New insights into the magnetism and magnetic structure of LuCrO perovskite.

A polycrystalline sample LuCrO has been characterized by neutron powder diffraction (NPD) and magnetization measurements. Its crystal structure has been Rietveld refined from NPD data in space group Pnma; this perovskite contains strongly tilted CrO octahedra with extremely bent Cr-O-Cr superexchange angles of ∼142°. The NPD data show that below Néel temperature (T ≃ 131 K), the magnetic structure can be defined as an A-type antiferromagnetic arrangement of Cr magnetic moments, aligned along the b axis, with a canting along the c axis. A noticeable magnetostrictive effect is observed in the unit-cell parameters and volume upon cooling down across T. The AC magnetic susceptibility indicates the onset of magnetic ordering below 112.6 K; the magnetization isotherms below T show a nonlinear behaviour that is associated with the described canting of the Cr magnetic moments. From the Curie-Weiss law, the effective moment of the Cr sublattice is found to be μ = 3.55 μ (calculated 3.7 μ) while the Θ parameter yields a value of -155 K, indicating antiferromagnetic interactions. There is a conspicuous increase of T upon the application of external pressure, which must be due to shortening of the Cr-O bond length under compression that increases the orbital overlap integral.