High- and low-temperature crystal and magnetic structures of ε-Fe2O3 and their correlation to its magnetic properties

The crystal and magnetic structures of orthorhombic epsilon-Fe2O3 have been studied by simultaneous Rietveld refinement of X-ray and neutron powder-diffraction data in combination with Mossbauer spectroscopy, as well as magnetization and heat-capacity measurements. It has been found that above 150 K, the epsilon-Fe2O3 polymorph is a collinear ferrimagnet with magnetic moments directed along the a axis, whereas the magnetic ordering below 80 K is characterized 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 epsilon-Fe2O3 magnetic properties is discussed in light of these results.