Magnetic properties and neutron diffraction study of double perovskites Ca₂LnRuO₆ (Ln = Y, La-Lu)

Magnetic properties of double perovskites Ca₂LnRuO₆ (Ln ≤ Y, La-Lu) were investigated. From the magnetic susceptibility and specific heat measurements, it is found that all the title compounds show an antiferromagnetic transition (T_N ≤ 10-34 K), and that the antiferromagnetic ordering of Ru⁵⁺ ions with a doublet ground state occurs below these temperatures. In these compounds, the larger Ln ions tend to occupy the A site of the perovskite ABO₃, while the smaller Ln ions tend to occupy the B site. The Nd ions in Ca₂NdRuO₆ are situated at the A site and show an antiferromagnetic transition at 1.6 K, which is much lower than T_N ≤ 11.5 K. On the other hand, the Yb ions in Ca₂YbRuO₆ are situated at the B site, and a long-range antiferromagnetic ordering due to both Yb³⁺ and Ru⁵⁺ ions occurs at 34 K. The magnetic structure of Ca₂YbRuO₆ was determined by powder neutron diffraction measurements; it shows a non-collinear arrangement between Yb³⁺ (∼1.3 ν_B) and Ru ⁵⁺ (∼1.7 ν_B) moments.