The Single Crystal Growth And Physical Properties Of Heavy Fermion Compound CeCo₂Ga₈ And Related Materials

The heavy fermion physics is an important branch in the field of strong correlation system.The energy scales of heavy fermion materials are various and complex,such as Kondo effect,RKKY interaction,crystal field effect,Coulomb interaction and so on.But the energy scales in different materials tend to be different,so the subtle competition and balance between the interactions creates a lot of nontrivial physical behaviors,such as Kondo effect,heavy fermion superconductivity,quantum critical behavior.This subtle competition and balance can be easily adjust by external parameters,like magnetic field,pressure,chemical doping.The complex nature of heavy fermion physics can be simplified by enhancing one effect.Therefore,the preparation and synthesis of effectively doped heavy fermion materials,as well as the growth of high-quality single crystals,are of great importance to the research,especially the discovery of new heavy fermion compounds based on existing heavy fermion materials.At present,the research on heavy fermion tends to be saturated,which is limited not only by the complexity of strong correlation theory,but also by the discovery of new Kondo lattice materials.In this paper,single crystal CeCo₂Ga₈and its related heavy fermion compounds were successfully synthesized by flux method,and their physical properties were systematically characterized by physical property measurement system.The main contents are as follows:Firstly,we successfully synthesized CeCo₂Ga₈ single crystal by using flux method.Through powder XRD and single crystal characterization,the structure is proved to be consistent with that of polycrystalline reported long ago,which belongs to the orthomorphic system.According to the crystallographic parameters,the material has a quasi-one-dimensional structure,which formed by the Ce-atom chain enclosed by CoGa₉ cages.The resistivity and specific heat data show the quantum critical behavior??^T,C_p/T^-lnT?in heavy fermion physics at low temperatures,and the magnetic susceptibility also shows strong anisotropy.The magnetic susceptibility along the direction of the Ce-atom chain can be well fitted by the one-dimensional spin chain formula.In addition,the band structure calculated by DFT and the resistivity data under pressure further illustrate that CeCo₂Ga₈ should be a quasi-one-dimensional heavy fermion material near the quantum critical point.Secondly,using In-Ga alloy as flux,we have successfully grown CeCoInGa₃single crystal,whose parent compound is CeCoGa₄,belonging to the orthogonal crystal system.Single crystal characterization shows that In-atom completely occupies a crystal position of Ga-atom.This substitution makes the parent compound CeCoGa₄ into a typical heavy fermion Kondo lattice material,with a significant Kondo effect in electrical resistivity and an enhanced electronic specific heat coefficient of 172 mJ/mol K² in specific heat.According to the fitting results,three important energy scales are given:the coherence temperature T^*?50 K,the spin fluctuation temperature T_SF?9 K,and the Fermi liquid temperature T_FL?6 K.The magnetic susceptibility shows an obvious hybridization effect with a broad peak at low temperatures.The anisotropy of this hybridization effect has a close relation with the crystal structure,which was consistent with the relevant theoretical calculation of DFT+DMFT.Therefore,the study on CeCoInGa₃ has reference significance for the chemical doping and anisotropic hybridization.Finally,based on the study of CeCo₂Ga₈ single crystals and the latest developments in the field of heavy fermions,we have successfully synthesized CePd₂Al₈ single crystals by flux method.Both polycrystalline XRD and single crystal characterization confirmed that CePd₂Al₈ is a new Ce-128 structure belonging to the monoclinic system,which is different from the orthogonal structure of CeCo₂Ga₈.Unlike the report on the polycrystalline sample,we observed two successive magnetic phase transitions on the single crystals?antiferromagnetic phase T_N?9.8 K and ferromagnetic phase T_C?8.7 K?and a large magnetic anisotropy.Through the measurement of resistivity,specific heat and magnetic susceptibility with field,we confirmed the existence of antiferromagnetic and obtained a rough T-H phase diagram.In addition,the resistivity under pressure shows that both phases are enhanced at first but then suppressed and merged into a single phase of most probably FM nature at about 12.5 GPa,pointing to potential suppression of FM and related physics at higher pressures in this new class of Kondo lattice compounds.