Structure, Magnetism, and Valence States of Cobalt and Platinum in Quasi-One-Dimensional Oxides A3CoPtO6 with A = Ca, Sr

Two quasi-one-dimensional oxides, Ca3CoPtO6 and Sr3CoPtO6, were synthesized and characterized. A combination of X-ray absorption spectroscopy at the Co-K-, Co-L2,3-, and Pt-L3-edges and X-ray photoelectron spectroscopy establishes unambiguously the divalent state of Co and the tetravalent state of Pt in both compounds, in contrast to the earlier assumption of the Co3+ and mixed Pt2+/Pt4+ valence states. Magnetization measurements reveal the paramagnetic behavior down to 2 K with strong evidence for an unquenched orbital moment of the high-spin Co2+. The simple paramagnetic behavior of A3CoPtO6 contrasts with the magnetic transitions observed in Ca3CoRhO6, Sr3CoIrO6, and other isostructural materials. This difference is ascribed to the nonmagnetic 5d6 state of Pt4+ that prevents magnetic couplings between the Co2+ ions.