Observation of a c‐Axis Moment in α‐Fe2 O3

The Dzyaloshinsky theory for spin configurations in the rhombohedral weak ferromagnet α‐Fe2O3 predicts above the Morin transition temperature a very small c‐axis magnetic moment Mc having a threefold symmetry. This property has been experimentally observed for the first time using a rotating sample magnetometer. Mc is found to vary as AMs cos3Ψ when a saturating field rotates through an angle Ψ in the basal plane, being equal to zero when the field is along any of the three twofold axes. For 11 α‐Fe2O3 crystals the average value of A is 1.15±0.4×10−3 with Ms equal to the weak spontaneous moment in the basal plane. Since a canting angle for the spins in the basal plane of 10−4 rad will produce Ms, a spin canting toward c of only 10−7 rad can account for Mc.