2892.     ROQUET, J.  [Magnetic Properties of Magnetic Ferric Oxide.]  Compt. rend., vol. 222, 1946, pp. 727-729; British Abs., 1946, I, A, p. 274.

        Fe₂O₃ was heated to 700° and cooled in a magnetic field.  Its specific permanent magnetization, σ, was measured.  The Fe₂O₃ was heated again to 700°, which demagnetized it, and it was allowed to cool again in the same field.  There was an increase in σ after each heating and cooling.  The curve of σ against time t (the sum of the individual times during which the Fe₂O₃ was heated to 700°) tends toward a limit, σ₃, for t amounting to several days.  X-ray analysis reveals no change in the crystalline structure, σ, and the time required to attain it vary considerably from one sample to another.  The susceptibility of the unheated Fe₂O₃ is 100X10^-6-200X10^-6. If X₄ is the susceptibility after a short period of heating and X₃ is that after heating long enough for the magnetization to reach the limit, X₄ does not differ from X₃ for a given sample by more than the experimental error and lies between 25X10^-6 and 32X10^-6.