Hybridized orbital states in spin-orbit coupled 3d-5d double perovskites studied by x-ray absorption spectroscopy

We investigated the orbital hybridization mechanism in 3d-5d double perovskites (DPs) of La2CoIrO6 and La2CoPtO6 using x-ray absorption spectroscopy. It is clearly evidenced by O K-edge and Co K-edge x-ray absorption spectra that the Co 3d orbitals hybridize not only with the half-filled Ir/Pt jeff states but also with the fully empty (unpolarized) Ir/Pt eg states in both DPs. The Co 3d eg-Ir 5d eg hybridization cannot contribute to the ferrimagnetic long-range order in La2CoIrO6 established by spin-selective Co 3d t2g-Ir 5d jeff hybridization through the intermediate oxygen p state but could serve as an origin of paramagnetism. The strengths of such orbital hybridizations were found to be almost invariant to temperature, even far above the Curie temperature, implying persistent paramagnetism against the antiferromagnetic ordering in the spin-orbit entangled 3d-5d DPs.