Slow Magnetic Order-Order Transition in the Spin Chain Antiferromagnet   Ca3Co2O6
  Using powder neutron diffraction we have discovered an unusual magnetic order-order transition in the Ising spin chain compound Ca3Co2O6. On lowering the temperature an antiferromagnetic phase with propagation vector k=(0.5,-0.5,1) emerges from a higher temperature spin density wave structure with k=(0, 0, 1.01). This transition occurs over an unprecedented time-scale of several hours and is never complete. 
S. Agrestini, C.L. Fleck, L.C. Chapon, C. Mazzoli, A. Bombardi, M.R.   Lees, O.A. Petrenko
cond-mat.str-el cond-mat.mtrl-sci