Intricacies of the Co3+ spin state in Sr2Co0.5Ir0.5O4: An x-ray absorption and magnetic circular dichroism study

We report on a combined soft x-ray absorption and magnetic circular dichroism (XMCD) study at the Co-L-3,L-2 edge on the hybrid 3d/5d solid state oxide Sr2Co0.5Ir0.5O4 with K2NiF4 structure. Our data indicate unambiguously a pure high spin state (S = 2) for the Co3+ (3d(6)) ions with a significant unquenched orbital moment L-z/2S(z) = 0.25 despite the sizable elongation of the CoO6 octahedra. Using quantitative model calculations based on parameters consistent with our spectra, we have investigated the stability of this high spin state with respect to the competing low spin and intermediate spin states.