Valence, spin, and orbital state of Co ions in one-dimensional Ca3Co2O6:: An x-ray absorption and magnetic circular dichroism study

We have investigated the valence, spin, and orbital state of the Co ions in the one-dimensional cobaltate Ca3Co2O6 using x-ray absorption and x-ray magnetic circular dichroism at the Co-L-2,L-3 edges. The Co ions at both the octahedral Co-oct and trigonal Co-trig sites are found to be in a 3+ state. From the analysis of the dichroism we established a low-spin state for the Co-oct and a high-spin state with an anomalously large orbital moment of 1.7 mu(B) at the Co-trig(3+) ions. This large orbital moment along the c-axis chain and the unusually large magnetocrystalline anisotropy can be traced back to the double occupancy of the d(2) orbital in trigonal crystal field.