3d and 5d electronic structures and orbital hybridization in Ba- and Ca-doped La₂CoIrO₆ double perovskites

Here we present a detailed investigation of the Co and Ir local electronic structures in La1.5A0.5CoIrO6 (A = Ba, Ca) compounds in order to unravel the orbital hybridization mechanism in these CoIr-based double perovskites. Our results of x-ray powder diffraction, ac and dc magnetization, Co and Ir L2,3-edge and Co K-edge x-ray absorption spectroscopy and x-ray magnetic circular dichroism suggest a competition between magnetic interactions. A dominant antiferromagnetic coupling is found to be responsible for the ferrimagnetic behavior observed for A = Ca below & SIM;96 K, the competing magnetic phases, and the cationic disorder in this compound giving rise to a spin-glass state at low temperatures. For the A = Ba, on the other hand, there is no evidence of long-range order down to its spin-glass transition temperature. The remarkably different magnetic properties observed between these two compounds are discussed in terms of the structural distortion that alters the strength of the Co-Ir couplings, with a relevant role played by the Co 3d eg-Ir 5d jeff = 1/2 hybridization.