No abstract

The cation distribution of MnxZn1−xFe2O4 (x = 0, 0.1, 0.2, 0.4, 0.6, 0.8, 0.9, 1.0) has been determined by neutron diffraction. The fraction of the Mn2+ ions in the tetrahedral sites is correlated to the variation of the lattice parameter with x. It is concluded from the measurements that zinc ferrite is a completely normal spinel and that the Mn2+ ions only occupy the tetrahedral sites up to x = 0.6.

The grain growth and densification rates of Mn‐Zn ferrites during sintering are closely linked to the characteristics of the calcined and milled powders used. Long milling times enlarge powder particle size distributions and tend to promote discontinuous grain growth during sintering. For fixed sintering conditions, an optimum milling time, which corresponds to minimal eddy current and hysteresis losses, exists. The electrical properties of overmilled powders deteriorate greatly because duplex structure occurs. Theoretical analysis of the probability of discontinuous grain growth occurring during sintering in relation to powder particle size distribution agrees with the experimental results.

The temperature dependence of the two sublattices magnetisations of Mn,,,Zn,,,Fe,O, was determined in order to study the superexchange interactions in Mn2+-02+-Fe3+ linkages. The tetrahedral and octahedradl sublattices magnetisations were obtained in absolute scale by neutron diffractometry. Moreover by Mossbauer spectrometry the octahedral sublattice magnetisation was determined in a relative scale as il function of temperature. The results obtained by both methods show the same temperature dependences within the experimental accuracy. The Mossbauer spectra recorded a t temperatures higher than 100 O K show line broadening and overlapping indicating relaxation effects. The molecular field parameters were deduced from the experimental results on the basis of the N6el model. The best agreement is found for JAA = 0, JAB = (-19 f 1) OK, and JBB = (4.7 2) "K. The failing B moment and the evidence for a positive B-B interaction are discussed. Zum Studium des Superaustausches in Mn2+-02+-Fe3+-Zweigen haben wir die Temperaturabhangigkeiten der spontanenMagnetisierungen der beiden Untergitter des kubischen Ferrites Mn,,,Zn,,,Fe,O, bestimmt. Durch Neutronenbeugungsmessungen erhielten wir die Magnetisierungen der Tetraeder-und Oktaederuntergitter in absoluter Skalierung. Mit Hilfe des Mossbauereffektes haben wir die Magnetisierung des Oktaederuntergitters gemessen. Beide Methoden liefern iibereinstimmende Ergebnisse. Die Mossbauerspektren zeigen bei hoheren Temperaturen Linienverbreiterungen, die durch Spinflip-Prozesse gedeutet werden. Die Temperaturverlaufe der Untergittermagnetisierungen lassen sich durch eine Molekularfeldberechnung (NBelsches Modell) mit den Austauschparametern J A A = 0, JAB = (-19 5 1) O K und JBB = (4,7 & 2) "K beschreiben.

It is shown by neutron diffraction and Mössbauer spectrometry that the formation of a long range magnetic order in zinc ferrite depends sensitivily on the content of divalent iron. The experimental data favour a non collinear model of the magnetic structure