  The inverse spinels CoFe2O4 and NiFe2O4, which have been of particular
interest over the past few years as building blocks of artificial multiferroic
heterostructures and as possible spin-filter materials, are investigated by
means of density functional theory calculations. We address the effect of
epitaxial strain on the magneto-crystalline anisotropy and show that, in
agreement with experimental observations, tensile strain favors perpendicular
anisotropy, whereas compressive strain favors in-plane orientation of the
magnetization. Our calculated magnetostriction constants $\lambda_{100}$ of
about -220 ppm for CoFe2O4 and -45 ppm for NiFe2O4 agree well with available
experimental data. We analyze the effect of different cation arrangements used
to represent the inverse spinel structure and show that both LSDA+U and GGA+U
allow for a good quantitative description of these materials. Our results open
the way for further computational investigations of spinel ferrites.
