.0GPa. Above 2.3 GPa, a clear zero-resistivity is observed (SC-I phase) and this superconducting (SC) state coexists with AFM-I phase. The SC-I phase suddenly disappears at 3.7 GPa simultaneously with the appearance of an additional kink anomaly corresponding to the phase transition to AFM-II phase. The AFM-II phase is continuously suppressed with further increasing pressure and disappears at similar to 6.5 GPa. In the narrow range near the critical pressure, an SC phase reappears (SC-II phase). A large initial slope of upper critical field mu H-0(c2) and non-Fermi liquid behavior indicate that the SC-II phase is mediated by antiferromagnetic fluctuations. On the other hand, the robust coexistence of the SC-I phase and AFM-I phase is unusual on the contrary to superconductivity near a quantum critical point on most of heavy-fermion compounds.

DOI： 10.7566/JPSJ.89.063702

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Publishing type：Research paper (international conference proceedings)   Publisher：Journal of the Physical Society of Japan  

DOI： 10.7566/jpscp.30.011030

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Journal of the Physical Society of Japan  

DOI： 10.7566/JPSCP.30.011037

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

Antiferromagnet Mn3P with Neel temperature T-N = 30 K is composed of Mn tetrahedrons and zigzag chains formed by three inequivalent Mn sites. Due to the nearly frustrated lattice with many short Mn-Mn bonds, competition of the exchange interactions is expected. We here investigate the magnetic structure and physical properties including pressure effect in single crystals of this material, and reveal a complex yet well-ordered helimagnetic structure. The itinerant character of this materials is strong, and the ordered state with small magnetic moments is easily suppressed under pressure, exhibiting a quantum critical point at similar to 1.6 GPa. The remarkable mass renormalization, even in the ordered state, and an incoherent-coherent crossover in the low-temperature region, characterize an unusual electronic state in Mn3P, which is most likely effected by the underlying frustration effect.

DOI： 10.1103/PhysRevLett.124.087202

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevLett.124.087202/fulltext

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevb.99.094403

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.99.094403/fulltext

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier B.V.  

We review our 59Co NMR study in a URhGe single crystal doped with 10% cobalt. The spin-spin relaxation time (T2) measurements have revealed a divergence of electronic spin fluctuations in the vicinity of a field-induced tricritical point (TCP) locating around 13 T. The fluctuations is developed in the same limited field region around the TCP as that where a reentrant superconductivity (RSC) is observed in URhGe. The finding strongly suggests these quantum fluctuations as the pairing glue responsible for the RSC.

DOI： 10.1016/j.physb.2017.09.022

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

The effects of pressure on antiferromagnetic (AFM) and superconducting phase transitions of 112-type Ca1-xLaxFeAs2 were studied, and the in-plane electrical resistivity rho(ab) was measured with an indenter-type pressure cell. The AFM phase transition temperatures of T-N = 47, 63, and 63 K at ambient pressure for x = 0.18, 0.21, and 0.26 was suppressed by applying pressure P, with superconductivity emerging at critical pressures of P-c similar or equal to 0, 1.5, and 3.4 GPa, respectively. Correspondingly, the slope of T-N against P decreased as dT(N)/P similar or equal to -15 and -2K/GPa for x = 0.21 and 0.26, respectively. Thus, although the AFM phase was stabilized with La doping x, the AFM phase was suppressed by pressure, and superconductivity eventually emerged.

DOI： 10.7566/JPSJ.86.113705

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

The ferromagnetic superconductor URhGe has been known to exhibit an extremely large enhancement of the upper critical field when the field is confined and rotated in the (ab) crystal plane. Our high-field Co-59 NMR measurements on 10% Co-doped URhGe up to 30 T prove that this unconventional behavior of the superconductivity (SC) is associated with a strong anisotropy of field-dependent quantum fluctuations near a tricritical point. These fluctuations are rapidly suppressed by the field component along the c axis, while being unaffected by any field component along the a axis. The observed close interplay between the SC and quantum fluctuations strongly supports a pairing mechanism mediated by these fluctuations in URhGe.

DOI： 10.1103/PhysRevB.93.201112

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Publishing type：Research paper (international conference proceedings)   Publisher：IOP Publishing  

DOI： 10.1088/1742-6596/683/1/012010

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Other Link： http://stacks.iop.org/1742-6596/683/i=1/a=012010?key=crossref.b63b036c2e19b193555f0a2b03be6a7c

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

We succeeded in growing single crystals of SrAl4 and related compounds with the BaAl4-type tetragonal structure by the self-flux method, and measured the electrical resistivity, magnetic susceptibility, Hall coefficient, thermoelectric power, and de Haas-van Alphen (dHvA) effect. A plausible characteristic feature of the charge density wave (CDW) was observed below T-CDW = 243 K in SrAl4. We also studied an effect of pressure on the electronic state in SrAl4 by measuring the electrical resistivity and thermoelectric power. T-CDW is found to decrease with increasing pressure, with a rate of dT(CDW)/dP = -12.5 K/GPa. To clarify the Fermi surface nesting, we studied the Fermi surface in SrAl4, which is found to be different from the Fermi surfaces of the similar compounds SrGa4, BaGa4, and BaAl4 without CDW. The Fermi surfaces in these compounds were determined from the dHvA experiments, together with the energy band calculations. (C) 2015 Published by Elsevier B.V.

DOI： 10.1016/j.jallcom.2015.08.193

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The temperature dependence of the Hall coefficient of CeIn3 under high pressure has been investigated. The absolute value of the Hall coefficient shows an anomalous increase below T* similar to 80K at ambient pressure. The increase in T* with increasing pressure is similar to the pressure dependence of the characteristic temperature where the resistivity reaches its maximum. The temperature variations below T* at various pressures are well scaled on a single curve that is the formula based on the two-fluid model. No effect of the antiferromagnetic fluctuations observed in CeTIn5 (T = Co, Rh, and Ir) is observed above 2K even near the critical pressure where antiferromagnetic ordering disappears.

DOI： 10.7566/JPSJ.84.123702

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

The mineral tetrahedrite Cu12Sb4S13 exhibits a first-order metal-insulator transition (MIT) at T-MI = 85K and ambient pressure. We measured the 63Cu-NMR at ambient pressure and the resistivity and magnetic susceptibility at high pressures. Cu-63-NMR results indicate a nonmagnetic insulating ground state in this compound. The MIT is monotonically suppressed by pressure and disappears at similar to 1.0 GPa. Two other anomalies are observed in the resistivity measurements, and the pressure-temperature phase diagram of Cu12Sb4S13 is constructed.

DOI： 10.7566/JPSJ.84.093701

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

Our measurements of the Co-59 NMR spin-spin relaxation in URh0.9Co0.1Ge reveal a divergence of electronic spin fluctuations in the vicinity of the field-induced quantum critical point at H-R approximate to 13 T, around which reentrant superconductivity (RSC) occurs in the ferromagnetic heavy fermion compound URhGe. We map out the strength of spin fluctuations in the (H-b; H-c) plane of magnetic field components and show that critical fluctuations develop in the same limited region near the field HR as that where RSC is observed. This strongly suggests these quantum fluctuations as the pairing glue responsible for the RSC. The fluctuations observed are characteristic of a tricritical point, followed by a phase bifurcation toward quantum critical end points.

DOI： 10.1103/PhysRevLett.114.216401

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

The pressure dependence of the superconducting transition temperature (T-c) and unit cell metrics of tetragonal (NH3)(y)Cs0.4FeSe were investigated in high pressures up to 41 GPa. The T-c decreases with increasing pressure up to 13 GPa, which can be clearly correlated with the pressure dependence of c (or FeSe layer spacing). The T-c vs. c plot is compared with those of various (NH3)(y)MxFeSe (M: metal atoms) materials exhibiting different T-c and c, showing that the T-c is universally related to c. This behaviour means that a decrease in two-dimensionality lowers the T-c. No superconductivity was observed down to 4.3 K in (NH3)(y)Cs0.4FeSe at 11 and 13 GPa. Surprisingly, superconductivity re-appeared rapidly above 13 GPa, with the T-c reaching 49 K at 21 GPa. The appearance of a new superconducting phase is not accompanied by a structural transition, as evidenced by pressure-dependent XRD. Furthermore, T-c slowly decreased with increasing pressure above 21 GPa, and at 41 GPa superconductivity disappeared entirely at temperatures above 4.9 K. The observation of a double-dome superconducting phase may provide a hint for pursuing the superconducting coupling-mechanism of ammoniated/non-ammoniated metal-doped FeSe.

DOI： 10.1038/srep09477

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DOI： 10.1088/1742-6596/592/1/012013

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Other Link： http://stacks.iop.org/1742-6596/592/i=1/a=012013?key=crossref.52301fe8a7ab7dc86875a480b20bb037

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The pressure-temperature-field phase diagram and quantum fluctuation effect were investigated in the itinerant ferromagnet U3P4 by resistivity, ac susceptibility, and Hall effect measurements under high pressure. The zero-temperature ferromagnetic-to-paramagnetic transition is located at P-c similar to 4.0 GPa. The tricritical point exists at P* = 3.8 GPa and T* = 32 K, where the ferromagnetic transition changes from second- to first-order. As a quantum fluctuation effect, the low-temperature resistivity at P-c follows T-5/3 dependence, which was theoretically described in the case of a three-dimensional ferromagnet. This result indicates that the ferromagnetic-to-paramagnetic transition at P-c may be considered as weakly first-order. Another critical behavior, the huge enhancement of rho(0) observed at P-c, cannot be interpreted as the ferromagnetic fluctuation effect. The Hall effect measurements suggest that the magnetic structure in the ordered state changes under high pressure.

DOI： 10.7566/JPSJ.84.024705

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

We present detailed investigations on the effects of Ni substitution (x) on Ce(Cu1-xNix)(2)Si-2 with x < 0.3, and a pressure (p) study for x = 0.04(2), 0.05(2), and 0.09(2) by resistivity measurements. The Cu-Ni substitution suppresses both antiferromagnetic fluctuations and superconductivity in CeCu2Si2, and leads to a dramatic crossover from the heavy-fermion (HF) regime to the intermediate-valence(IV) regime with progressive Ni doping. The crossover can be characterized by a marked increase in Kondo temperature evaluated from resistivity, specific heat, and susceptibility measurements. In high-pressure resistivity measurements, the Ni-doped system exhibits similar anomalies to those observed in CeCu2Si2, namely, T-linear dependence, an enhancement of residual resistivity, and a marked decrease in the A coefficient of the T-2-resistivity. Furthermore, we observed an unexpected upturn anomaly in resistivity in the Ni-doped system under high pressure. By constructing the x-p phase diagram of Ce(Cu1-xNix)(2)Si-2, we demonstrate that the crossover from the HF regime to the IV regime can be associated with these characteristic anomalies in resistivity.

DOI： 10.7566/JPSJ.84.024702

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

We measured the pressure dependence of in-plane resistivity rho(ab) in the recently discovered iron-based superconductor Ca-10(Ir4As8)(Fe2-xIrxAs2)(5), which shows a unique structural phase transition in the absence of magnetic ordering, with a superconducting transition temperature T-c = 16 K and a structural phase transition temperature T-s similar or equal to 100 K at ambient pressure. T-c and T-s are suppressed on applying pressure and disappear at approximately 0.5 GPa, suggesting a relationship between superconductivity and structure. Ca-10(Ir4As8)(Fe2-xIrxAs2)(5) is a rather rare example in which the superconductivity appears only in a low-temperature ordered phase. The fact that the change in the crystal structure is directly linked with superconductivity suggests that the crystal structure as well as magnetism are important factors governing superconductivity in iron pnictides.

DOI： 10.1103/PhysRevB.90.224513

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DOI： 10.1103/PhysRevB.89.144509

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

DOI： 10.7566/JPSJ.83.015001

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Authorship：Lead author   Publishing type：Research paper (international conference proceedings)   Publisher：Journal of the Physical Society of Japan  

DOI： 10.7566/JPSCP.3.011081

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Publishing type：Research paper (international conference proceedings)  

DOI： 10.7566/JPSCP.3.015044

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

Alkali-metal-intercalated FeSe materials, (NH3) yM0.4FeSe (M: K, Rb, and Cs), have been synthesized using the liquid NH3 technique. (NH3)yCs 0.4FeSe shows a superconducting transition temperature (T c) as high as 31.2 K, which is higher by 3.8 K than the Tc of nonammoniated Cs0.4FeSe. The Tcs of (NH 3)yK0.4FeSe and (NH3) yRb0.4FeSe are almost the same as those of nonammoniated K0.4FeSe and Rb0.4FeSe. The Tc of (NH 3)yCs0.4FeSe shows a negative pressure dependence. A clear correlation between Tc and lattice constant c is found for ammoniated metal-intercalated FeSe materials, suggesting a correlation between Fermi-surface nesting and superconductivity. © 2013 American Physical Society.

DOI： 10.1103/PhysRevB.88.094521

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：KOREAN PHYSICAL SOC  

Zeolite LSX (low-silica X) crystals have an aluminosilicate framework with regular supercages and beta-cages. They are arrayed in a double diamond structure. The loading density of guest K atoms per supercage (or beta cage), n, can be controlled from 0 to a parts per thousand 9. At n &lt; 2, samples are nearly nonmagnetic and insulating. The Curie constant has a clear peak at n = 3, and the electrical resistivity suddenly decreases simultaneously. The electrical resistivity suddenly decreases again at n = 6 and shows metallic phase at n &gt; 6. These properties are explained by the polaron effect including the electron correlation. Ferrimagnetic properties are observed at n a parts per thousand 9. A remarkable increase in the resistivity is observed at very low temperatures at n a parts per thousand 9, and is discussed in terms of the hypothesis of a Kondo insulator.

DOI： 10.3938/jkps.63.512

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The longitudinal magnetoresistance (LMR) of polycrystalline Ce(Cu1-xNix)2Si2 samples is investigated between T = 2 and 15 K up to H = 80 kOe. The application of magnetic field induces anomalous temperature dependence of the resistivity with the power index n &lt
2 for x = 0.12 and 0.14, in which ρ(T) obeys a T 2-law at H = 0 Oe. A sign-change of the LMR from positive (x &lt
0.03) to negative (x &gt
0.03) is observed at 2 K. The negative LMR at 80 kOe is maximized (∼ -4 % at T = 2 K) around x ∼ 0.10 and subsequently disappears at higher Ni concentrations. Disappearance of the positive LMR in lower x region and the negative LMR at higher Ni concentrations implies a collapse of a coherent Kondo lattice state, and a rapid enhancement of Kondo temperature, respectively. Anomalous quantum fluctuations are probably developed around x ∼ 0.10. © 2013 The Korean Physical Society.

DOI： 10.3938/jkps.63.766

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：KOREAN PHYSICAL SOC  

Alkali metal nanoclusters can be stabilized in the regular cages of zeolite crystals by the loading of guest alkali metals. Cages are connected by the sharing of windows of the framework, and arrayed in simple cubic, diamond and body centered cubic structures in zeolites A, X and sodalite, respectively. The s-electrons have the localized nature of nanoclusters with magnetic moments, and have mutual interactions through the windows of cages. They show exotic magnetism depending on the structure type of zeolites, the kind of alkali metals and the average loading density of alkali atoms per cage. In zeolite A, potassium clusters are formed in α-cages that have an inside diameter of 11 Å. They exhibit ferromagnetic properties explained by the canted antiferromagnetism of the Mott insulator, where the 1p-like degenerate orbitals of clusters play an essential role in the magnetic properties. Na-K alloy clusters generated at supercages and β-cages of low-silica X (LSX) zeolite exhibit Néel's N-type ferrimagnetism at specific loading densities of alkali metals. Alkali metal clusters in sodalite show the ideal Heisenberg antiferromagnetism of the Mott insulator. © 2013 The Korean Physical Society.

DOI： 10.3938/jkps.63.699

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

Pressure effects on the rattling and superconductivity in the Einstein solids; A<inf>x</inf>V<inf>2</inf>Al<inf>20</inf>(A<inf>x</inf>= Ga<inf>0.2</inf>, Al<inf>0.3</inf>, and Y) are investigated by means of electrical resistivity measurements under high pressure. We observed bumps in resistivity at low temperatures only for Ga<inf>0.2</inf>and Al<inf>0.3</inf>, which can be explained by scattering of conduction electrons by local phonons with Einstein temperatures of 8.5 and 22 K, respectively. The bumps gradually fade out with increasing pressure, and the temperature variations of resistivity for Ga<inf>0.2</inf>and Al<inf>0.3</inf>approach those of Y. This indicates that the low-energy local phonons in the Ga and Al compounds disappear at high pressures. We also observed T^{2} behavior with large A coefficients in the low-temperature limit for Ga and Al compounds, but not for Y. With increasing pressure, the A coefficient is largely suppressed, while H_{\text{c2 } }' \equiv |\mathrm{d}H_{\text{c2 } }/\mathrm{d}T|_{T_{\text{c } } } that also reflects the density of states at Fermi energy decreases more slowly. The T^{2} behavior in Ga and Al compounds probably originates from el--ph scatterings enhanced by rattling of Ga and Al atoms rather than el--el scatterings. An enhancement in the superconducting transition temperatures by the rattling is also demonstrated by comparing the pressure responses of T_{\text{c } } between the three compounds. The enhancements of T_{\text{c } } and el--ph interaction \lambda is relatively small for these Einstein solids in contrast to those of the \beta-pyrochlore oxides.

DOI： 10.7566/JPSJ.82.063707

CiNii Article

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Publishing type：Research paper (scientific journal)  

The effects of Ni substitution on Ce(Cu1-xNix)2Si2 have been studied by
specific heat and electrical resistivity measurements. The specific heat
measurement has revealed that the enhanced quantum fluctuations around an
antiferromagnetic quantum critical point are markedly suppressed by Ni
substitution, and that the Fermi liquid state recovers in the Nirich region (x
> 0.12). The characteristic T-linear dependence of the resistivity has been
observed at approximately x ~ 0.10 together with a sign of superconductivity.
The variation of n in the form of rho - rho0 = aT^n against Tmax^1, at which
the resistivity peaks, coincides with the case of high-pressure experiments on
pure CeCu2Si2. The anomalous T-linear behavior appears to occur in the
crossover region from the Kondo regime to the valence fluctuation regime rather
than in the conventional antiferromagnetic quantum critical region.

DOI： 10.1143/JPSJ.81.083701

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

An overview of the crystal structures and physical properties of the recently discovered iron-platinum-arsenide superconductors, Ca-10(PtnAs8)(Fe2-xPtxAs2)(5) (n = 3 and 4), which have a superconducting transition temperature up to 38K, is provided. The crystal structure consists of superconducting Fe2As2 layers alternating with platinum-arsenic layers, PtnAs8. The upper critical field H-c2, hydrostatic pressure dependence of superconducting transition temperature T-c, and normal-state magnetic susceptibility are reported. (C) 2011 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ssc.2011.12.034

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/1742-6596/391/1/012005

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

We have measured Cu-63-NQR spectral lines and nuclear spin-lattice relaxation time T-1 under pressure up to 5.4 GPa. Daphne oil 7474 is used as the pressure-transmitting medium to obtain good hydrostaticity. NQR frequency (63)v(Q) above 4 GPa suddenly decreases from the linear pressure dependence in the low pressure range (P &lt;= 3.5 GPa). The observed sudden downward deviation of (63)v(Q) is associated with an increase of Ce valence. Above 4.5 GPa, the linear pressure dependence of (63)v(Q) is observed again, most likely related to the sharp crossover to the high valence state.

DOI： 10.1088/1742-6596/391/1/012012

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

Ca(Fe1-xRhx)(2)As-2 undergoes successive phase transitions with increasing Rh doping in the T = 0 limit. The antiferromagnetic-metal phase with orthorhombic structure at 0.00 &lt;= x &lt;= 0.020 is driven to a superconducting phase with uncollapsed-tetragonal (ucT) structure at 0.020 &lt;= x &lt;= 0.024; a non-superconducting collapsed-tetragonal (cT) phase takes over at x &gt;= 0.024. The breakdown of Fermi-liquid transport is observed in the ucT phase above T-c. In the adjacent cT phase, Fermi-liquid transport is restored along with a disappearance of superconductivity. This interplay of superconductivity and Fermi-liquid transport suggests the essential role of magnetic fluctuations in the emergence of superconductivity in doped CaFe2As2.

DOI： 10.1143/JPSJ.80.103701

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

Strain and resistivity measurements in UIr showed the occurrence of two structural phase transitions under high pressure, indicating the existence of three phases I-III, with slightly different crystal structures. It is suggested that ferromagnetic phases FM1-FM3 emerge in phases I-III, respectively. The pressure-temperature phase diagram was sensitive to the hydrostaticity of pressure. FM3 and superconductivity are observed in the measurements in which Daphne 7373 is used as a pressure-transmitting medium; however they are both absent in the case where petroleum ether is used as a pressure-transmitting medium. These results indicate a close relationship between ferromagnetism and superconductivity.

DOI： 10.1103/PhysRevB.84.054524

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Heat capacity and ac-susceptibility measurements under high pressure are carried out in SmOs4Sb12. Application of pressure increases the Curie temperature T-C and enhances the heat-capacity jump at T-C. On the other hand, the peak value of ac-susceptibility at T-C decreases above 1 GPa and then almost vanishes at 3.6 GPa. These experimental facts suggest that the ordered state in SmOs4Sb12 is not simple ferromagnetic state but possibly multipolar ordered state.

DOI： 10.1143/JPSJS.80SA.SA034

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We report the results of Hall effect measurements on CeCu2Si2 under high pressures up to 4.8 GPa. The Hall coefficient at ambient pressure increases with decreasing temperature and exhibits maximum at 4 K. The Hall coefficient at temperature higher than the coherent temperature of 10 K is consistent with the anomalous Hall effect. The pressure effect on the temperature dependence of the Hall coefficient is not simple. The pressure dependence of the Hall coefficient shows anomaly from 3.1 to 4.8 GPa, where the superconductivity is enhanced. These results indicate the close relationship between the Hall coefficient and the superconductivity.

DOI： 10.1143/JPSJS.80SA.SA061

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

Low-silica X (LSX) zeolite has the FAU-type framework structure constructed of supercages and beta-cages with effective inside diameters of 13 and 7 angstrom, respectively. Respective cages are arrayed in a diamond structure. Na-K clusters are formed by the loading of guest potassium atoms nK into LSX, where the unloaded LSX has 4Na and 8K zeolite-cations per supercage (or beta-cage) as given by Na(4)K(8)Al(12)Si(12)O(48). N-type ferrimagnetism has been observed at ambient loading densities of K atoms, 6.5 &lt; n &lt; 8.5. Ferrimagnetism was not observed at the maximum loading density at ambient pressure, n approximate to 9. In the present study, we extended the loading density for 9 &lt; n by the pressure-loading technique. Spontaneous magnetization is observed again below 10.5 and 9.1 K at the loading pressures approximate to 400 and approximate to 520 MPa respectively. Respective Weiss temperatures are -23 and -32 K. These results indicate that the ferrimagnetism appears again at higher loading densities.

DOI： 10.1088/1742-6596/200/1/012062

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

Potassium clusters arrayed in zeolite A are known to show ferromagnetic properties at low temperature. The origin of the spontaneous magnetization has been explained by a model of spin-canting in an antiferromagnetically ordered state. The direct information for the magnetic structure, however, has not been obtained so far. In the present work, we measure the neutron powder diffraction by using pulsed neutron source at KEK-KENS below and above the Curie temperature. No significant temperature-dependence was, however. obtained within the statistical errors, namely, magnetic scattering could not be detected separately. We also estimate the intensity of magnetic scattering by assuming some possible magnetic structures with considering the magnetic form factor of the cluster wave function. The intensity of magnetic scattering is estimated to be extremely weak and higher SIN of similar to 10(4) or more is required to detect the magnetic scattering of this material. (c) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nima.2008.11.038

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We studied systematically a series of the ternary compounds RRhIn5 (R: rare earth) which were grown in the single crystalline form by means of the flux method. Most of these compounds order antiferromagnetically at low temperatures, except for R = Y, La, Pr and Yb. The observed temperature dependence of the specific heat and the anisotropic features in the magnetic susceptibility and magnetization have been analyzed on the basis of the crystalline electric field (CEF) model, and an interesting relationship between the anisotropic exchange interaction and the CEF effect is obtained for RRhIn5 compounds. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2007.10.081

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We report on pressure-induced unconventional superconductivity (SC) in the heavy-fermion (HF) antiferromagnet CeIn3 by means of nuclear-quadrupole- resonance (NQR) studies conducted under a high pressure. The temperature (T) and pressure (P) dependences of the In-NQR spectra have revealed a first-order quantum-phase transition (QPT) from antiferromagnetism (AFM) to paramagnetism (PM) at a critical pressure Pc =2.46 GPa at which AFM disappears with a minimum value of TN (Pc) =1.2 K. High-energy x-ray scattering measurements under P show a progressive decrease in the lattice density without any change in the crystal structure, whereas an increase in the NQR frequency (νQ) indicates an increase in the hybridization between 4f electrons and conduction electrons, which stabilizes the HF-PM state. This competition between the AFM phase where TN is reduced and the formation of the HF-PM phase triggers the first-order QPT at Pc =2.46 GPa. Despite the lack of an AFM quantum critical point in the P-T phase diagram, we highlight the fact that unconventional SC occurs in both phases of AFM and PM. The measurements of the nuclear spin-lattice relaxation rate 1/T1 in the AFM phase have provided evidence for the uniformly coexisting AFM+SC phase. Remarkably, the significant increase in 1/T1 upon cooling in the AFM phase has revealed the development of low-lying magnetic excitations down to Tc in the AFM phase
it is indeed relevant to the onset of the uniformly coexisting AFM+SC phase. In the HF-PM phase where AFM fluctuations are not developed, 1/T1 decreases without the coherence peak just below Tc, followed by a power-law-like T dependence that indicates an unconventional SC with a line-node gap. Remarkably, Tc has a peak around Pc in the HF-PM phase as well as in the AFM phase. In other words, an SC dome exists with a maximum value of Tc =230 mK around Pc, indicating that the origin of the pressure-induced HF SC in CeIn3 is not relevant to AFM spin fluctuations but to the emergence of the first-order QPT in CeIn3. These phenomena observed in CeIn3 should be understood in terms of the first-order QPT because these new phases of matter are induced by applying P. When the AFM critical temperature is suppressed at the termination point of the first-order QPT, Pc =2.46 GPa, the diverging AFM spin-density fluctuations emerge at the critical point from AFM to PM. The results with CeIn3 leading to a new type of quantum criticality deserve further theoretical investigations. © 2008 The American Physical Society.

DOI： 10.1103/PhysRevB.77.064508

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We report on pressure-induced unconventional superconductivity (SC) in the heavy-fermion (HF) antiferromagnet CeIn3 by means of nuclear-quadrupole-resonance (NQR) studies conducted under a high pressure. The temperature (T) and pressure (P) dependences of the In-NQR spectra have revealed a first-order quantum-phase transition (QPT) from antiferromagnetism (AFM) to paramagnetism (PM) at a critical pressure P-c=2.46 GPa at which AFM disappears with a minimum value of T-N(P-c)=1.2 K. High-energy x-ray scattering measurements under P show a progressive decrease in the lattice density without any change in the crystal structure, whereas an increase in the NQR frequency (nu(Q)) indicates an increase in the hybridization between 4f electrons and conduction electrons, which stabilizes the HF-PM state. This competition between the AFM phase where T-N is reduced and the formation of the HF-PM phase triggers the first-order QPT at P-c=2.46 GPa. Despite the lack of an AFM quantum critical point in the P-T phase diagram, we highlight the fact that unconventional SC occurs in both phases of AFM and PM. The measurements of the nuclear spin-lattice relaxation rate 1/T-1 in the AFM phase have provided evidence for the uniformly coexisting AFM+SC phase. Remarkably, the significant increase in 1/T-1 upon cooling in the AFM phase has revealed the development of low-lying magnetic excitations down to T-c in the AFM phase; it is indeed relevant to the onset of the uniformly coexisting AFM+SC phase. In the HF-PM phase where AFM fluctuations are not developed, 1/T-1 decreases without the coherence peak just below T-c, followed by a power-law-like T dependence that indicates an unconventional SC with a line-node gap. Remarkably, T-c has a peak around P-c in the HF-PM phase as well as in the AFM phase. In other words, an SC dome exists with a maximum value of T-c=230 mK around P-c, indicating that the origin of the pressure-induced HF SC in CeIn3 is not relevant to AFM spin fluctuations but to the emergence of the first-order QPT in CeIn3. These phenomena observed in CeIn3 should be understood in terms of the first-order QPT because these new phases of matter are induced by applying P. When the AFM critical temperature is suppressed at the termination point of the first-order QPT, P-c=2.46 GPa, the diverging AFM spin-density fluctuations emerge at the critical point from AFM to PM. The results with CeIn3 leading to a new type of quantum criticality deserve further theoretical investigations.

DOI： 10.1103/PhysRevB.77.064508

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A series of ternary compounds RRhIn5 (R: rare earth) has been grown in the single crystalline form by means of the flux method. The magnetic properties of these compounds were investigated by measuring the lattice parameter, electrical resistivity, specific heat, magnetic susceptibility and magnetization. All the compounds crystallize in the tetragonal HoCoGa5-type structure. Most of these compounds order antiferromagnetically at low temperatures, except when R = Y, La, Pr, and Yb. The observed temperature dependence of the specific heat and the anisotropic features in the magnetic susceptibility and magnetization have been analyzed on the basis of the crystalline electric field (CEF) model. The overall energy splitting of the CEF scheme in RRhIn5 is estimated to be in the range from 44 to 330 K. The magnetic properties are discussed on the basis of the sign of the CEF parameter.

DOI： 10.1143/JPSJ.76.064702

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The pressure-doping technique was developed for further loading of guest potassium metal into porous crystals of zeolite beyond the upper limit at ambient pressure. A doping pressure dependence of the magnetic property of potassium clusters in cages of zeolite A is measured up to 320 MPa. The Curie constant monotonically decreases with increase in the doping pressure and shows very small values above 250 MPa. The magnetic susceptibility at 2 K, however, gradually increases and has a peak at 200 MPa. Observed decrease in the Curie constant is explained by the increase in the loading density of potassium. Simultaneously, the increase in the magnetic susceptibility at 2 K is explained by the superparamagnetism of ferromagnetic domains. A possible mechanism of change in the magnetic properties is discussed. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.220

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We studied the change of the Fermi surface properties in antiferromagnets CeIn3 and CeRhIn5 via the dHvA experiments under pressure. We found the abrupt change of the Fermi surface at the critical pressure P-c, where the magnetic ordering state changes to the paramagnetic one. The change of the Fermi surface indicates that the 4f-electron character is changed from localized to itinerant in CeIn3 and CeRhIn5 at P-c. Namely, the 4f-electron contributes to the volume of the Fermi surface above P-c. Interestingly, the pressure-induced heavy fermion state with large effective mass was observed around P-c, where the pressure-induced superconductivity appears. We also discuss the Fermi surface properties in the system without inversion symmetry in the crystal structure as in CePt3Si and CeTX3 (T:Co, Ir, Rh, X: Si, Ge). The spin-orbit interaction due to the lack of inversion symmetry brings about a splitting of the Fermi surface, which is important for considering the formation of Cooper pair. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.11.197

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We report the novel phase diagram of superconductivity (SC) and antiferromagnetism (AFM) in heavy-fermion (HF) pressure(P)-induced superconductors CeRhIn5 and CeIn5 through nuclear-quadrupole-resonance (NQR) measurements under P. The P-induced superconductivity in CeRhIn5 coexists with AFM on a microscopic level in P=1.5-1.9 GPa. By contrast, in CeIn3, the P-induced phase separation of AFM and paramagnetism (PM) takes place without any trace of a quantum phase transition. The outstanding finding is that SC sets in at both the phases magnetically separated into AFM and PM in P=2.28-2.5 GPa. © 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2005.10.043

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We grew single crystals of PrCoIn5, PrRhIn5, and PrIrIn5 with the tetragonal crystal structure and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization and de Haas-van Alphen effect. These Pr compounds reveal no magnetic ordering. The topology of the Fermi surfaces is the same as that of a non-4f reference compound LaRhIn5. The cyclotron mass and/or the electronic specific heat coefficient are also approximately the same as those of LaRhIn5. The magnetic susceptibility and magnetization are anisotropic, reflecting the crystal structure, which are well explained by the tetragonal crystalline electric field scheme with the singlet ground state. ©2005 The Physical Society of Japan.

DOI： 10.1143/JPSJ.74.3320

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We report the discovery of novel phases in CeIn3 on the verge of antiferromagnetism (AFM) through the In-nuclear quadrupole resonance (NQR) measurements. We have found that even though a pressure (P)-induced phase separation into AFM and paramagnetism (PM) takes place, a novel superconductivity (SC), which is induced without strong spin fluctuations, has been found to coexist with AFM on a microscopic level. We propose that the magnetic excitations such as spin-density fluctuations induced by the first-order magnetic phase transition might mediate attractive interaction to form Cooper pairs. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.01.083

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DOI： 10.1143/jpsj.73.1647

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Magnetic excitations in a single crystal of heavy-fermion superconductor PrOs4Sb12 have been studied by inelastic neutron scattering (INS) at low temperatures under high magnetic fields. The crystal field (CF) excitations at 0.7 meV observed in a previous INS study of a polycrystal sample were confirmed in this study on a single crystal. The observed excitations in the zero magnetic field soften around a wave vector $(1,0,0)$, which is the modulation vector of the field-induced antiferro-quadrupolar ordering, suggesting the presence of quadrupolar instability. The observed field dependence of excitations is better reproduced in a singlet ground-state model rather than in a non-Kramers doublet ground-state model. In a high resolution experiment, furthermore, the change of the excitation spectra at $(1,0,0)$ was observed on passing through the superconducting transition temperature, indicating that the excitation and the superconductivity are closely related in PrOs4Sb12.

DOI： 10.1143/JPSJ.73.1438

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Neutron scattering experiments have been performed to reveal the magnetic excitation in ferromagnet CeAgSb2: Crystalline electric field excitations were observed at 5.2 and 12.5 meV in the paramagnetic state. Our analysis concluded that vertical bar +/- 1/2) is the ground state. The observed ferromagnetic moment is in good agreement with the ground-state saturation moment, gJ mu(B)J(2) similar to 0.43 mu(B): The spontaneous moment along the c-axis decreases with increasing the field perpendicular to the c-axis, and disappear at the critical field H-c, where the magnetization curve shows the kink behavior. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.12.1258

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We found the field-induced antiferro-quadrupole (AFQ) ordering in the Pr-based heavy fermion superconductor PrOs4Sb12 by means of neutron scattering. The field-induced staggered moment and the field dependence of the crystal field excitation spectra can be well understood in terms of the mean field Hamiltonian based on the singlet Gamma(1) with triplet Gamma(4) first excited state, where the quadrupolar interaction plays essential role for the AFQ ordering. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.315

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DOI： 10.1088/0953-8984/15/28/307

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Systematic neutron-scattering experiments have been carried out in order to reveal the crystal and magnetic structures as well as the magnetic excitation in the Ce-based intermetallic compound CeAgSb2. It was clarified that the Ag atoms in CeAgSb2 (space group: P4/nmm) occupy the 2b site, while Sb atoms occupy 2a and 2c sites, which have, to date, been controversial in literature. From the analysis of neutron powder-diffraction profile, we found the existence of the ferromagnetic component of about 0.41mu(B)/Ce oriented along the c axis, consistent with the result of previous studies. On the other hand, however, no trace of the antiferromagnetic or spin-density wave peak was detected within our range of experimental accuracy. We observed a considerable spin-wave excitation below 3 meV. The dispersion relation was explained by the anisotropic Heisenberg model. This means that CeAgSb2 has a simple ferromagnetic structure. Furthermore, crystalline electric-field (CEF) excitations were observed at 5.2 and 12.5 meV in the paramagnetic state, which is indicative of the localized nature of the Ce-4f electron. Our analysis revealed that vertical bar J(z) = +/-1/2&gt; is the ground state, while the first and second excited levels are mainly due to vertical bar +/-3/2&gt; and vertical bar +/-1/2&gt;, respectively. The observed ferromagnetic moment is in good agreement with the ground-state saturation moment, g(J)mu(B)J(z)similar to 0.43mu(B). The susceptibility, magnetization curve, and magnetostriction can be explained in terms of the CEF level scheme with anisotropic exchange interaction. (C) 2003 The American Physical Society

DOI： 10.1103/PhysRevB.68.024408

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Neutron scattering experiments have been carried out that reveal the magnetic excitation in the ferromagnet CeAgSb2. Crystalline electric field excitations were observed at 5.2 and 12.5 meV in the paramagnetic state, indicative of the localized nature of the Ce 4f electron. Our analysis concluded that \J(z) = +/-(1)/(2)&gt; is the ground state, while the first and second excited levels are mainly due to \+/-(3)/(2)) and \+/-(5)/(2)&gt;, respectively. The observed ferromagnetic moment is in good agreement with the ground-state saturation moment, g(J)mu(B)J(z) similar to 0.43 mu(B). The spin wave dispersion is interpreted using the anisotropic Heisenberg model with ferromagnetic exchange interaction up to seventh-nearest neighbours. The spontaneous moment along the c-axis decreases with increasing field perpendicular to the c-axis, and disappears at the critical field H, which corresponds to the anomaly which appeared in the magnetization curve.

DOI： 10.1088/0953-8984/15/28/347

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Conference proceedings, Hanoi International Symposium on Magnetism

DOI： 10.1016/S0304-8853(03)00070-2

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Neutron diffraction experiments on the heavy-fermion superconductor PrOs4Sb12 revealed that a small antiferromagnetic moment, parallel to [010] ($y$-direction), is induced in the field-induced phase ($H \parallel z$). The analysis, based on the $\Gamma_{1}$ singlet ground state crystal field model, shows that antiferro-order of $O_{yz}$-type quadrupole moments of Pr ions is formed in the field-induced phase. This strongly suggests that the crystal field ground-state of Pr ions in PrOs4Sb12 is the $\Gamma_{1}$ singlet and the quadrupolar ordering is induced due to level crossing with an excited state under a magnetic field.

DOI： 10.1143/JPSJ.72.1002

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We have studied the de Haas-van Alphen (dHvA) effect under pressure for an antiferromagnet CeRhIn5, where the antiferromagnetic state is changed into the superconducting state at higher pressures than 1.6 GPa. It is clarified from the present dHvA experiment that the topology of the Fermi surface is unchanged up to 2.1 GPa but the cyclotron mass increases strongly above 1.6 GPa. Superconductivity is found to be realized in this heavy fermion state. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02366-9

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We report evidences for bulk nature and unconventional superconductivity in CeIn3 at P = 2.65 GPa revealed by the measurements of nuclear-spin-lattice-relaxation time (T-1) and ac-susceptibility (ac-chi). Both the measurements of ac-chi and T, have pointed to a superconducting transition at T = 95 mK, which is very much lower than an onset temperature T-onset = 0.15 K at zero resistance. The temperature dependence of 1/T-1 shows no coherence peak just below T-c, indicative of an unconventional nature for the superconductivity. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(02)02732-6

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DOI： 10.1080/00223131.2002.10875416

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We report evidence for unconventional superconductivity in CeIn3 at a pressure P=2.65 GPa above the critical pressure (Pc∼2.5 GPa) revealed by measurements of the nuclear-spin-lattice-relaxation time (T1) and ac susceptibility (ac-x). Both measurements of T1 and ac-x have pointed to a superconducting transition at Tc=95 mK, which is much lower than the onset temperature Tonset=0.15 K at zero resistance. The temperature dependence of 1/T1 shows no coherence peak just below Tc, indicative of an unconventional nature for the superconductivity induced in CeIn3.

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We report evidence for unconventional superconductivity in CeIn3 at a pressure P=2.65 GPa above the critical pressure (P(c)similar to2.5 GPa) revealed by measurements of the nuclear-spin-lattice-relaxation time (T-1) and ac susceptibility (ac-chi). Both measurements of T-1 and ac-chi have pointed to a superconducting transition at T-c=95 mK, which is much lower than the onset temperature T-onset=0.15 K at zero resistance. The temperature dependence of 1/T-1 shows no coherence peak just below T-c, indicative of an unconventional nature for the superconductivity induced in CeIn3.

DOI： 10.1103/PhysRevB.66.054521

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We observed de Haas-van Alphen (dHvA) oscillations in CeRh2Si2 at 1.3 GPa, higher than the quantum critical pressure p(c)similar or equal to1.0 GPa. Three observed dHvA branches correspond to the result of the 4f-itinerant model. Their cyclotron masses are large, being 24m(0), 29m(0) and 31m(0), about 4 times larger than the corresponding band masses. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(01)01359-X

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We have performed the de Haas-van Alphen (dHvA) and ac-susceptibility experiments on a ferromagnet UGe2 under pressure for the field along the easy a-axis. The p-H phase diagram was determined, indicating three kinds of phase: paramagnetic and weakly and strongly polarized phases. The detected dHvA frequencies as well as the cyclotron masses are found to be very different between the weakly and strongly polarized states. A change of the Fermi surface occurs when the weakly polarized phase is changed into the strongly polarized phase with increasing magnetic field.

DOI： 10.1088/0953-8984/14/5/103

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We carried out the de Haas-van Alphen (dHvA) experiment under pressure for a ferromagnet UGe2. The dHvA frequency of a main dHvA branch named α, that corresponds to a majority up-spin band 40-hole Fermi surface, decreases monotonously with increasing pressure, but in the pressure range from P*c (≃1.2 GPa) to pc (≃1.5 GPa) the dHvA signal disappears completely, where pc and p*c correspond to critical pressures for a Curie temperature TC and the second phase transition temperature T* (&lt
TC), respectively. For p &gt
pc we observed new dHvA branches with large cyclotron masses of 19-64m0, which correspond to main Fermi surfaces in the paramagnetic state.

DOI： 10.1088/0953-8984/14/1/104

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We observed the de Haas–van Alphen (dHvA) oscillations in CeRh₂Si₂under pressures up to 1.54 GPa. Three dHvA branches at higher pressure than the critical pressure <italic>p</italic>_c≃1.06 GPa are well explained by the result of the 4<italic>f</italic>-itinerant model. Their cyclotron masses are large, being 24<italic>m</italic>₀, 30<italic>m</italic>₀and 31<italic>m</italic>₀, which are about 4 times larger than the corresponding band masses.

DOI： 10.1143/JPSJS.71S.273

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We report the pressure (P)-temperature (T) phase diagram of antiferromagnetism and superconductivity in CeRhIn5 and CeIn3 revealed by the 115In nuclear-spin-lattice-relaxation (T1) measurement. In the itinerant magnet CeRhIn5, we found that the Néel temperature TN is reduced at P ≥ 1.23 GPa with an emergent pseudogap behavior. In CeIn3, the localized magnetic character is robust against the application of pressure up to P ∼ 1.9 GPa, beyond which the system evolves into an itinerant regime in which the resistive superconducting phase emerges. We discuss the relationship between the phase diagram and the magnetic fluctuations.

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We have studied Fermi surface properties of LaRhIn5 and CeTIn5 (T: Co, Rh and Ir) via the de Haas-van Alphen (dlivA) experiment. These Fermi surfaces are nearly cylindrhnal, reflecting the unique tetragonal crystal structure. The cyclotron mass or the gamma value is found to be strongly field-dependent in CeCoIn5. We have also carried out the dIlvA experiment under pressure for CeRhIn5.

DOI： 10.1143/JPSJS.71S.276

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DOI： 10.1088/0953-8984/14/21/102

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DOI： 10.1016/S0022-3697(02)00156-7

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DOI： 10.1103/PhysRevB.66.214510

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We report evidence for unconventional superconductivity in (formula presented) at a pressure (formula presented) above the critical pressure (formula presented) revealed by measurements of the nuclear-spin-lattice-relaxation time (formula presented) and ac susceptibility (ac- (formula presented) Both measurements of (formula presented) and ac- (formula presented) have pointed to a superconducting transition at (formula presented) which is much lower than the onset temperature (formula presented) at zero resistance. The temperature dependence of (formula presented) shows no coherence peak just below (formula presented) indicative of an unconventional nature for the superconductivity induced in (formula presented). © 2002 The American Physical Society.

DOI： 10.1103/PhysRevB.66.054521

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We report the pressure (formula presented)-temperature (formula presented) phase diagram of antiferromagnetism and superconductivity in (formula presented) and (formula presented) revealed by the (formula presented) nuclear-spin-lattice-relaxation (formula presented) measurement. In the itinerant magnet (formula presented) we found that the Néel temperature (formula presented) is reduced at (formula presented) with an emergent pseudogap behavior. In (formula presented) the localized magnetic character is robust against the application of pressure up to (formula presented) beyond which the system evolves into an itinerant regime in which the resistive superconducting phase emerges. We discuss the relationship between the phase diagram and the magnetic fluctuations. © 2001 The American Physical Society.

DOI： 10.1103/PhysRevB.65.020504

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DOI： 10.1143/JPSJS.71S.282

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Evolution of the pressure-induced heavy fermion state and superconductivity in (formula presented) have been established by high-pressure Fermi surface studies using dHvA technique. The effective mass of the conduction electrons named branch (formula presented) increases from 5.5 (formula presented) at ambient pressure to 20 (formula presented) at 1.6 GPa where superconductivity sets in. This heavy electron mass continues to increase steeply up to 2.1 GPa, 45 (formula presented) at 2.1 GPa, with a concomitant increase of the superconducting transition temperature. However, the underlying Fermi surface remains approximately same even at 2.1 GPa, strongly suggesting that antiferromagnetic fluctuations of Ce moments do not contribute to the volume of the Fermi surface, but enhance the cyclotron mass of the conduction electrons. © 2002 The American Physical Society.

DOI： 10.1103/PhysRevB.66.214510

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That the 4f electrons in the rare-earth antiferromagnetic compound CeRh2Si2 should be considered as localized electrons at cerium sites has been confirmed by comparing a de Haas-van Alphen experiment to the result of energy band calculations for LaRh2Si2. When pressure p is applied to the compound, the Neel temperature T-N1 = 36 K decreases and finally becomes zero at p(c)similar or equal to1.0-1.1 GPa. The topology of the Fermi surface is found to be almost unchanged up to 1.0 GPa, but the cyclotron effective mass increases with increasing pressure. Above 1.1 GPa, the topology of the Fermi surface changes abruptly. A new Fermi surface is explained by the 4f-itinerant-band model. The corresponding cyclotron mass is large, being about 22m(o).

DOI： 10.1103/PhysRevB.64.224417

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We succeeded in growing a high-quality single crystal of CeRh2Si2 with a residual resistivity ratio of 110. Under a pressure of 1.1 GPa, superconductivity is found below T-c = 0.38 K. where a Neel temperature of T-N = 36 K is suppressed down to almost zero. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(00)00785-X

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We have studied the pressure dependence of the specific heat in a CeNi single crystal using a clamp-type pressure-cell up to 0.8 GPa. The pressure dependence of the electronic specific heat coefficient is found to exhibit a sharp drop at 0.3–0.4 GPa. The present result indicates the instability of a mixed valence state of 4f electrons.

DOI： 10.1143/JPSJ.70.753

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We measured the specific heat, thermal expansion coefficient, magnetization, electrical resistivity, magnetoresistance and de Haas-van Alphen (dHvA) effect in PrSn3. The dense Kondo effect was confirmed from a negative magnetoresistance and the presence of heavy electrons with the cyclotron effective mass of 8-9mo for the main Fermi surface. A magnetic anisotropy was found below TN, having an easy axis of 〈1 1 0〉. © 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(00)00628-4

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We measured the specific heat, thermal expansion coefficient; magnetization, electrical resistivity, magnetoresistance and de Haas-van Alphen (dHvA) effect in PrSn3. The dense Kondo effect was confirmed from a negative magnetoresistance and the presence of heavy electrons with the cyclotron effective mass of 8-9 m(0) for the main Fermi surface. The magnetic phase diagram was also clarified by the high-field magnetization measurement.

DOI： 10.1143/JPSJ.69.3983

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We have measured the AC magnetic susceptibility of single crystals of the heavy fermion compounds CeCu6 and CeNi at temperatures down to 250 mu K. The susceptibility of CeCu6 shows a peak at about 2 mK in a zero magnetic field. The peak height along a-axis is about 10 times as large as along b- and c-axis, and decreases to zero in increasing field up to 11 mT. It is likely that the susceptibility of CeNi along c-axis has three peaks: below 350 mu K, at 47 mK and at 0.3 K, respectively. The two peaks at lower temperatures are suppressed by a magnetic field. The newly observed peaks in the susceptibilities for CeCu6 and CeNi suggest effects of magnetic impurities rather than of magnetic ordering. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(99)02533-8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Science Publishers B.V.  

An intermediate valence compound CeNi exhibits a phase transition under pressure, which is associated with the γ-α transition in Ce. To clarify a change of the electronic state under pressure, we measured the de Haas-van Alphen (dHvA) effect under pressure up to 6 kbar using a Cu-Be pressure cell. The dHvA branches are still observed after the phase transition. The topology of the Fermi surface is therefore unchanged. The cyclotron effective mass is, however, reduced from 11 to 3.2 m0 for branch ε and from 5.4 to 1.2 m0 for branch σ when the pressure is changed from 1 bar to 3.7 kbar.

DOI： 10.1016/S0921-4526(99)00844-3

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We measured the electrical resistivity, magnetoresistance and de Haas-van Alphen effect in PrSn3. The Kondo effect was confirmed from a negative magnetoresistance and the presence of heavy electrons with the cyclotron effective mass m(c)* = 7.33-9.3 m(0). (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/s0921-4526(99)00813-3

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In order to investigate the 5f electronic properties in a ferromagnet UGa2 with the hexagonal structure, we have performed the magnetic, elastic, transport and de Haas-van Alphen experiments. From these properties, the crystal distortion is found to occur below 100 K in the basal plane, which is most likely driven by the development of a ferromagnetic moment oriented along the [1 1 (2) over bar 0] direction. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(99)01114-X

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

We have measured the ac magnetic susceptibility in various fields and thermal expansion of single crystals of the heavy fermion compound CeCu6 at temperatures down to 250 mu K. The susceptibility of CeCu6 shows a peak at about 2 mK and has a large anisotropy. We also detected an anomaly of thermal expansion at the same temperature. The observed behaviors of the susceptibility and the thermal expansion in CeCu6 indicate the occurrence of an antiferromagnetic order.

DOI： 10.1103/PhysRevLett.84.5407

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DOI： 10.1016/S0921-4526(99)00930-8

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A self-consistent band calculation including an orbital polarization is performed for ferromagnetic UGa2 on the basis of an all-electron fully-relativistic spin-polarized LAPW (RSPLAPW) method with exchange-correlation potentials in a local density approximation (LDA). The obtained magnetic moment is composed of the spin of about - 2.0 mu(B) and the orbital moment of about 4.9 mu(B). Accordingly, it can be interpreted as if the configuration were a localized 5f(2), though the f character contains about 2.5 as valence electrons. From the band structure, the Fermi surface is constructed in order to analyze frequencies observed by the de Haas-van Alphen (dHvA) effect. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(99)01217-X

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

We have studied the magnetic and Fermi surface properties in a ferromagnet UGa2.The electrical resistivity, elastic constant, thermal expansion coefficient, thermoelectric power, magnetic susceptibility and Hall coefficient indicate highly anisotropic properties, reflecting the hexagonal structure.The 5f2- and 5f3-CEF schemes, based on the localized 5f-electron nature, are discussed to understand the magnetic susceptibility and magnetization data.We have also done the magnetoresistance and de Haas-van Alphen (dHvA) experiments to investigate the Fermi surface properties.Both data are very complicated, implying that the Fermi surface is a multiply-connected one.They are explained neither by the localized 5f2- and 5f3-core models nor by the spin-polarized 5f-itinerant model. The cyclotron mass is, however, rather light, ranging from 0.17 to 6.2 m0,which is consistent with the electronic specific heat coefficient of 11 mJ/K2&middot;mol.

DOI： 10.1143/JPSJ.69.2647

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High-field magnetization measurements in a heavy fermion antiferromagnet CeRh2Si2 were performed under high pressures at various temperatures to study the nature of the metamagnetism. Metamagnetic transitions were observed not only in the antiferromagnetic state but also in the paramagnetic state at various pressures. The metamagnetism in CeRh2Si2 does not originate from the rearrangement of antiferromagnetic moments but from the recovery of the local moment from the Kondo singlet state by applying high magnetic fields.

DOI： 10.1016/S0921-4526(99)00973-4

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DOI： 10.11316/jpsgaiyo.55.1.3.0_504_3

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Angular dependence of the transverse magnetoresistance of a heavy-fermion superconductor UBe13 (T-c = 0.9 K) was measured on a single crystal grown by the Al-flux method. The resistivity decreases with increasing the magnetic field at low temperatures, indicating that a magnetic scattering is suppressed by the magnetic field. We observed a remarkable angular dependence in magnetoresistance at 0.45 K under a constant held of 13 T, showing a minimum at the [1 1 0] direction. This anisotropy of magnetoresistance is observed below 4 K. Since the large resistivity (200 mu Ohm cm) of this compound at low temperatures is attributed to the magnetic scattering by uranium ions, the present anisotropy in the magnetic scattering at low temperatures would give important information about the ground state of 5f electrons. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(98)00948-X

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan (JPS)  

We have carried out the de Haas-van Alphen (dHvA) experiments in a valence fluctuating compound CeNi.Forty seven dHvA branches are observed experimentally, which are mainly centered at the symmetrical axes.Most of the dHvA branches are approximately explained by the 4f-itinerant band model.The cyclotron mass is in the range from 3.0 to 27 m0.Branch α, which has the largest cross-sectional area of the Fermi surface in the detected branches along the a-axis, has the cyclotron mass of 27 m0.This mass is five times larger than the corresponding band mass of 5.45 m0.

DOI： 10.1143/JPSJ.68.3334

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DOI： 10.1016/S0921-4526(98)00909-0

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DOI： 10.11316/jpsgaiyo.54.2.3.0_537_2

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We have grown single crystals of CeRh2Si2 and LaRh2Si2, and measured the temperature dependence of the thermal expansion coefficient.The magnetic component of the thermal coefficient in CeRh2Si2 hasbeen analyzed on the basis of the crystalline electric field.We have also succeeded in observing the de Haas-van Alphen (dHvA) effect ofCeRh2Si2.The detected dHvA branches are small in cross-section and are observed in anarrow angle region centered at the symmetrical axis, reflecting themultiply-connected Fermi surface.

DOI： 10.1143/JPSJ.67.2915

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

DOI： 10.1143/JPSJ.67.2553

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We have studied the origin of the cooperative Jahn-Teller effect and the metamagnetic transition in the orthorhombic compound PrCu2. We have determined the anisotropic ferroquadrupole phase diagram by measuring the specific heat and thermal expansion under magnetic fields. With increasing the field, the Jahn-Teller transition temperature increases slightly for the field along a-and c-axes, while It decreases intensively along the b-axis. The phase diagram can he explained quantitatively by including the quadrupolar interaction of -K-JT (O-xy) O-xy in the crystalline electric field and Zeeman Hamiltonian. The metamagnetic transition, which brings about the conversion between the easy (a)- and hard (c)-axes magnetization, has been also studied through the magnetostriction. This phenomenon is also explained quantitatively on the basis of the quadrupolar interaction of -K-M (O-2(2)) O-2(2). The sign of (O-2(2)) is found to be negative in the state where the c-axis is the hard one, while it changes from negative to positive above the metamagnetic transition field.

DOI： 10.1143/JPSJ.67.636

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We have studied the origin of the cooperative Jahn-Teller effect in PrCu2. We have determined the anisotropic phase diagram by measuring the thermal expansion and the magnetostriction in magnetic fields up to 15 T. The Jahn-Teller transition temperature is almost constant for the field along the a- and c-axis, while it decreases with increasing the field along the b-axis. The phase diagram can be explained qualitatively by including the quadrupolar interaction for [0(xy)] in the crystalline electric field Hamiltonian. (C) 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(97)00500-3

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DOI： 10.1016/s0921-4526(96)00834-4

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We have grown single crystals of CeRh2Si2 and LaRh2Si2 by the Czochralski pulling method in a tetra-arc furnace. The electrical resistivity and magnetic susceptibility are highly anisotropic, reflecting the tetragonal crystal structure. A metamagnetic transition is found for the magnetic field along the [001] direction at 26 T. © 1997, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.66.2260

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Language：Japanese   Publisher：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.71.1.0_2434

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DOI： 10.11316/jpsgaiyo.71.2.0_1977

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DOI： 10.11316/jpsgaiyo.71.1.0_2427

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DOI： 10.11316/jpsgaiyo.69.1.3.0_561_4

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DOI： 10.11316/jpsgaiyo.68.2.3.0_587_2

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Language：Japanese   Publisher：Japan Society of High Pressure Science and Technology  

In this article, we have developed pressure loading technique to extend the loading density of guest alkali metals in nanoporous crystals of zeolites. Zeolite crystals have solid framework and open regular nanospace. In the nanocages of zeolite crystals, s-electrons provided by the guest alkali metals occupy quantum electronic states of clusters successively. Under the pressure by the use of the pressure medium of alkali metals, we have observed significant change in the magnetic properties, indicating that the pressure loading increases loading densities which are closely related to the s-electron occupation at the quantum states of clusters.

DOI： 10.4131/jshpreview.22.44

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