X-ray, synchrotron, and neutron powder diffraction techniques were combined to investigate the evolution of crystal structure and physical properties of La 2−x Sr x CoIrO 6 with temperature and composition x. The following sequence of first-and second-order phase transitions is observed in this system, induced by increasing Sr content and temperature:The low-temperature magnetic structures are characterized by the propagation vector k = ͑0,0,0͒ for x =0, k = ͑1 / 2,0,1/ 2͒ for x = 1, and k = ͑0,1/ 2,1/ 2͒ or k = ͑1 / 2,0,1/ 2͒ for 1.5 and 2. Different noncollinear magnetic structures are concluded from the combination of magnetization measurements and neutron powder diffraction. Resistivity measurements reveal that the whole series behaves like nonmetals with electronic transport described by a combination of thermal activation and variable range hopping. Band gaps determined by electronic structure calculations agree very well with the experimental data for x = 0 and 1, and the calculated occupation of the d bands of Co and Ir are in good agreement with a transition IS/ HS-Co 2+ / LS-Ir 4+ → HS-Co 3+ / LS-Ir 5+ with increasing Sr content.

No abstract

We have studied Ir spin and orbital magnetic moments in the double perovskites La2−xSrxCoIrO6 by x-ray magnetic circular dichroism. In La2CoIrO6, Ir 4+ couples antiferromagnetically to the weak ferromagnetic moment of the canted Co 2+ sublattice and shows an unusually large negative total magnetic moment (-0.38 µB/f.u.) combined with strong spin-orbit interaction. In contrast, in Sr2CoIrO6, Ir 5+ has a paramagnetic moment with almost no orbital contribution. A simple kinetic-energy-driven mechanism including spin-orbit coupling explains why Ir is susceptible to the induction of substantial magnetic moments in the double perovskite structure.