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Seminar | Materials Science Division

Visualizing Dynamic Magnetic Events on the Nanoscale Using Lorentz Microscopy

MSD Seminar

Abstract: To better understand magnetic behavior in naturally occurring or synthetic samples, it is often necessary to investigate the underlying processes on the nanoscale. Transmission electron microscopy (TEM) allows atomic spatial resolution imaging. and combining in situ TEM experiments with techniques such as electron holography or differential phase contrast (DPC) imaging allows for imaging of magnetization in nanostructures while under the influence of external stimuli (e.g., gas atmospheres, biasing, temperature). In this context, several 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 palaeomagnetism. The oxidation of Fe3O4 to maghemite (γ-Fe3O3) 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 the magnetic signal recorded by rocks. By combining electron holography with environmental TEM, in situ heating, and liquid cell TEM, the effects of oxidation and temperature on the magnetic behavior of Fe3O4 NPs are visualized successfully, as is the magnetism within hydrated magnetotactic bacteria.

Equiatomic iron-rhodium (FeRh) has attracted much interest due to its magnetostructural transition from antiferromagnetic (AF) to ferromagnetic (FM) phase and is considered desirable for potential application in a new generation of novel nanomagnetic or spintronic devices. Several scanning TEM techniques are performed to visualize the localized chemical, structural, and magnetic properties of a series of FeRh films. The quantitative evolution of the growth and co-existence of AF and FM phases in the FeRh films are observed directly during in situ heating using DPC imaging.

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