Magnetic properties and crystal structures of ordered perovskites Sr2TbRu1-xIrxO6

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) Angstrom, b = 5.8107(1) Angstrom, c = 8.2011(3) Angstrom and beta = 90.249(2)degrees) with the space group P2(1)/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 degrees 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 Sr2TbRu1-xIrxO6 (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+(Ru1-xIrx)O-5+(6) (x = 0.0-0.7) or Sr2Tb4+(Ru1-xIrx)O-4+(6) (x = 0.85-1.0). Evidence for the presence of a mixed valence state was not found. The magnetic transition temperature for Sr2Tb3+(Ru1-xIrx)O-5+(6) decreases with increasing x. On the other hand, that for Sr2Tb4+(Ru1-xIrx)O-4+(6) increases with x.