By reacting manganese nitrate and sodium hydroxide at pH/spl sime/12 and heating the product at 400/spl deg/C for 3 hrs, Mn/sub 5/O/sub 8/ with crystallite size /spl sime/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 /spl chi/ and the electron spin resonance spectra. The /spl chi/ versus T variation is characteristic of antiferromagnetic ordering with Neel temperature T/sub N//spl sime/128 K. For T>T/sub N/, /spl chi/ follows the Curie-Weiss law, /spl chi/=C/(T-/spl theta/), with C=14.26 cm/sup 3/-W/mole, and /spl theta/=-164 K. In ESR, only a single line is observed whose linewidth /spl Delta/H fits the variation /spl Delta/H(Oe)=1570+A/(T-T/sub N/)/sup -/spl gamma// with /spl gamma/=1.26, characteristic of a uniaxial antiferromagnet. The magnitude of C is consistent with the Mn/sub 2//sup 2+/Mn/sub 3//sup 4+/O/sub 8/ valence state of Mn/sub 5/O/sub 8/.
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Punnoose et al. (2001) studied this question.
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