Superspace approach applied to the Y series of hexagonal ferrites
Ivan S. Orlov, Alla V. Arakcheeva, G. Chapuis · Acta Crystallographica Section A Foundations of Crystallography · 2004
Hexagonal ferrites, a group of ferromagnetic layered structures with exceptional diversity, is based on six compounds which are closely related to BaFe 12 O 19 (magnetoplumbite) [1].They can all be derived by stacking three building blocks S, R and T, having 2, 3 and 4 oxygen layers respectively.These blocks behave as rigid structural units and stack along the c axis in a variety of ratios and permutations, often rising to structures of 'biological magnitude' [2].We succeeded to describe the structures built by all combinations of T and S blocks by a single structural model in 4-dimensional superspace with single composition-dependent parameter.This model is supported by electron diffraction simulation where the continuously variable character of the diffraction diagram indicates that various stacking sequences might be interpreted as modulations applied to a common basic structure.