Magnetodielectric coupling in Mn3 O4

We have investigated the dielectric anomalies associated with spin-ordering transitions in the tetragonal spinel Mn3 O4 using thermodynamic, magnetic, and dielectric measurements. We find that two of the three magnetic ordering transitions in Mn3 O4 lead to decreases in the temperature-dependent dielectric constant at zero applied field. Applying a magnetic field to the polycrystalline sample leaves these two dielectric anomalies practically unchanged, but leads to an increase in the dielectric constant at the intermediate spin-ordering transition. We discuss possible origins for this magnetodielectric behavior in terms of spin-phonon coupling. Band structure calculations suggest that in its ferrimagnetic state, Mn3 O4 corresponds to a semiconductor with no orbital degeneracy due to strong Jahn-Teller distortion.