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We review recent investigations of the heavy-fermion antiferromagnet Ce7Ni3with a geometrically frustrated structure under hydrostatic pressures and magnetic fields. BelowTN1=1.9 K, an incommensurate spin-density-wave (SDW) develops, and another antiferromagnetic transition occurs atTN2 = 0.7 K. At a rather low critical pressure (Pc),Pc = 0.39 GPa, bothTN1andTN2vanish, and the specific heat divided by temperature (C/T) exhibits –lnTdependence (i.e., non-Fermi liquid behavior). AtP = 0.43 GPa > Pc, aT-independent behavior ofC/T, i.e., Fermi-liquid behavior, recovers below 0.2 K. However, the magnetic susceptibility continues to increase down to 0.09 K at 0.43 GPa, which is not consistent with a conventional Fermi-liquid theory. On the other hand, upon applying magnetic fieldsBalong the hexagonalcaxis,TN1decreases and vanishes at 0.3 T. Magnetoresistance, specific-heat, and magnetization measurements reveal that a field-induced magnetic (FIM) phase appears in aB–Tregion forB∥c > 0.7 T andT < 0.5 K. Neutron diffraction experiments indicate that the magnetic unit cell in thecplane for the FIM phase is treble that of the chemical unit cell. Moreover, the intensity of the magnetic reflection remains even in the region between the FIM phase and SDW phase. This observation indicates the presence of large spin fluctuations in thec-plane associated with the magnetic frustration, which should be responsible for the non-Fermi-liquid behavior of Ce7Ni3. [ABSTRACT FROM AUTHOR]

We review recent investigations of the heavy-fermion antiferromagnet Ce7Ni3with a geometrically frustrated structure under hydrostatic pressures and magnetic fields. BelowTN1=1.9 K, an incommensurate spin-density-wave (SDW) develops, and another antiferromagnetic transition occurs atTN2 = 0.7 K. At a rather low critical pressure (Pc),Pc = 0.39 GPa, bothTN1andTN2vanish, and the specific heat divided by temperature (C/T) exhibits –lnTdependence (i.e., non-Fermi liquid behavior). AtP = 0.43 GPa > Pc, aT-independent behavior ofC/T, i.e., Fermi-liquid behavior, recovers below 0.2 K. However, the magnetic susceptibility continues to increase down to 0.09 K at 0.43 GPa, which is not consistent with a conventional Fermi-liquid theory. On the other hand, upon applying magnetic fieldsBalong the hexagonalcaxis,TN1decreases and vanishes at 0.3 T. Magnetoresistance, specific-heat, and magnetization measurements reveal that a field-induced magnetic (FIM) phase appears in aB–Tregion forB∥c > 0.7 T andT < 0.5 K. Neutron diffraction experiments indicate that the magnetic unit cell in thecplane for the FIM phase is treble that of the chemical unit cell. Moreover, the intensity of the magnetic reflection remains even in the region between the FIM phase and SDW phase. This observation indicates the presence of large spin fluctuations in thec-plane associated with the magnetic frustration, which should be responsible for the non-Fermi-liquid behavior of Ce7Ni3. [ABSTRACT FROM AUTHOR]

The one-dimensional coordination polymers {[Cu II (hfac) 2 ] 3 ( m -BNN)} n · n CH 2 Cl 2 (1 ·CH 2 Cl 2 , P 1̄) and {[Cu II (hfac) 2 ] 3 ( m -BNN)} n (1', P 2/ n ), hfac = hexafluoroacetylacetonate and m -BNN = meta -phenylene bis(nitronyl-nitroxide), were obtained from CH 2 is transformed to 1 at 335 K. Their magnetic susceptibilities differ in both magnitude and temperature dependence behavior. 1 and 1' undergo a ferroelastic-like phase transition at 110 K and an unidentified one at 37 K. There is a subtle long relaxation of this ferroelastic-like ordered state.2 and CHCl 3 , respectively. 1 ·CH 2 Cl 2 is transformed to 1 at 335 K. Their magnetic susceptibilities differ in both magnitude and temperature dependence behavior. 1 and 1' undergo a ferroelastic-like phase transition at 110 K and an unidentified one at 37 K. There is a subtle long relaxation of this ferroelastic-like ordered state.

The crystalline electric field (CEF) level scheme and magnetic structure of a tetragonal antiferromagnet CePd 5 Al 2 with [Formula: see text] K and [Formula: see text] K were studied by neutron scattering, magnetization and magnetoresistance measurements. Inelastic neutron scattering measurements on the powder sample revealed CEF excitations at 21.3 and 22.4 meV. The derived wave functions of the CEF ground state for the Ce 3+ ion consist primarily of [Formula: see text] under the tetragonal symmetry. By means of single-crystal neutron diffraction, magnetic Bragg peaks characterized by a propagation vector [Formula: see text] were observed at [Formula: see text]. Our analysis indicates a sinusoidally modulated magnetic structure with amplitude of 2.0(1) [Formula: see text]/Ce, where the magnetic moments point to the [Formula: see text]-axis. The intensity of the third-order harmonic at 0.8 K is 1/30 as small as that expected for an antiphase structure, suggesting that the modulated structure remains at least down to 0.8 K. Both the magnetization and magnetoresistance show several anomalies in the magnetically ordered phase, indicating field-induced successive changes of the magnetic structure.

Electrical resistivity ρ(T) and specific heat C(T) measurements have been made on the diluted 4f^{2} system Y(Pr)Ir&#95;{2}Zn&#95;{20}. Both data of ρ and magnetic specific heat C&#95;{m} per Pr ion are well scaled as a function of T/T&#95;{0}, where T&#95;{0} is a characteristic temperature of non-Fermi-liquid (NFL) behaviors. Furthermore, the temperature dependences of ρ and C&#95;{m}/T agree with the NFL behaviors predicted by the two-channel Kondo model for the strong coupling limit. Therefore, we infer that the observed NFL behaviors result from the single-site quadrupole Kondo effect due to the hybridization of the 4f^{2} states with multichannel conduction electrons.

A developed alternating current calorimeter for measuring the absolute value of specific heat C of a very small sample under a pressure up to 10 GPa and low temperature below 10 K is described. A Bridgman anvil cell made of tungsten carbide with a top diameter of 3 mm is used. A hollow at the top prevents expansion of the sample space over the anvil top. Two chip resistors, which act as a thermometer and a heater, are mounted on the outer part of a copper-beryllium gasket with a frying pan-like shape. Thus, the thermometer is not pressurized. In order to isolate the gasket from the anvil thermally, diamond powder with a grain size of 0.25 μm is placed on the anvil top. Two jumps of C at the superconducting transitions of Pb (3.3 mg) and In (5.0 mg) are observed under various pressures up to 9 GPa, as clearly as those at the ambient pressure.

We performed electrical resistivity ρ, magnetic susceptibility χ, specific heat C and electron diffraction measurements on single-crystalline samples of PrT2Zn20 (T = Ru, Rh and Ir). The three compounds show the Van Vleck paramagnetic behavior, indicating the nonmagnetic crystalline electric field (CEF) ground states. A Schottky-type peak appears at around 14 K, irrespective of the T element, which can be moderately reproduced by a doublet–triplet model. For T = Ru, a structural transition occurs at Ts = 138 K, below which no phase transition appears down to 0.04 K. On the other hand, for T = Ir, antiferroquadrupole (AFQ) ordering arising from the nonmagnetic Γ3 doublet takes place at TQ = 0.11 K. For T = Rh, despite a structural transition between 170 and 470 K, the CEF ground state is still the non-Kramers Γ3 doublet. However, no phase transition due to the Γ3 doublet was observed even down to 0.1 K.

An antiferroquadrupolar ordering at T(Q)=0.11  K has been found in a Pr-based superconductor PrIr(2)Zn(20). The measurements of specific heat and magnetization revealed the non-Kramers Γ(3) doublet ground state with the quadrupolar degrees of freedom. The specific heat exhibits a sharp peak at T(Q)=0.11  K. The increment of T(Q) in magnetic fields and the anisotropic B-T phase diagram are consistent with the antiferroquadrupolar ordered state below T(Q). The entropy release at T(Q) is only 20% of Rln2, suggesting that the quadrupolar fluctuations play a role in the formation of the superconducting pairs below T(c)=0.05  K.

Longitudinal field μSR measurements in applied fields parallel and perpendicular to the c-axis of the hexagonal heavy-fermion antiferromagnet Ce(7)Ni(3) served to monitor the 4f-spin dynamics across the magnetic phase diagram in the B-T plane, which consists of an incommensurate/commensurate antiferromagnetic (AF) section below 1.9 K/0.7 K and below an applied field B of 0.25 T, and for B along the c-axis, of a field-induced magnetic (FIM) section for B≥0.6 T and below 0.5 K. The observed μ(+) spin-lattice relaxation rates reveal persisting spin dynamics across the whole phase diagram, reflect the various phase boundaries and are interpreted to arise in the AF and FIM phases from the Ce3 sublattice (the Ce ions are located on three different sublattices) and in the intermediate phase, viewed as a short range ordered (SRO) state, also from the Ce1 and Ce2 sublattices with slower fluctuation rates. In the paramagnetic regime the Ce1 sublattice displays the slowest spin dynamics. In the FIM phase the fraction of relaxing μ(+) appears to shrink with rising B, evidencing a possible phase separation.