Exsolution microstructures in titanomagnetites and their magnetic significance

A survey, carried out using transmission electron microscopy, of exsolution-derived microstructures developed in titanomagnetites is presented. Microstructures, probably produced by spinodal decomposition, consist of a three-dimensional lamellar framework of ulvospinel, separating magnetite-enriched blocks. In coarser textures the magnetite-enriched regions have a plate morphology, and the ulvospinel-enriched lamellae develop secondary exsolution textures. The implications of exsolution for the magnetic properties of titanomagnetites are discussed. The coarsening of exsolution textures will cause the blocking temperature of the magnetite-enriched regions to increase with time. The development of magnetite-enriched plates may alter the magnetic properties of the titanomagnetite, as may the stress associated with some of the small scale, coherent microstructures.