X ray powder photographs have been taken of samples of the system SrO-Fe2O3 and it is found that at least three phases are present in this system; one of them is of the hexagonal magnetoplumbite structure, which is strongly magnetic. Another one, corresponding to the composition of 0.7 SrO 0.3Fe2O3 is cubic, with its lattice constant equal to 3.86 × n Å, where n is an integer. This is not ferromagnetic at room temperature. The last phase, whose crystallographic symmetry is unknown, occurs at the composition SrOFe2O3. The observed ferromagnetism seems to originate exclusively from the magnetoplumbite structure.
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