Abstract

We have performed powder neutron diffraction measurements for Sr₂TbRuO₆ at 10 K and room temperature. It has been found that the crystal structure of this compound is a distorted perovskite (a = 5.7932(2) Å, b = 5.8107(1) Å, c = 8.2011(3) Å and β = 90.249(2)°) with the space group P2₁/n (No.14) and a 1 ∶ 1 ordered arrangement of Ru⁵⁺ and Tb³⁺ over the 6-coordinate B sites. Data collected at 10 K show that Sr₂TbRuO₆ has long range antiferromagnetic ordering involving both Ru⁵⁺ and Tb³⁺. Each of these ions orders in a type I arrangement. The direction of the magnetic moments is canted by ca. 20° from the c axis. The magnetic susceptibility and specific heat measurements show the existence of magnetic transitions at 32 K and 41 K.

The magnetic properties of Sr₂TbRu_{1 − x}Ir_xO₆ (0 < x < 1) are also reported in this paper. The structural data and the value of the effective magnetic moment indicate that these compounds adopt the valence configuration of Sr₂Tb³⁺(Ru_{1 − x}Ir_x)⁵⁺O₆ (x = 0.0–0.7) or Sr₂Tb⁴⁺(Ru_{1 − x}Ir_x)⁴⁺O₆ (x = 0.85–1.0). Evidence for the presence of a mixed valence state was not found. The magnetic transition temperature for Sr₂Tb³⁺(Ru_{1 − x}Ir_x)⁵⁺O₆ decreases with increasing x. On the other hand, that for Sr₂Tb⁴⁺(Ru_{1 − x}Ir_x)⁴⁺O₆ increases with x.