Crystallography of the Hexagonal Ferrites

摘要: The hexagonal ferrites form an unusual group of complex, ferrimagnetic oxides embodying some 60 known crystal structures. These include phases for which the structural unit cell is larger than that in any inorganic materials. various ferrite modifications fall into two distinct series, each formed by ordered interlayering (stacking) discrete building blocks; these blocks stack along c crystallographic axis varying ratios and permutations to strictly coherent, reproducible This mixed-layering aspect permits direct, visual observation sequence their subunit-cell stacking elements, after etching, means electron microscopy. stacked such structures constitutes only information lacking a complete, three-dimensional structure determination. Direct access this provides immediate, unique solution problem case thereby avoids dilemmas classical diffraction approach large cells. Ferrite with dimensions 1455 1577 angstroms have been uniquely solved direct microscopic readout surface etch features. One must exercise caution, however, generalizing findings other method successful because are mixed-layer structures, wherein react at different rates specific etchant. Mixed-layer systems not uncommon crystallography, it likely similar techniques can be developed Regardless validity prognosis, quite evident high-resolution replica microscopy most promising tool on ultramicro scale. During studies reported here resolution capability was improved about 10 angstroms; final limited particle size platinum shadowing material. Careful control experimental conditions during preparation or alternate choice material, both, might reasonably improve factor 2. within range approaches interatomic distances solid-state potential needs no elaboration.