Friday May 25, 2018
Visualizing dynamic magnetism in nanostructures using electron microscopy
By: Trevor P. Almeida, SUPA, School of Physics and Astronomy, University of Glasgow, UK
LOCATION: UAntwerpen, Room U.408
Groenenborgerlaan 171, 2020 Antwerp
In order to better understand chemical phase transformations or magnetic behavior in naturally occurring or synthetic samples, it is often necessary to investigate the underlying processes on the nano-scale. Transmission electron microscopy (TEM) allows atomic spatial resolution imaging and the development of in situ TEM experiments over recent years has provided fundamental insight into a range of dynamic processes. Further, combining in situ TEM experiments with techniques like electron holography or differential phase contrast imaging allows for visualizing of magnetization in nanostructures whilst under the influence of external stimuli; e.g. controlled atmospheres, temperature, etc. In this context, some examples of the use of in situ TEM and magnetic imaging will be presented.
Fe3O4 is the most magnetic naturally occurring mineral on Earth, carrying the dominant magnetic signature in rocks and providing a critical tool in paleomagnetism. The oxidation of Fe3O4 to maghemite (γ-Fe2O3) is of particular interest as it influences the preservation of remanence of the Earth's magnetic field by Fe3O4. Further, the thermomagnetic behavior of Fe3O4 grains directly affects the reliability of magnetic signal recorded by rocks. Through combining electron holography with environmental TEM and in situ heating, the effects of oxidation and temperature on the magnetic behavior of vortex-state Fe3O4 NPs are visualized successfully, for the first time.
Equiatomic iron-rhodium (FeRh) has attracted much interest due to its magnetostructural transition from its antiferromagnetic to ferromagnetic phase. The co-existing phases are separated by a phase-boundary domain wall (DW) and effective control over the creation and motion of these phase boundary DWs are considered desirable for potential application in a new generation of novel nanomagnetic or spintronic devices. In this context, several scanning TEM techniques are performed to visualize the localized chemical, structural and magnetic properties of a series of FeRh films.