Synthesis, crystal structure, and magnetic properties of novel 2D kagome materials RE₃Sb₃Mg₂O₁₄ (RE = La, Pr, Sm, Eu, Tb, Ho): Comparison to RE₃Sb₃Zn₂O₁₄ family

The crystal structures and magnetic properties of RE₃Sb₃Mg₂O₁₄ (RE = La, Pr, Sm, Eu, Tb, Ho) with a perfect kagome lattice are presented and compared to RE₃Sb₃Zn₂O₁₄. Rietveld structure refinements were performed using X-ray diffraction data, indicating that the layered compounds are fully structurally ordered. The compounds crystallize in a rhombohedral supercell of the cubic pyrochlore structure, in the space group R-3m. Magnetic susceptibility measurements show no signs of magnetic ordering above 2 K. The RE₃Sb₃Mg₂O₁₄ family is similar to that of RE₃Sb₃Zn₂O₁₄; however, the series reported here features a fully ordered distribution of cations in both the nonmagnetic antimony and magnetic rare earth kagome lattices. Unlike the offsite disorder that Zn²⁺ experiences in RE₃Sb₃Zn₂O₁₄, the magnesium sites in RE₃Sb₃Mg₂O₁₄ are completely ordered. Here we compare the magnetic properties in both series of kagome compounds to determine how significant Zn²⁺'s positional ordering is within this structure type. The compounds reported here appear to be relatively defect-free and are therefore model systems for investigating magnetic frustration on an ideal 2D rare earth kagome lattice.