Synthesis and Antiferromagnetism of [Mn.sub.5][O.sub.8]

By reacting manganese nitrate and sodium hydroxide at pH [nearly equal to] 12 and heating the product at 400 [degrees] C for 3 hrs, [Mn.sub.5][O.sub.8] with crystallite size [nearly equal to] 14 nm and the [Cd.sub.2][Mn.sub.5][O.sub.8] structure is produced, as confirmed by x-ray diffraction. Magnetic state of [Mn.sub.5][O.sub.8] is investigated by measuring the temperature variations of the magnetic susceptibility [Chi] and the electron spin resonance spectra. The [Chi] versus T variation is characteristic of antiferromagnetic ordering with Neel temperature [T.sub.N] [nearly equal to] 128 K. For T [is greater than] [T.sub.N], [Chi] follows the Curie-Weiss law, [Chi] = C/(T - [Theta]), with C = 14.26 [cm.sup.13]-K/mole, and [Theta] = -164 K. In ESR, only a single line is observed whose linewidth [Delta]H fits the variation [Delta]H(Oe) = 1570 + A/[(T - [T.sub.N]).sup.[Gamma] with [Gamma] = 1.26, characteristic of a uniaxial antiferromagnet. The magnitude of C is consistent with the [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] valence state of [Mn.sub.5][O.sub.8]. Index Terms--Antiferromagnetism, electron spin resonance, mixed valences, synthesis.