Nature of transport gap and magnetic order in zircon and scheelite type DyCrO4 from first principles.

Our first principles density functional theory calculations within GGA + U approximation reveal that the nature of transport gaps in the zircon and scheelite phases of DyCrO(4) are quite different. While in the scheelite phase the origin of the gap is more like that of the Mott-Hubbard systems, in the zircon phase the origin is not strictly a Mott-Hubbard or a charge transfer type. In the framework of the Zaanen-Sawatsky-Allen phase diagram, the DyCrO(4) in its zircon phase could be placed in the intermediate regime between the charge transfer and Mott-Hubbard insulators. On the issue of ground state magnetic order in these two phases, where no consensus exists so far from experimental observations, we have performed GGA and GGA + U calculations on various possible magnetic configurations. We clearly establish from our theoretical calculations that the ferrimagnetic order, where ferromagnetic Dy and Cr sublattice are aligned antiparallel to each other, is the ground state in the zircon phase, while in the scheelite phase competing long-range antiferromagnetic orders are observed. Our estimation of various superexchange interactions indicate that competing ferro- and antiferro-magnetic interactions exist which would explain the experimental observation of metamagnetic transitions on application of a small external magnetic field in these systems.