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

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Abstract
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 momentMc 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 .

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