Synthesis and antiferromagnetism of Mn5O8.

By reacting manganese nitrate and sodium hydroxide at pH similar or equal t o 12 and heating the product at 400 degreesC for 3 hrs, Mn5O8 with crystall ite size similar or equal to 14 nm and the Cd2Mn5O8 structure is produced, as confirmed by x-ray diffraction. Magnetic state of Mn5O8 is investigated by measuring the temperature variations of the magnetic susceptibility chi and the electron spin resonance spectra. The chi versus T variation is char acteristic of antiferromagnetic ordering with Neel temperature T-N similar or equal to 128 K. For T > T-N, chi follows the Curie-Weiss law, chi = C/(T - theta), with C = 14.26 cm(3)-K/mole, and theta = -164 K. In ESR, only a single line is observed whose linewidth DeltaH fits the variation DeltaH(Oe ) = 1570 + A/(T - T-N)(-gamma) with gamma = 1.26, characteristic of a uniax ial antiferromagnet. The magnitude of C is consistent with the Mn22+Mn34+O8 valence state of Mn5O8.