Exchange interactions of the chromium spinel oxide HgCr2O4 in high magnetic fields examined by the magnetoelastic theory

The chromium spinel oxide HgCr₂O₄is known to show a peculiar 1/2-plateau in its magnetization curve. The appearance of the magnetization plateau has been interpreted by classical theories, which take into account the magnetoelastic interaction. In this study, we suggest that not only the magnetization curve but also the change in the exchange interaction, which occurs due to lattice distortions during the magnetization process, can be calculated based on the magnetoelastic theory, proposed by Penc et al. We show that the field dependence of the magnetization and the exchange constants, obtained from our previous experiments, agree well with those calculated by the magnetoelastic theory, except for the behaviors prior to the fully polarized phase. This result indicates that an unexpected phase exists just before the saturation of the magnetization in this compound.