Antisite Defect and Magnetic Frustration in Double Perovskite Ln 2 CuRuO 6 (Ln = La, Pr) Compounds

Magnetism in double perovskite oxides of the formula A2BB'O6 has been a subject of great interest and intensive research in condensed matter physics. In this paper, Ln2CuRuO6 (A = La, Pr) samples were synthesized by solid-state reaction method, and we investigated their structural and magnetic properties. The new double perovskite compound Pr2CuRuO6 stabilizes in the monoclinic P21/n structure with an antisite defect fraction of ~ 3% between Cu and Ru sites. Our structural analysis indicates the severe deformation of Cu-O-Ru bond angle, as La3+ is replaced by the smaller rare earth ion Pr3+. For Pr2CuRuO6, the observed ferromagnetic transition temperature (Tc = 32 K) is higher than that of La2CuRuO6 (Tc = 15 K), which may be possibly associated with the enhanced magnetic interaction due to the distorted Cu-O-Ru bond angle. In addition, the anomalous phenomenon of ZFC susceptibility at low temperature suggests a degree of magnetic frustration and can be attributable to the intrinsic antisite defect in Pr2CuRuO6. The first principle calculations confirm a ferromagnetic Cu-Ru exchange interaction in Pr2CuRuO6, which is different from the antiferromagnetic case for La2CuRuO6.