Incommensurate magnetic ground state revealed by resonant x-ray scattering in the frustrated spin system Ca3Co2O6

We have performed a resonant x-ray scattering study at the Co pre-K edge on a single crystal of Ca(3)Co(2)O(6). The measurements reveal an abrupt transition to a magnetically ordered state immediately below T(N)=25 K, with a magnetic correlation length in excess of 5500 A along the c axis chains. There is no evidence for modifications to the Co(3+) spin state. A temperature dependent modulation in the magnetic order along the c axis and an unusual decrease in the magnetic correlation lengths on cooling are observed. The results are compatible with the onset of a partially disordered antiferromagnetic structure in Ca(3)Co(2)O(6).