Synthesis and antiferromagnetism of Mn5O8

By reacting manganese nitrate and sodium hydroxide at pH≃12 and heating the product at 400°C for 3 hrs, Mn₅O₈ with crystallite size ≃14 nm and the Cd₂Mn₅ O₈ structure is produced, as confirmed by x-ray diffraction. Magnetic state of Mn₅O₈ is investigated by measuring the temperature variations of the magnetic susceptibility χ and the electron spin resonance spectra. The χ versus T variation is characteristic of antiferromagnetic ordering with Neel temperature T_N≃128 K. For T>T_N, χ follows the Curie-Weiss law, χ=C/(T-θ), with C=14.26 cm³ -W/mole, and θ=-164 K. In ESR, only a single line is observed whose linewidth ΔH fits the variation ΔH(Oe)=1570+A/(T-T_N)^-γ with γ=1.26, characteristic of a uniaxial antiferromagnet. The magnitude of C is consistent with the Mn₂²⁺Mn₃⁴⁺O₈ valence state of Mn₅O₈