The Collinear Magnetic Phases of the Geometrically-Frustrated   Antiferromagnet CuFeO$_2$: The Importance of Stacking
  The correct stacking of hexagonal layers is used to obtain accurate estimates for the exchange and anisotropy parameters of the geometrically-frustrated antiferromagnet CuFeO$_2$. Those parameters are highly constrained by the stability of a collinear metamagnetic phase between fields of 13.5 and 20 T. Constrained fits of the spin-wave frequencies of the collinear $\uudd $ phase below 7 T are used to identify the magnetic unit cell of the metamagnetic $\uuudd $ phase, which contains two hexagonal layers and 10 Fe$^{3+}$ spins. 
R.S. Fishman, F. Ye, J.A. Fernandez-Baca, J.T. Haraldsen, and T.   Kimura