Structural, electronic and magnetic properties of layered REB2C compounds (RE=Dy, Tm, Lu)

Abstract

The crystal structure of LuB2C has been determined from single crystal and powder X-ray diffraction data. It crystallizes in the orthorhombic space group Pbam (a=6.7429(1)Å, b=6.7341(1)Å, c=3.5890(1)Å, Z=4, R1=0.024 (wR2=0.059) for 436 reflections with Io>2σ(Io)). The compounds REB2C (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 B2C2 rhombuses and B5C2 heptagons is proposed, supported by NMR experiments and density functional theory calculations. The calculated density of states of LuB2C indicates this compound to be metallic. The magnetic properties of the isotypic compound TmB2C, has been measured in the temperature range 2K<T<300K and in various external fields up to B=7T. The sample undergoes an antiferromagnetic (AFM) transition at TN=12K, and at fields B>3T a metamagnetic transition is encountered. The temperature dependence of the electrical resistivity proves the metallic character of the TmB2C compound as well as the AFM ordering.