X-Ray and Neutron Diffraction Studies in Spinel Fe₂MoO₄

Stoichiometric sample of Fe ₂ MoO ₄ was prepared in a controlled atmosphere of CO ₂ -H ₂ mixed gas at 1140°C (log P o ₂ - P o ₂ ∼-12.5). The crystal structure and the cation distribution were determined from, X-ray and neutron diffraction measurements on the powdered samples. Fe ₂ MoO ₄ is a completely inverse spinel; the parameters are given as a =8.509 Å and u =0.383±0.003. The compound shows a week spontaneous magnetization (0.15∼0.2 µ _B /mol) below 348 K (Néel point), and the spontaneous magnetization changes sign at about 160 K (compensation point). The magnetic structure was determined to be Néel type like Fe ²⁺ (4\(\overrightarrow{\mu}_{\text{B}}\)) [Fe ²⁺ (4\(\overleftarrow{\mu}_{\text{B}}\))Mo ⁴⁺ (0µ _B )]0 ₄ , where (4d) ² electrons of Mo ⁴⁺ ion are in low spin state, and the origin of the weak spontaneous magnetization is attributed to the uncompensation and/or canting of spins of Fe ₂₊ ions on the A and B sites of the spinel lattice.