Crystal structures and magnetic properties of magnetically frustrated systems BaLn2O4 and Ba3Ln4O9 (Ln = lanthanide)

The crystal structures and magnetic properties of the ternary oxides BaLn(2)O(4) (Ln = Pr, Nd, Sm-Ho) and Ba(3)Ln(4)O(9) (Ln = Dy-Lu) have been investigated. These two series of compounds have the CaFe2O4-type structure with space group Pnma and a perovskite-related structure with space group R3, respectively. In both structures, the Ln ions locally adopt a triangle-based array, which has the possibility of resulting in a geometrically frustrated magnet. From the magnetic susceptibility measurements, it was found that some compounds show a magnetic anomaly at 2.2-4.0 K and the others are paramagnetic down to 1.8 K. The results of the specific heat measurements show that these compounds show a long-range antiferromagnetic ordering of Ln ions at 1.7 K (for BaNd2O4), 2.6 K (BaGd2O4), 0.8 K (BaHo2O4), and 4.0 K (Ba3Er4O9).