Three-dimensional Crystallographic and Magnetic Microstructures in Rocks

Takeshi Kasama
Staff at DTU Cen: Alice Bastos da Silva Fanta, Marco Beleggia
Funding: DTU Cen
The importance of studying magnetic oxide minerals such as magnetite (Fe3O4)-ulvöspinel (Fe2TiO4) and hematite (Fe2O3)-ilmenite
(FeTiO3) solid solutions, which are distributed widely in the Earth’s surface and crust, results from their ability to retain a natural remanent magnetization over geological time scales, thereby allowing the past geomagnetic field to be reconstructed. Therefore it is important to understand their magnetic properties.Electron holography in the transmission electron microscope (TEM) can be used to study the magnetic fields in nanostructured materials at the nanometer scale and has been successfully applied in many studies. However, for a TEM examination, a specimen has to be thinned down to a few hundreds nm. Such a thinned specimen may not have the same magnetic properties that the bulk material had originally. Here we use a combination of focused ion beam milling and EBSD in the scanning electron microscope (SEM) to characterise the 3D microstructure and local crystallographic orientation of a magnetite/ilmenite intergrowth.

The figure below shows four different crystallographic orientations of an ilmenite phase in a magnetite host, suggesting that ilmenite
and magnetite have a strong crystallographic relationship. The technique also allows us to study the growth process of crystals from
their connectivity, which is difficult to obtain from conventional two-dimensional SEM images.

                 

Three-dimensional reconstruction of ilmenite, showing four different crystallogphic orientations. The data were acquired using the FIB-SEM and FIB-EBSD techniques in DTU Cen’s Helios.The scale bar is 5 μm. 

Takeshi Kasama
Seniorforsker
DTU Cen
45 25 64 75
Alice Bastos da Silva Fanta
Seniorforsker
DTU Cen
45 25 64 69
Marco Beleggia
Lektor
DTU Cen
45 25 31 47