Structural, electronic and magnetic properties of layered REB _2C compounds (RE=Dy, Tm, Lu)

摘要

The crystal structure of LuB _2C has been determined from single crystal and powder X-ray diffraction data. It crystallizes in the orthorhombic space group Pbam (a=6.7429(1) ?, b=6.7341(1) ?, c=3.5890(1) ?, Z=4, R1=0.024 (wR2=0.059) for 436 reflections with I _o>2σ (I _o)). The compounds REB _2C (RE=Y, Tb-Lu) are isotypic. The boron and carbon atoms form infinite, planar two-dimensional nets which alternate with sheets of rare-earth metal atoms. Inside the nonmetal atom nets, a coloring with fused B _2C _2 rhombuses and B _5C _2 heptagons is proposed, supported by NMR experiments and density functional theory calculations. The calculated density of states of LuB _2C indicates this compound to be metallic. The magnetic properties of the isotypic compound TmB _2C, has been measured in the temperature range 2 K3 T a metamagnetic transition is encountered. The temperature dependence of the electrical resistivity proves the metallic character of the TmB _2C compound as well as the AFM ordering.