Rare earth substituted hexagonal m-type ferrites

In this project it shall be tried to produce rare earth substituted ferrites with the goal to find new ferrites with improved magnetic properties. Therefore an all these samples the intrinsic and extrinsic magnetic properties are studied using all an the institute available systems. Sample methodology: Initially sets of new compounds - as the rare earth based ferrites - shall be produced by conventional technologies Suchas mechanical alloying. However, new production techniques yielding thin films or methods leading to nanocrystalline materials are considered as well. In a first attempt improved new ferrites were produced containing La and Co. Thus, it is additionally important to study the related patent compounds like RFe12019 and RCo12019 (R = La,....). In fact, an improvement of the anisotropy (at low temperatures) was first found in pure LaFe12019. Unfortunately, due to limited stability this compound is difficult to produce. Onlyjust recently, SrFe12019 type ferrites doped with rare earth elements could be prepared by means of chemical methods. Thus, the investigation of RFe12019 (R ... rare earth element), where La is replaced also by other rare earth elements, will be an essential part of the project, since the knowledge of the rare earth influence is required for a fundamental understanding of the bulk magnetic properties. The Substitution of Sr(Ba) by a rare earth element with high local magnetic moments is anticipated to significantly increase the magnetic properties. Especially, the large orbital contribution may enhance the magnetocrystalline anisotropy or provide materials with a high magnetostriction. Here, the essential question about the magnetic order of the R - sublattice has to be solved. In analogy to the Sr(Ba) ferrites the effect of substituting Co for Fe is intended to be investigated, too. If a reliable production method is developed it will be tried to produce also nanocrystalline material in order to be able to investigate exchange effects. Experimental methods: The key for a deeper understanding of ferrites, especially the new type of rare earth containing ones, is to investigate the bulk magnetic properties - as e.g. hysteresis, magnetocrystalline anisotropy and magnetostriction. The hysteresis loop will be measured between 4.2K up to the ordering temperature. In selected materials the magnetization process is intended to be studied, too. From the temperature dependence of the anisotropy and the magnetostriction hints can be obtained about the origin of these properties. Additionally local probe methods such as Mössbauer and NMR spectroscopy shall be used.