Jiro Kitagawa

Low-temperature magnetic properties of (RE)3Pd20Si6 (RE=La to Yb)

Abstract We have investigated the magnetic and transport properties of (RE) 3 Pd 20 Si 6 (RE= La to Yb) by measuring the magnetic susceptibility, electrical resistivity and specific heat, All rare-earth (RE) ions in these compounds are in the trivalent state and magnetically order at low temperatures except RE= La and Eu. The compounds of Nd, Sm, Gd, Tb, Dy and Ho exhibit two magnetic phase transitions, Both higher and lower ordering temperatures generally follow the de Gennes scaling, Mean-field theory for the RKKY interaction indicates a relatively small exchange constant of about 30 meV·atom for these compounds, The compounds of Ce, Pr, Er, Tm and Yb show only one magnetic phase transition and deviate from the de Gennes scaling, Ce 3 Pd 20 Si 6 is a Kondo-lattice compound with a low ordering temperature as reported earlier, The (RE) 3 Pd 20 Si 6 compounds have a small energy splitting due to the crystal line-electfic-field (CEF) effect, probably because of the large coordination number around the RE ions, The de Gennes scaling in this series of compounds is discussed as a result of the interplay between the CEF interaction and the RKKY interaction.

New heavy-electron system Ce3Pd20Si6

Magnetic and transport properties of the ternary compound Ce 3 Pd 20 Si 6 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 · K 2 at 0.2 K. This leads to the conclusion that Ce 3 Pd 20 Si 6 is one of the heaviest-electron systems.

Suppression of antiferromagnetism by Kondo effect and quantum critical behavior in CeCoGe3-xSix (0≤ x< 3)

Several pseudoternary compounds of the CeCoGe 3- x Si x system were studied by magnetic-susceptibility, electrical-resistivity and specific-heat measurements. Substitution of silicon for germanium generates the normal chemical pressure and enhances the exchange interaction. The antiferromagnetism in CeCoGe 3 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.

Low-Temperature Magnetic Properties of Several Compounds in Ce-Pd-X (X=Si,Ge and Al) Ternary Systems

We have investigated several ternary compounds of cerium in the Ce-Pd-X (X=Si, Ge and Al) systems and their La counterparts by measuring the magnetic susceptibility, electrical resistivity and specific heat. The Ce ions in these compounds are in the nearly trivalent state and most of them show magnetic order of either long-range or spin-glass type at low temperatures. None of them distinctly exhibits the heavy fermion behavior, although it may be obscured by atomic disorder in some compounds. The relation between several isostructural ternary compounds of Ce-Pd-(Si and Ge) or Ce-Pd-(Al and Ga) system is qualitatively discussed in the framework of the Doniach phase diagram. The variation of the unit cell volume suggests that the former group is consistent with this phase diagram but the latter is not seemingly so. We found that LaPdSi 3 and LaPd 0.6 Ge 1.4 among the La counterparts are superconducting below 2.6 and 2.8 K, respectively.

Heavy-Electron Behavior in CePd3.8Al7.2

We have found a new compound CePd 3.8 Al 7.2 which crystallizes in the tetragonal BaCd 11 -type structure. We report the results of the low-temperature specific heat and magnetic susceptibility measurements. The compound did not exhibit any long-range magnetic order down to about 0.5 K. The value of specific heat divided by temperature is strongly enhanced and reaches 6 J/mole· K 2 at the lowest temperature. This confirms that CePd 3.8 Al 7.2 is one of the heaviest electron systems.

Anisotropic magnetic phase diagram of Ce3Pd20Ge6 with quadrupolar ordering

We have constructed the magnetic phase diagram of Ce3Pd20Ge6 up to 4 T by measuring the specific heat and the electrical resistivity in magnetic fields applied along three principal directions, which suggests the existence of a highly anisotropic interaction between the electric quadrupolar moments and the magnetic dipolar moments.

Low-temperature specific heat of Ce3−xLaxPd20Si6

We present the results of the low-temperature specific heat of Kondo compound Ce3-xLaxPd2oSi6 (x =0, 1, 2 and 2.7) and its magnetic-field dependence for x =0. The magnetic part of specific heat divided by temperature, C~/T, for x =0 makes a peak as high as 9 J/mol Ce K 2 at 0.2 K. On the other hand, Cm/T for the other xs keeps increasing monotonically below 0.2 K and the Fermi-liquid ground state is not realized even in diluted samples. It was found that the magnetic field strongly depresses Cm/T at low temperatures.

μ+SR Study of Ordering Phenomena in the Heavy-Fermion State of Ce3Pd20Ge6

Magnetic and quadrupolar ordering phenomena in a Ce3Pd20Ge6 single crystal have been investigated by muon spin rotation/relaxation (μ+SR) spectroscopy. We have observed spontaneous precession of muons in zero-field below TN=0.7 K in the antiferromagnetic state. The precession frequency follows the power law: ν(T)=ν(0)(1−T/TN)n. The exponent n=0.43(2) is close to the mean-field value of 0.5. The muon longitudinal spin relaxation rate 1/T1 is found to be nearly independent of temperature in the range of 0.3 to 2 K, i.e., across either TN or TQ=1.2 K, the quadrupolar ordering temperature. Two likely mechanisms for the temperature independent behavior of 1/T1 are suggested.