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.