Studies on magnetic susceptibility and specific heat for 6H-perovskite-type oxides Ba3LnIr2O9 (Ln=La, Nd, Sm-Yb)

Magnetic properties of the 6H-perovskite-type oxides Ba₃LnIr₂O₉ (Ln=La and Nd: monoclinic; Ln=Sm-Yb: hexagonal symmetry) were investigated. For all the title compounds, a specific heat anomaly was found at 5.3-17.4 K. At the corresponding temperatures, the magnetic susceptibilities show a slight variation in its gradient. These magnetic anomalies suggest the magnetic ordering of the magnetic moments (S=1/2) remaining in the Ir^4.5+₂O₉ face-shared bioctahedra. In addition, the Ln³⁺ ions show the onset of the antiferromagnetic ordering around these temperatures. The Ba₃NdIr₂O₉ only shows a ferromagnetic behavior below 17.4 K with a remnant magnetization of 1.25 μ_B. This behavior may be due to the ferromagnetic ordering of the Nd³⁺ moments.