Synthesis, Crystal Structure, Local Structure, and Magnetic Properties of Polycrystalline and Single-Crystalline Ce₂Pt₆Al₁₅

Asymmetry, such as non-centrosymmetry in the crystal or chiral structure and local symmetry breaking, plays an important role in the discovery of new phenomena. The honeycomb structure is an example of an asymmetric structure. Ce (Formula presented.) Pt (Formula presented.) Al (Formula presented.) is a candidate for a frustrated system with honeycomb Ce-layers, which have been reported to show near the quantum critical point. However, the ground state of Ce (Formula presented.) Pt (Formula presented.) Al (Formula presented.) depends on the sample, and analysis of the crystal structure is difficult due to the presence of stacking disorder. We synthesized polycrystalline Ce (Formula presented.) Pt (Formula presented.) Al (Formula presented.) using arc melting method (AM-Ce (Formula presented.) Pt (Formula presented.) Al (Formula presented.)) and single-crystalline Ce (Formula presented.) Pt (Formula presented.) Al (Formula presented.) using flux method (F-Ce (Formula presented.) Pt (Formula presented.) Al (Formula presented.)). The prepared samples were characterized by electron probe micro-analysis (EPMA), single and powder X-ray diffraction methods, measured magnetic properties and X-ray absorption spectroscopy (XAS). The composition ratio of AM-Ce (Formula presented.) Pt (Formula presented.) Al (Formula presented.) was stoichiometric, although it contained a small amount (i.e., a few percent) of the impurity Ce (Formula presented.) Pt (Formula presented.) Al (Formula presented.). Meanwhile, the composition ratio of F-Ce (Formula presented.) Pt (Formula presented.) Al (Formula presented.) deviated from stoichiometry. The X-ray absorption fine structure (XAFS) spectrum of AM-Ce (Formula presented.) Pt (Formula presented.) Al (Formula presented.) at the Ce L (Formula presented.) -edge was similar to that of CeF (Formula presented.), which possesses the Ce (Formula presented.) configuration, indicating that the valence of Ce in Ce (Formula presented.) Pt (Formula presented.) Al (Formula presented.) is trivalent; this result is consistent with that for the magnetic susceptibility. To determine the precise structure, we analyzed the extended X-ray absorption fine structure (EXAFS) spectra of Ce L (Formula presented.) - and Pt L (Formula presented.) -edges for Ce (Formula presented.) Pt (Formula presented.) Al (Formula presented.), and found that the EXAFS spectra of Ce (Formula presented.) Pt (Formula presented.) Al (Formula presented.) can be explained not as a hexagonal Sc (Formula presented.) Fe (Formula presented.) Si (Formula presented.) -type structure but, instead, as an orthorhombic structure with honeycomb structure.