High and low-temperature crystal and magnetic structures of   epsilon-Fe2O3 and their correlation to its magnetic properties
  The crystal and magnetic structures of the orthorhombic e-Fe2O3 have been studied by simultaneous Rietveld refinement of X-ray and neutron powder diffraction data in combination with Mossbauer spectroscopy, as well as magnetisation and heat capacity measurements. It has been found that above 150 K the e-Fe2O3 polymorph is a collinear ferrimagnet with the magnetic moments directed along the a axis, while the magnetic ordering below 80 K is characterised by a square-wave incommensurate structure. The transformation between these two states is a second order phase transition and involves subtle structural changes mostly affecting the coordination of the tetrahedral and one of the octahedral Fe sites. The temperature dependence of the e-Fe2O3 magnetic properties is discussed in the light of these results. 
M. Gich, C. Frontera, A. Roig, E. Taboada, E. Molins, H. R.   Rechenberg, J. D. Ardisson, W. A. A. Macedo, C. Ritter, V. Har...