Preparation And Physical Properties Of The Heavy Fermion Compounds R₂T₁₂As₇（R=Ce,Yb;T=Ni,Pd,Co）

Quantum criticality describes the collective quantum fluctuations of a matter undergoing a second-order phase transition at zero temperature. In many heavy-Fermion systems, the magnetic phase transition temperature can be continuously tuned to zero, attributed to their low energy scale. Anomalous physical properties, e.g. coexistence of superconductivity and magnetism, non-Fermi liquid behavior, are emerging in the quantum critical region. Elucidation of the quantum critical phenomenon using a unified picture remains highly important.The content of the dissertation is divided into five chapters:The Chapter 1 reviews the recent progress on the studying of heavy-Fermion systems.The Chapter 2 presents some theoretical concepts and reviews major theories of quantum phase transitions.In Chapter 3, we study the moderate heavy fermion compound Yb2Ni12P7 synthesized by tin-flux method. We systematically investigated its structure, composition, magnetization, electrical resistivity and specific heat. It is found that this compound shows a paramagnetic ground state, with Fermi liquid behavior at low temperature.In Chapter 4, we synthesized a new heavy-Fermion compound Ce2Co12As7 using self-flux method. Measurements of electrical resistivity and specific heat indicate that this system undergoes a ferromagnetic transition at Tc=18K. The magnetization measured at different field orientation show strong anisotropic effect.In Chapter 5, we study the possible quantum criticality in polycrystalline compounds Ce2Ni12As7-YPY and Ce2Ni12-xPdxAs7, synthesized by a solid state reaction method, and in single crystalline compounds Ce2Ni12As7, Ce2Pd12As7, synthesized by self-flux method. The structure and physical properties are studied with varies measurements. It is found that the unit cell volume increases linealy with reducing the concertration of P in Ce2Ni12As7.YPY and increasing the concertration of Pd in Ce2Ni12-xPdxAs7. Preliminary results indicate that Ce2Ni12As7 is near the ferromagnetic quantum critical point but Ce2Pd12As7 is near the field-induced antiferromagnetic quantum critical point.In summary, these new compounds seems to provide a good promise for studying magnetic quantum criticality and the related physics.