Shinsaku Kambe

Application of the SCR spin fluctuation theory for the magnetic instability in heavy fermion system Ce1-xLaxRu2Si2

We have applied the self-consistent renormalized (SCR) spin fluctuation theory to calculate several physical quantities measured for Ce 1- x La x Ru 2 Si 2 ( x =0, 0.05 and 0.075), namely the specific heat, resistivity, thermal expansion, spin-lattice relaxation and inelastic neutron scattering. A quantitative agreement between experiments and the theory has been obtained in all cases, indicating that the spin fluctuations dominate the thermal and dynamical properties near the magnetic instability in this system. Comparisons are also made with the recent renormalization group approach to the quantum critical point in itinerant systems.

Broadening Mechanism of Resistive Transition under Magnetic Field in Single Crystalline (La1-xSrx)2CuO4

The resistive transitions near the superconducting critical temperature were measured under magnetic field up to 5 T on a FZ-grown high-quality single crystal (La0.93Sr0.07)2CuO4 (Tc=37.5 K) The crystal was sufficiently large along the c-axis that the dc four-probe method could be applied along this axis as well as along the usual a-b plane. It was found that the width of the temperature region over which the resistive transition is broadened depends only on the relative orientation between the magnetic field and the crystalline c-axis, but not on that between the field and the current. It indicates that the mechanisms based on the fluxoid motion, such as the flux creep model, the Kosterlitz-Thouless transition model and the superconducting glassy state model, are unlikely to explain the broadening of the resistive transition under magnetic fields in (La1-xSrx)2CuO4.

Novel Phase Transition in CeRu2Al10 Probed by 27Al-NQR/NMR –No Evidence of Magnetic Ordering–

The 27 Al-NQR/NMR measurements of CeRu 2 Al 10 were carried out to clarify the unusual phase transition at T 0 =27 K. Distinct NQR peaks associated with five nonequivalent Al sites have been observed at T > T 0 , and each peak is successfully assigned to their respective Al sites. Below the transition temperature T < T 0 , each peak simply splits into two peaks except for one site. This indicates that the phase transition is not accompanied by magnetic order, but is presumably associated with the onset of structural transition with lowering symmetry. The nuclear spin–lattice relaxation rate 1/ T 1 suggests a local moment picture above T * ∼60 K, and the development of Kondo coherence toward T 0 . Below T 0 , 1/ T 1 shows a gaplike decrease with a gap magnitude of 106 K, being consistent with the macroscopic measurements. The Korringa term below 10 K after the gaplike decrease suggests a gap opening over a portion of the Fermi surface.

The heavy fermion compound CeRu2Si2: Magnetic instability, lattice quasicollapse and metamagnetism

Abstract The physical properties of the heavy fermion compound CeRu 2 Si 2 are reviewed. Since this compound is close to a magnetic instability, special attention is paid to its magnetization in which a metamagnetic-like transition occurs at a field H M of 7.7 T and to the strong coupling between this effect and the volume, leading to a quasi-collapse of the lattice. It is shown that the value of the differential susceptibility at H M reaches an intrinsic finite limit at very low temperature. Different theoretical models are discussed.

Evidence for Appearance of an Internal Field in the Ordered State of CeRu2Al10 by µ+SR

We report zero-field µ + SR measurements made at J-PARC on CeRu 2 Al 10 . Below the phase transition temperature T 0 ∼27 K, a clear modulation of µ + polarization due to an internal field is observed, indicating that magnetic ordering takes place. Compared with the internal field expected from the effective magnetic moment in the disordered state, the observed internal field at the µ + site is quite small. This indicates that the ordered Ce magnetic moment is small (∼10 -2 µ B ) and/or the nearest pair of Ce magnetic moments are mutually anti-parallel. The T -dependence of the internal field is somewhat peculiar, suggesting that another ordering is taking place as well.

Recent Advances in the 5f-Relevant Electronic States and Unconventional Superconductivity of Actinide Compounds

Recent advances in the understanding of the 5 f -relevant electronic states and unconventional superconducting properties are reviewed in actinide compounds of UPd 2 Al 3 , UPt 3 , URu 2 Si 2 , UGe 2 , and PuRhGa 5 . These are based on the experimental results carried out on high-quality single crystal samples, including transuranium compounds, which were grown by using combined techniques. The paring state and the gap structure of these superconductors are discussed, especially for the corresponding Fermi surfaces which were clarified by the de Haas–van Alphen experiment and the energy band calculations. A detailed systematic study using the NQR/NMR spectroscopy reveals the d -wave superconductivity in PhRhGa 5 and the difference of magnetic excitations due to the difference of ground states in U-, Np-, and Pu-based AnTGa 5 (T: transition metal) compounds.

Field-induced renormalization observed by magnetoresistance in CeRu2Si2

Abstract We have measured the magnetoresistance of two CeRu2Si2 specimens issued from the same single crystal (with j parallel to the a-axis and parallel to the c-axis, respectively) at several fixed temperatures between 0.02 and 1.2 K in magnetic field up to 9 T applied parallel to the c-axis. All ϱ vs. H curves show a maximum at the metamagnetic-like transition field B ∗ = 7.7 T . When measured in constant applied field, the resistivity exhibits a quadratic temperature dependence (ϱ = ϱ0 + AT2) at low temperature ( B ∗ as well as for B > B ∗ . The applied field brings about a larger change of the A term for j // a than for j // c, indicating that the field-induced mass renormalization occurs anisotropically in this compound. The magnitude of the mass enhancement given by the relation A ∝ γ , is consistent with the previous enhancement derived from magnetization measurements via the Maxwell relation.

Characteristic of metamagnetic transition in CeRu2Si2 revealed with hall mobility

Field dependence of the Hall resistivity has been measured below and above a metamagnetic-like transition (MT) at 50 mK-2 K in a high quality single crystal CeRu2Si2. The MT in the Fermi-liquid region is regarded as a continuous modification of resonance quasi-particle band near the Fermi level and no drastic change of carrier density is observed. In contrast, the MT in the incoherent region exhibits no clear change of effective mass or inelastic scattering time. The strong modification of the MT by the coherent effect is discussed.

Magnetic correlations in Ce0.925La0.075Ru2Si2

Inelastic neutron scattering experiments were performed to study the spin dynamics of the heavy fermion compound Ce0,925La0.075Ru2Si2. This composition corresponds to the borderline of the magnetic-non magnetic transition in the family of alloys Ce1−xLaxRu2Si2. Short range magnetic correlations of an inelastic nature characterize this system in addition to a small ordered moment of the order of 0.02μB which appears below 2 K. Comparison with the magnetic excitation spectrum of the Pauli paramagnet CeRu2Si2 is given from the viewpoint of recent work on phase transitions near the magnetic instability point.

Switching of the magnetic interactions from antiferromagnetic to ferromagnetic in the heavy-fermion compound under high magnetic field

Inelastic neutron scattering studies of under high magnetic field are reported. The dynamic short-range antiferromagnetic correlations are progressively replaced by static long-range ferromagnetic order when the field is increased. A simple interpretation using a phenomenological model leads to the conclusion that the exchange interactions are field dependent and that their weight is shifted from the antiferromagnetic point to the ferromagnetic point as the field changes.