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The hyperfine field in Mnl-,Zn, Fe,O, ferrites is studied in dependence on x and temperature. A six:nearest-neighbours model used in evaluating the Mossbauer spectra leads to convex magnetization functions if the number of Zn nearest neighbours is > 3. Das Hyperfeinfeld in Mnl-an, Fe,O,-Ferriten wurde in Abhlingigkeit von x und der Temperatur untersucht. Fur die Auswertung der MoDbauerspektren wurde ein Modell mit sechs nachsten Nachbarn benutzt, das eine konvexe Magnetisierungsfunktion liefert, w enn die Zahl der nachsten Zn-Nachbarn groBer als 3 ist. I ) On leave from the Institute of Nuclear Physics, Cracow. 2, On leave from the A1 Azhar University, Cairo. 9 . 132 L. CSER et, al.

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With the increase of frequencies in microwave communications lithium ferrite single crystals attract growing interest.The characteristic crystal defects of a flux-grown LiF%0 s single crystal were investigated by means of light microscopy, scanning electron microscopy and X-ray topography with respect to the technology. At the beginning of the growth process crystal grains with slightly different orientations and with boundaries containing dislocation groups were forme& Thermal stresses caused cracks. The curved cracks were accompanied by strain fields of helices partly decorated by preeipitates visible on the topographs and also by light microscope. Far from the nucleation site of the crystal large perfect regions containing only straight small-angle boundaries cou]d be found. Precipitates, presumably of LiFeO~, were present in all parts of the crystal. Dislocation arrangements characteristic of stacking faults also appeared on the crystal.

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