RESEARCH ON SPIN QUANTUM FLUCTUATION AND ORDERING PROCESS OF ITINERANT HEAVY FERMION

In Ce(Ru-D21-x-D2Rh-D2x-D2)-D22-D2Si-D22-D2compound，x-dependence of the material is investigated in detail.In Ru rich side，the ground state is Fermi liquid for x&lt；0.03and an anisotropic spin density wave(SDW)appears in0.03&lt；x&lt；0.4 with maximum T ei D2N锡D2=5.5K at x=0.15。The nature of the anisotropic SDW is characterized by the anisotropic anomaly in the resistivity below T I D 2.The anisotropy of the SDW is discussed from the view point of nesting of the Fermi surfaces of itinerant heavy fermion quasi-particle bands.Another interesting nature is non-Fermi liquid behavior observed for x=0.4 and 0.5。Appearance of quantum Griffiths‘s like phase is indicated for x=0.5 form the measurements ofµSR，ac susceptibility and nonlinear susceptibility。The temperature dependence of the susceptibility and the magnetoresistance with 0.1T dc field are well explained in terms of the mean field theory based on spin fluctuations.The phase transition of URu I D22个D2 at 17.5K(=T个D20个D2)is considered to be due to quadrupolar ordering from the behaviors of sharp anomaly in nonlinear susceptibility at T个D20个D2 and very large consumption of entropy below T i D20个D2 compared to small staggered ordered moment，0.02µm(B)。We recently found that the phase transition is not due to magnetic origin by the neutron scattering experiment under pressure.The susceptibility and magnetization in dilute alloys of U I D2X II D2 LA I D 21-X D 2 Ru I D 22 ii D 2 Si I D 22 D 2 are well explained by assuming non-Kramers doublet ground state of the J=4 crystalline field level.From these experiments，the phase transition of URu I D22 I D 2 Si I D 22 D 2 at T I D 20 I D 2 is understood by the model of quadrupolar ordering of non-Kramers doublet which coexists with antiferromagntic short range order.

In Ce(RuィイD21-xィエD2RhィイD2xィエD2)ィイD22ィエD2SiィイD22ィエD2 compound, x-dependence of the material is investigated in detail. In Ru rich side, the ground state is Fermi liquid for x < 0.03 and an anisotropic spin density wave (SDW) appears in 0.03 < x < 0.4 with maximum TィイD2NィエD2 = 5.5 K at x = 0.15. The nature of the anisotropic SDW is characterized by the anisotropic anomaly in the resistivity below TィイD2NィエD2. The anisotropy of the SDW is discussed from the view point of nesting of the Fermi surfaces of itinerant heavy fermion quasi-particle bands. Another interesting nature is non-Fermi liquid behavior observed for x = 0.4 and 0.5. Appearance of quantum Griffiths's like phase is indicated for x = 0.5 form the measurements of μ SR, ac susceptibility and nonlinear susceptibility. The temperature dependence of the susceptibility and the magnetoresistance with 0.1 T dc field are well explained in terms of the mean field theory based on spin fluctuations. The phase transition of URuィイD22ィエD2 at 17.5K(=TィイD20ィエD2) is considered to be due to quadrupolar ordering from the behaviors of sharp anomaly in nonlinear susceptibility at TィイD20ィエD2 and very large consumption of entropy below TィイD20ィエD2 compared to small staggered ordered moment ,0.02μ(B). We recently found that the phase transition is not due to magnetic origin by the neutron scattering experiment under pressure. The susceptibility and magnetization in dilute alloys of UィイD2XィエD2LAィイD21-XィエD2RuィイD22ィエD2SiィイD22ィエD2 are well explained by assuming non-Kramers doublet ground state of the J = 4 crystalline field level. From these experiments, the phase transition of URuィイD22ィエD2SiィイD22ィエD2 at TィイD20ィエD2 is understood by the model of quadrupolar ordering of non-Kramers doublet which coexists with antiferromagntic short range order.