Ferromagnetism vs. antiferromagnetism of the dimorphic HoCrO4 oxide

This paper reports the specific conditions used in the preparation of the dimorphic phases of HoCrO4 oxide. The scheelite form has been obtained from the room pressure stable HoCrO4–zircon heated at 823 K at 40 kbar. The structures of both the polytypes have been refined from X-ray powder diffraction data using the Rietveld method. The zircon type of HoCrO4 oxide crystallizes with tetragonal symmetry, S.G. I41/amd and lattice parameters a = 7.119(10) and c = 6.2557(5) Å; while the scheelite–HoCrO4 derivative shows tetragonal symmetry, S.G. I41/a and lattice parameters a = 5.0017(1) and c = 11.2664(2) Å. Magnetic susceptibility measurements show that both zircon and scheelite forms of HoCrO4 oxide present a very different magnetic behaviour at low temperatures. The zircon form behaves as a ferromagnet with a Curie temperature of 17.6 K, while the scheelite form is antiferromagnetic with a Néel temperature of 7.6 K. A metamagnetic transition for the scheelite form with a critical field of 1 T at 2 K has been also observed. The changes in the sign of the interactions have been also analyzed by considering the possible super-exchange mechanisms and the differences found in the Ho–O–Cr distances and bond angles in going from zircon to scheelite structural type.

Graphical abstractThe scheelite-type structure of the new HoCrO4 oxide.Figure optionsDownload full-size imageDownload as PowerPoint slide