Neutron Diffraction Determination of Antiferromagnetism in Face-Centered Cubic (γ) Iron

Microcrystalline particles of $\gamma$ iron of nearly identical orientation in a single-crystal copper matrix give a neutron diffraction pattern, in the liquid helium temperature range, consistent with the development of antiferromagnetism. The spin structure resembles that of $\gamma$ manganese, but with the spin vectors inclined at about 19° from the normal to the ferromagnetic sheets. The spin directions in alternate sheets are antiparallel. The moment per iron atom is about 0.7 ${\mathrm{\mu }}_{\mathrm{B}}$ and the Néel temperature, estimated from the Brillouin function temperature dependence of the magnetic intensities, is about 8°K.