The nature of the magnetic order in Ca3Co2O6
  We present a detailed powder and single crystal neutron diffraction study of the spin chain compound Ca3Co2O6. Below 25 K, the system orders magnetically with a modulated partially disordered antiferromagnetic structure. We give a description of the magnetic interactions in the system which is consistent with this magnetic structure. Our study also reveals that the long-range magnetic order co-exists with a shorter range order with a correlation length scale of 180 A in the ab plane. Remarkably, on cooling, the volume of material exhibiting short range order increases at the expense of the long-range order. 
S. Agrestini, L. C. Chapon, A. Daoud-Aladine, J. Schefer, A. Gukasov,   C. Mazzoli, M. R. Lees, and O. A. Petrenko