Technique for imaging magnetisation dynamics developed in a joint project

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In the future, electronic storage technology may be superseded by devices based on tiny magnetic structures. These individual magnetic regions correspond to bits and need to be as small as possible and capable of rapid switching. In order to better understand the underlying physics and to optimise the components, various techniques can be used to visualise the magnetisation behaviour.

An electron microscope-based technique that makes it possible not only to capture static images of these components but also to film the high-speed switching processes has been developed by scientists at Johannes Gutenberg University Mainz (JGU) in Germany.

JGU has employed a specialised signal processing technology that suppresses image noise. "This provides us with an excellent opportunity to investigate magnetisation in small devices," Daniel Schönke of the JGU Institute of Physics explained.

Scanning electron microscopy with polarisation analysis is a lab-based technique for imaging magnetic structures. Compared with optical methods, the researchers say it has the advantage of high spatial resolution. The main disadvantage is the time it takes to acquire an image in order to achieve a good signal-to-noise ratio. However, the time required to measure the periodically excited, and therefore periodically changing magnetic signal, can be shortened by using a digital phase-sensitive rectifier that only detects signals of the same frequency as the excitation.

Such signal processing requires measurements to be time-resolved. The instrumentation developed by JGU is said to provide a time resolution of better than 2 nanoseconds. As a result, the technique can be employed to investigate high-speed magnetic switching processes. It also makes it possible to both capture images and select individual images at a defined point in time within the entire excitation phase.

According to the researchers, this development means the technique is now comparable with the much more complex imaging techniques used at large accelerator facilities and opens up the possibility of investigating the magnetisation dynamics of small magnetic components in the laboratory.