#REPEATING A UNIT CELL IN CRYSTALMAKER SERIES#

The best known hexaferrite compounds are those where the divalent M cation is cobalt, however, the hexaferrites described herein contain zinc as the divalent M cation. Besides M-type, the main hexaferrites are Ba M 2Fe 16O 27 (so-called W-type), Ba 2 M 2Fe 12O 22 (Y-type), Ba 3 M 2Fe 24O 41 (Z-type), Ba 2 M 2Fe 28O 46 (X-type) and Ba 4 M 2Fe 36O 60 (U-type), where M = Co 2+, Zn 2+, Fe 2+, Mg 2+, Mn 2+ etc. There are many variations of hexaferrites (Pullar, 2012 ), the most common member being the BaFe 12O 19 M-type hexaferrite, which is well known for its use as a permanent magnet. The hexaferrites are a family of magnetic iron(III)-based oxides with hexagonal, trigonal or rhombohedral crystal structures related to the Pb 12O 19 magnetoplumbite structure type. These materials present a wide variety of applications and are widely used as magnets, magnetic recording or data storage materials and electrical device components (especially those operating at microwave frequencies for antennas, isolators, filters etc.) (Özgür et al., 2009 ). Hexagonal ferrites or so-called hexaferrites, distinct from cubic or spinel ferrites, have been the subject of numerous studies since their discovery in the 1950s and are still extensively investigated for their magnetic and microwave properties (Batlle et al., 1991 Liu et al., 2006 Stergiou & Litsardakis, 2016 ). The structures include a new hexaferrite stacking sequence, with the longest lattice parameter of any hexaferrite with a fully determined structure.

#REPEATING A UNIT CELL IN CRYSTALMAKER SERIES#

This paper describes the growth of a series of complex hexaferrite crystals, their atomic-level structure solution by high-resolution synchrotron X-ray diffraction, electron diffraction and imaging methods, and their physical characterization by magnetometry. This has limited atomic-resolution structure solutions to relatively simple examples such as Ba 2Zn 2Fe 12O 22, whilst longer stacking sequences have been modelled only in terms of block sequences, with no refinement of individual atomic coordinates or occupancies. Their crystal structures are highly modular, consisting of Fe- or Ba-rich close-packed blocks that can be stacked in different sequences to form a multitude of unique structures, producing large anisotropic unit cells with lattice parameters typically >100 Å along the stacking axis. Hexaferrites are an important class of magnetic oxides with applications in data storage and electronics.

Repeating a unit cell in crystalmaker