  The effect of epitaxial strain on the cation distribution in spinel ferrites
CoFe2O4 and NiFe2O4 is investigated by GGA+U total energy calculations. We
obtain a very strong (moderate) tendency for cation inversion in NiFe2O4
(CoFe2O4), in agreement with experimental bulk studies. This preference for the
inverse spinel structure is reduced by tensile epitaxial strain, which can lead
to strong sensitivity of the cation distribution on specific growth conditions
in thin films. Furthermore, we obtain significant energy differences between
different cation arrangements with the same degree of inversion, providing
further evidence for recently proposed short range B site order in NiFe2O4.
