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 1368.    HAUL, R., AND SCHOON, T.  [Elementary Range of Ferromagnetism.]  Ztschr. Elektrochem., vol. 45, 1939, pp. 663-671; Chem. Abs., vol. 34, 1940, p. 298.

        γ-Fe₂O₃ was prepared by oxidation of Fe pentacarbonyl.  The magnitude of the primary crystals decreases with decreasing reaction temperature until finally preparations are obtained amorphous to X-ray.  When crystal identification by means of X-ray is no longer possible, electron rays are used.  The magnetic susceptibility is measured by the cylinder method with different field strengths.  Up to a range of lattice magnitudes of about 30-40 Å., there is a slight increase in susceptibility, which then rises about 10% to the amount characteristic of ferromagnetic substances.  This experimentally determined value marks the lowest elementary particle at which spontaneous magnetization occurs.