Hexagonal ferrites: a unified model of the (TS)_nT series in superspace

Hexagonal ferrites represent an extensive family of mixed-layer magnetic materials with periods up to 1500 Å along the stacking direction, probably constituting the largest unit cells in the inorganic realm. The (TS)_nT subfamily includes and structures that can be derived from Y ferrite Ba₂M₂Fe₁₂O₂₂ (M = Zn, Fe, Co, Mg, Mn) by introducing stacking faults. A unified (3 + 1)-dimensional superspace model is proposed for all members of the (TS)_nT family. The model belongs to the superspace group with , , has a unit cell of the basic structure with a = 5.88, c = 4.84 Å and modulation vector , where n is rational for periodic structures and irrational for the aperiodic ones. The model was tested on calculated data of one of the principal members of the (TS)_nT family, the Y ferrite (). The fit obtained with the superspace model was excellent. The model allowed a reduction of refinable parameters by 19% with respect to the ordinary refinement without a significant increase of the refinement R values.