The Structure And Magnetic Properties Of Rare Earth Metals And White Compounds

Among the large body of rare-earth intermetallics, the group of Ce and Yb based compounds have received particular attention in both experimental and theoretical respects due to their rich variety of unuaual physical properties such as intermediate valence, dense Kondo effect, heavy fermion and superconductivity etc. The extraordinary behavior found for most of these compounds is mainly associated with the 4f electronic configuration which is usually 4f1 for Ce and 4f13 for Yb. Owing to the proximity of the respective 4f1 and 4f13 configuration to an empty 4f0 or a filled 4f14 shell, the electronic configuration may become unstable, which cause a variety of observable physical phenomena dua to charge or spin fluctuation. Associated with such fluctuation there occurs a considerable hybridization between the localized 4f electrons and the delocalized conduction electrons.Because the spatial extension of the 4f wave function is rather small (less than~0.5 ?), the concentration of magnetic 4f impurities in a non-magnetic host can be surprisingly high without violating the conditions necessary for the Kondo effect to occur. This leads to a group of alloys termed dense Kondo system. When the magnetic ions build up a regular sublattice, so-called Kondo lattice is then realized. Kondon lattices frequently shows striking similarities with the dilute Kojdo system at high temperature. Because of the interactions between the magnetic ions of the lattice, the energy gain provided by the singlet formation should be less than that in the single–impurity case. This implies that the singlet formation should not occur when the intersite interaction is sufficiently strong. In that case, compounds order magnetically with reduced magnetic moments.The outstanding properties of rare-earth based intermetallic systems have triggered much theoretical and experimental effort. The first theoretical model explaining the mechanism of the logarithmic resistivity increase in dilute magnetic alloys was put forward in 1964 by Kondo. Later a successful description of dense Kondo system, containing 4f magnetic impurities of a larger orbital degeneracy such as Ce (J=5/2) and Yb (7/2), was given by the Coqblin-Scherieffer model. A unified interpretation to valence fluctuation phenomena observed in rare-earth systems, which is closely related to the Kond problem, however is still lack until today, because it involves a complicated many-body problems such as hybridization, intra-site correlation, electron screening and electron-phonon coupling etc.In later 1980s, a class of Yb based ternary YbCu5-xMx(M=In,Ag,Au,Pd,Alå'ŒGa)compounds were found to exhibit a rich variety of low-temperature ground state properties including mixed valence, Kondo lattice, heavy fermion and antiferromagnetic ordering. The various ground state phenomena originate from the interaction between 4f electrons and conduction electrons as a consequence of mutually competing mechanisms such as on-site Kondo effect , inter-site RKKY interaction and crystal-field splitting effect on ground multiplet. In persuing the universal understanding of strongly correlated electron phenomena, the ternary YbCu5-xMx system, as a promising chemical candidate, is being investigated extensively.We first reviewed the research achievements of rare-earth intermetallics and new progress; then we synthesized C15b-type YbCu5-xInx samples with arc-melting method. Then we chiefly studied their structure and magnetic propertied of the YbCu5-xInx system. Main results of my work are shown as following:Rare-earth intermetallics ternary C15b-type YbCu5-xInx samples were prepared by arc-melting method. Polycrystalline XRD shows that the samples have a cubic C15b-type structure, and we also found that the lattice constant of YbCu5-xInx compounds increases linearly with In-content increasing. The M—T curves, which measured by SQUID technique, reveals that the first-order valence transition in YbCu5-xInx shifts to higher temperature and becomes broadened significantly with decreasing In-content and above 150K the samples display Curie-Weiss paramagnetic behavior, the Yb ion was localized trivalent state(Yb3+, 4f13, J=7/2,μeff=4.54μB).