P. Haen

Metamagnetic-Like Transition in CeRu2Si2?

Extensive magnetization and magnetoresistivity experiments on CeRu2Si2 are described, with special emphasis on the metamagnetic-like transition that occurs atH*=80 kOe. By contrast to the low-field susceptibility, the differential susceptibility atH* almost diverges atT→0. It is suggested that high magnetic fields (H>H*) restore a situation where the interactions between particles have collapsed. Comparison is made with other well-known examples: TiBe2, UPt3, TmSe, and3He.

Metamagnetic CeRu2Si2: New perspectives for heavy-fermion studies in high fields

Abstract Interesting magnetic effects have recently been reported to occur in the normal phase of heavy-fermion systems. Among them are the metamagnetic properties of UPt 3 and CeRu 2 Si 2 ( H M = 20 and 8 T). High-pressure magnetization and magnetoresistance, as well as magnetostriction measurements have been performed on CeRu 2 Si 2 . The magnetostriction data imply a remarkable scaling behavior for the magnetization as a function of P and thus a relation between H M and the characteristic Fermi-liquid energy k B T ∗ . The magnetoresistance suggests that the field enhancement of the effective mass derived from the specific-heat γ( H ) leads to the observed transition at H M for a critical value of m ∗ which is pressure independent.

The magnetic instability in the heavy fermion compounds Ce1?x La x Ru2Si2

The magnetization and the specific heat of Ce1−xLaxRu2Si2 with x≤0.13 are reported with special attention to the effect of magnetic field and the role of lanthanum doping. Evidence is given of differences between the undoped (x=0) and the solid solution (x≠0) cases. A common feature is the occurrence of well-defined anomalies in the magnetization at the “metamagnetic” fieldHM independently of whether the ground state is one of long-range order or Pauli paramagnetism. Forx=0, the ground state appears to be a Pauli paramagnet for any strength of the magnetic field; quantum fluctuations or deviations from an ideal lattice may prevent the occurrence of a true static magnetic transition.

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.

Itinerant metamagnetism of CeRu2Si2: bringing out the dead. Comparison with the new Sr3Ru2O7 case

Focus is given on the macroscopic and microscopic experimental works realized during a decade on the clear case of itinerant metamagnetism in the heavy fermion paramagnetic compound CeRu2Si2. Emphasis is made on the feedback between the band structure, the exchange coupling and the lattice instability. Sweeps in magnetic field, pressure and temperature feel the pseudogap of this strongly correlated electronic system as well as its equivalent CeRu2Ge2 at a fictitious negative pressure. Some mysteries persist as the complete observation of the Fermi surface above the metamagnetic field HM and the detection of the dynamical ferromagnetic fluctuation near HM. The novelty of the bilayer ruthenate Sr3Ru2O7 is discussed by comparison. Despite differences in spin and electronic dimensionality many common trends emerge.

High-field magnetostriction in the pseudo-metamagnetic heavy-fermion system CeRu2Si2

Low-temperature magnetostriction experiments have been performed on CeRu2Si2 single crystals in magnetic fields up to 15T. WhenH is applied parallel to the tetragonalc-axis, a very large expansion is observed in all lattice directions. A pronounced anomaly occurs at a field close to the “metamagnetic” threshold. The results are discussed with use of thermodynamic relations and support a very simple scaling behavior for the pressure dependence of the magnetization.

Fermi liquid aspects in valence fluctuating systems

Abstract Low temperature properties of quasi-trivalent non-cubic compounds of cerium (CeAl 3 , CeCu 6 and CeRu 2 Si 2 ) are discussed with special emphasis on the role of the degeneracy of the ground state and of the symmetry of the lattice in the interactions between f electrons. In CeRu 2 Si 2 , an interesting new phenomenon, the occurrence of a polarized phase in a high magnetic field, is reported. The entrance in the intermediate valence regime and the possibility of couplings characteristic of a lattice are discussed.

Transport properties under magnetic fields of the heavy fermion system CeRu2Si2 and related compounds (Ce, La)Ru2Si2

Measurements of thermoelectric power (TEP) and thermal conductivity of single crystals CeRu2Si2 and Ce1−xLaxRu2Si2 are reported with special emphasis on the effect of the magnetic field. The roles of the crystal electric field splitting and the Kondo effect on TEP curves are debated. The TEP results at low temperature are analyzed with a two-band model, and the parameters are compared with those extracted from the thermodynamic measurements. In CeRu2Si2 the occurrence of a coherent regime at very low temperature discussed. The influence of the magnetic field on the TEP and the thermal conductivity is investigated and related with the occurrence of the metamagnetic-like transition already reported in magnetization measurements.

Kondo behavior of YbAgCu4

Abstract Calorimetric and magnetic measurements characterize YbAgCu4 as a Kondo lattice system. The specific heat, the magnetization and the susceptibility can be accounted for using the results for the J = 7 2 Coqblin-Schrieffer model with T0 ≅ 150 K.

Grüneisen parameters of heavy fermion systems

Abstract We discuss recent thermal expansion measurements on single crystalline samples of the heavy fermion compounds CeCu6, CeRu2Si2, URu2Si2, UBe13 and UPt3, and compare the results with existing specific heat data. The resulting Gruneisen parameters ( Г = α v V m / KC ) are anomalously large at low temperatures and vary rapidly with temperature. This implies that a single energy parameter can describe the electron-electron interaction only at very low temperatures.