We report 73Ge-nuclear-quadrupole resonance (NQR) study of heavy-fermion compound CeNi2Ge2. The temperature dependence of the 73Ge nuclear-spin-lattice-relaxation rate 1/T1 indicates the development of magnetic correlations and the formation of a Fermi-liquid state at temperatures lower than TFL=0.4K, where 1/T1T is constant. The 1/T1T decrease below TcNQR=0.1K, whereas resistance decreases below Tconset=0.2K and does not become zero. These results indicate CeNi2Ge2 closely locates to a superconducting quantum critical point.

The field dependence of the Hall resistivity for CeCu6−xAux (x=0.0, 0.10, 0.25 and 0.50) was measured at 0.5K. In this temperature region, the ordinary Hall effect is dominant for CeCu6. Alternatively, the extraordinary contribution due to the skew scattering appears for the Au-substituted compounds, suggesting the localized nature of a 4f-electron.

We present evidence for unconventional superconducting fluctuations in a heavy-fermion compound CeNi2Ge2. The temperature dependence of the Ge-73 nuclear-spin-lattice-relaxation rate 1/T-1 indicates the development of magnetic correlations and the formation of a Fermi-liquid state at temperatures lower than T-FL = 0.4 K, where 1/T1T is constant. The resistance and 1/T1T measured on an as-grown sample decrease below 7(c)(onset) = 0.2 K and T-c(NQR) = 0.1 K, respectively: these are indicative of the onset of superconductivity. However, after annealing the sample to improve its quality. these superconducting signatures disappear. These results are consistent with the emergence of unconventional superconducting fluctuations in close proximity to a quantum critical point from the superconducting to the normal phase in CeNi2Ge2.

We report measurements of resistivity rho in UGe2 at temperatures T down to 0.3 K, pressures P up to 19.8 kbar, and magnetic fields B-appl up to 17.5 T applied along the magnetic easy a axis. The coefficient A of the T-2 term of rho(T) is determined as a function of B-appl and P. In the large-moment ferromagnetic phase (the low-P/high-B-appl phase), A is found to be a function of the single parameter (B-appl-B-x) and approximately obeys a power law A proportional to(B-appl-B-x)(-1/2), where B-x is the transition field from the small- to the large-moment ferromagnetic phase. The T dependence of rho at fields just above B-x suggests a contribution to rho from excitations with a gapped spectrum.

A GdNi single crystal has been prepared by the Czochralski method and studied by measuring the magnetization, electrical resistivity and thermal expansion. The ferromagnetic ordering below TC=69K has been confirmed. The saturated magnetization at 2K was found to be identical (7.2μB/f.u.) along all the three principal crystallographic directions. This result is in agreement with theoretical calculations, which yield magnetic moment of 7.0μB/f.u. for Gd3+ ion and 0.18μB/f.u. for conduction electrons with magnetic moment of the same direction as the Gd moment. An anomalous spontaneous magnetostriction is dominating the thermal expansion behavior below TC. In particular, we have observed a large contraction in the c-direction and a smaller expansion in the a and b directions (nearly identical). The unit cell volume expands below TC (ΔV/V=8×10−4). The observed anisotropy of the magnetostriction in GdNi is attributed to anisotropic magnetoelastic coupling.

The electrical resistivity and magnetoresistance (MR) of single crystalline alpha-Ce have been measured under high pressure and low temperature. It is found that the temperature dependence of resistivity rho(T) at low temperature is described as rho(T) = rho(0) + AT(2) below 10 K, where rho(0) is the residual resistivity and A is the constant. A decreases significantly as pressure increases, which corresponds to the increase of Kondo temperature T-K at high pressure. A seems to be divergent from higher pressures toward 0.3 GPa, which suggests the existence of magnetic phase boundary. MR ratio of alpha-Ce is positive and enhanced by applying pressure. These results are discussed on the basis of theoretical model presented by Kawakami-Okiji. (c) 2005 Elsevier B.V All rights reserved.

The a-axis resistivity in UGe2 is measured in the temperature range between 0.3 and 4.5 K and in magnetic fields up to 17.5 T applied parallel to the a axis, which is the easy axis of magnetization. The T2 coefficient A of the resistivity is 0.008 μ Ω cm/K2 at zero field and is reduced by ∼50% with increasing field to 17.5 T.

Neutron scattering shows that non-Fermi-liquid behavior of the heavy-fermion compound CeNi2Ge2 is brought about by the development of low-energy spin fluctuations with an energy scale of 0.6 meV. They appear around the antiferromagnetic wave vectors (1/21/20) and (003/4) at low temperatures, and coexist with high-energy spin fluctuations with an energy scale of 4 meV and a modulation vector (0.23,0.23,1/2). This unusual energy dependent structure of Imchi(Q,E) in Q space suggests that quasiparticle bands are important.

Neutron scattering shows that non-Fermi-liquid behavior of the heavy-Fermion compound CeNi2Ge2 is brought about by development of low-energy spin fluctuations with an energy scale of 0.6 meV. They appear around antiferromagnetic wave vectors ((1)/(2) (1)/(2) 0) and (00(3)/(4)) at low temperatures, and coexist with high-energy spin fluctuations with an energy scale of 4 meV and a modulation vector (0.23, 0.23, (1)/(2)). The energy dependence of the spin fluctuations is a peculiar character of CeNi2Ge2 which differs from typical heavy-Fermion compounds, and suggests importance of low-energy structures of quasiparticle bands.

We report de Haas-van Alphen effect measurements on UGe2 at pressures P up to similar to18 kbar, which exceeds the critical pressure P-c similar to16 Bar for the suppression of ferromagnetism. Particular attention is given to the complicated pressure dependence of the Fermi surface and effective mass in an intermediate pressure region from similar to11 kbax to P-c.

The ac susceptibility and de Haas-van Alphen (dHvA) effect in UGe2 are measured at pressures P up to 17.7 kbar for the magnetic field B parallel to the a axis, which is the easy axis of magnetization. Two anomalies are observed at B-x(P) and B-m(P)(B-x>B-m at any P), and the P-B phase diagram is presented. The Fermi surface and quasiparticle mass are found to vary smoothly with pressure up to 17.7 kbar unless the phase boundary B-x(P) is crossed. The observed dHvA frequencies may be grouped into three according to their pressure dependences, which are largely positive, nearly constant, or negative. It is suggested that the quasiparticle mass moderately increases as the boundary B-x(P) is approached. DHvA effect measurements are also performed across the boundary at 16.8 kbar.

The magnetic structure of heavy-fermion antiferromagnets Ce(Ni 1- x Pd x ) 2 Ge 2 proximate to the magnetic instability has been studied by elastic neutron scattering using single crystals. For Ce(Ni 0.65 Pd 0.35 ) 2 Ge 2 , antiferromagnetic ordering with an incommensurate propagation vector q =(1/2,1/2,δ); δ∼0.16 is observed below T N =3.4 K. The integrated intensities of magnetic Bragg peaks at 1.8 K are well fitted by assuming a sine-wave-modulated structure with the amplitude 0.55±0.04 µ B and magnetic moments along [110]. For the compound very near the magnetic instability, Ce(Ni 0.90 Pd 0.10 ) 2 Ge 2 , the ordered moment is expected to be reduced to below 0.1 µ B .

We have succeeded in growing a high-quality single crystal of PrNi2Al5, and have measured the electrical resistivity, magnetic susceptibility, magnetization and specific heat. Any magnetic phase transition has not been observed. The crystalline-electric-field (CEF) scheme has been estimated by using the reciprocal susceptibility and a magnetic part of the specific heat. The magnetic anisotropy has been well explained by the CEF effect. The analytical result of the CEF effect shows that this compound has a singlet ground state and that the CEF energy in 4f electrons from the ground state to the first excited state is 43 K. The Fermi surfaces and the cyclotron effective masses have been investigated by means of de Haas-van Alphen effect. It is found that the Fermi surfaces of PrNi2Al5 are almost the same as those of LaNi2Al5.

A complete set of the 195Pt Knight-shift (KS) data on the superconducting (SC) state in UPt3 identified the spin structure of the Cooper pair corresponding to the multiple SC phases. UPt3 was acclaimed as the first odd-parity superconductor including a non-unitary pairing state characterized by the two-component d vector like db+idc at low T and low H [H. Tou et al., Phys. Rev. Lett. 77 (1996) 1374; 80 (1998) 3129]. We have shed further light on these novel results through a comparison with the singlet even-parity anisotropic superconductors CeCu2Si2 and UPd2Al3. In the singlet pairing state, the fractional decrease in KS below Tc,δKobs is independent of the crystal direction. We have found that δχobs=(NAμB/Ahf)δKobs where Ahf is the hyperfine coupling constant, is in good agreement with spin susceptibilities χγel calculated from an enhanced electronic specific heat γel and χnmr from the quasiparticle Korringa relation T1TKs2=const. This gives direct evidence that the χs of heavy quasiparticles in CeCu2Si2 and UPd2Al3 is rather isotropic and decreases to zero as T→0 due to the Cooper-pair formation. On the other hand in UPt3, the δχobsb,cs along the b- and c-axis in the non-unitary-pairing state (B phase) are two orders of magnitude smaller than χγel and χnmr. These anomalously small values for δχobsb,cs may suggest either that the spin degree of freedom in the B phase is not perfectly locked to the a-axis or that χs is not enhanced although γel is. The latter is theoretically pointed out by Ikeda and Miyake [J. Phys. Soc. Japan 66 (1997) 3714] to be possible if 5f electrons in the non-Kramerse singlet ground state for 5f2 are hybridized with conduction electrons. We need further effort towards coherent understanding of a microscopic mechanism leading to the occurrence of the odd-parity superconductivity in UPt3.

We have performed transport and susceptibility measurements on single-crystal CeNi2 Ge2 under high pressure and magnetic field. Under pressure a 30% decrease of the resistivity is found below 300 mK which could be due to the onset of superconductivity. Assuming this we have established the phase diagram of the superconducting phase under pressure and magnetic field. The analysis of H c 2 and the slope at Tc in comparison to a previously published report of superconductivity at ambient pressure might indicate a change in the order parameter with pressure. The normal state resistivity at ambient pressure does not show a quadratic temperature dependence. Under pressure a quadratic dependence is found and we show that the parameters of the resistivity and the susceptibility obey a simple scaling law. This scaling breaks down however when approaching the magnetic instability.

We report 101Ru NQR studies in substituted systems of a non-magnetic heavy fermion compound CeRu2Si2, Ce1−xLaxRu2Si2 (x=0.05, 0.08) and CeRu2(Si1−zGez)2 (z=0.05, 0.078). The Kondo temperature TK and the characteristic temperature of the Fermi liquid TFL, estimated from the 101Ru nuclear spin–lattice relaxation rate 1/T1, decrease with increasing x or z. A magnetic ordering is observed for z=0.078. The SCR theory is applied for an interpretation of the T-dependence in 1/T1, and it is suggested that the magnetic to non-magnetic transition against x or z may occur as a first-order type in these systems without passing through the quantum critical point (TN→0).

We have measured specific heat and electrical resistivity of Ce(Ni1−xPdx)2Ge2 (x=0.09 and 0.12) single crystals with antiferromagnetic ground state. For x∼0.12 crystal, there is no obvious rise in the electrical resistivity around the Néel temperature TN. This antiferromagnetic ordering might be understood as the itinerant antiferromagnetism of heavy-quasiparticles without the gapping behavior.

Neutron scattering experiments have been performed in order to study the antiferromagnetic correlation in UPt3 at ultralow temperatures. The (0.501) antiferromagnetic peak was observed down to 20mK. The linewidth exhibits a remarkable narrowing with decreasing temperature, and a resolution-limited peak is observed below 20mK. This is direct evidence for the long-range antiferromagnetic correlation in UPt3.

Magnetoresistance and de Haas-van Alphen measurements have been performed to investigate the Fermi-surface property of LaNi 2 Al 5 , which is a reference material of the magnetic dense-Kondo compound CeNi 2 Al 5 . Thirteen branches with the frequencies from 1.25 ×10 6 to 101 × 10 6 Oe have been observed in the angular-resolved dHvA measurements, and the magnetoresistance shows the existence of open orbits. The results are well explained by the Fermi surfaces obtained from an FLAPW band-structure calculation.