Synthesis and magnetic properties of the high-pressure scheelite-type GdCrO4 polymorph

The scheelite-type polymorph of GdCrO4 has been obtained from the corresponding zircon-type compound under high pressure and temperature conditions, namely 4 GPa and 803 K. The crystal structure has been determined by X-ray powder diffraction. This GdCrO4 scheelite crystallizes in a tetragonal symmetry with space group I41/a (No. 88, Z=4), a=5.0501(1) Å, c=11.4533(2) Å and V=292.099(7) Å3. The thermal decomposition leads to the formation of the zircon–polymorph as intermediate phase at 773 K to end in the corresponding GdCrO3 distorted perovskite-structure at higher temperatures. Magnetic susceptibility and magnetization measurements suggest the existence of long-range antiferromagnetic interactions which have been also confirmed from specific heat measurements. Neutron powder diffraction data reveal the simultaneous antiferromagnetic Gd3+ and Cr5+ ordering in the scheelite-type GdCrO4 with a TN∼20 K. The magnetic propagation vector was found to be k=(0 0 0). Combined with group theory analysis, the best neutron powder diffraction fit was obtained with a collinear antiferromagnetic coupling in which the mCr5+mCr5+ and mGd3+mGd3+ magnetic moments are confined in the tetragonal basal plane according to the mixed representation Γ6 ⊕ Γ8.

graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideThermal decomposition of the GdCrO4 high pressure polymorph, from the scheelite-type through the zircon-type structure as intermediate to end in the GdCrO3 perovskite.Highlights► New high pressure GdCrO4 polymorph crystallizing in the scheelite type structure. ► It is an antiferromagnet with a metamagnetic transition at low magnetic fields. ► We have determined its magnetic structure from powder neutron diffraction data. ► Otherwise, the room pressure zircon–polymorph is a ferromagnet. ► The paper will be a great contribution in the study of 3d–4f magnetic interactions.