Visualizing Magnetic Domains with the NanoMOKE 3

Visualizing Magnetic Domains with the NanoMOKE 3

The NanoMOKE 3 software LXPro 3 has a function built in to image domains and their switching magnetization called 3D looping. For some of our users this measurement mode was not sufficient to catch the domains mid-switch as it happens very fast.

You can observe the switching in almost live video by following these steps:

  1. Set fields to “manual fields”
  2. Set a saturation field
  3. Start imaging, select “Kerr Rotation” as display
  4. Right-click in the image area and select “Set as background”
  5. Change the field to something that nudges the domains towards switching (e.g. for the out-of-plane test sample that came with the instrument, set a saturation of 300 Oe, then change to -30 Oe to begin switching)
  6. At some point you will see the domain wall moving through the imaging area. If you quickly set the field to 0 Oe you can stop the movement.

Now you could go ahead and take consecutive images of the domain wall motion. This, however, is quite tedious. I came across a section in the manual that talks about an API that can be used to control the software externally. It basically let’s you do (almost) everything you can do on the GUI.

All it needs to work is a folder C:\NanoMOKEInbox and a text file in it, containing the macro commands to be executed. Once the software sees a new file, it begins executing the commands and deletes the file when finished.

Domain Viewer GUI

The above mentioned procedure to image domains can now be automatized in a macro. The text file can then contain consecutive commands to save image files, say, every second while the domains move through the field of view.  I wrote a small Labview  program (“Domain Viewer”) that does just that: creating a text file with parameters chosen on the LabView GUI and copying the file into C:\NanoMOKEInbox.

The macro will create a sequence of .skm3 image files in the designated folder. These image files can then be loaded into the LXPro 3 via “File – Open Image(s)”. Select all image files and click “Open”. Go to the “Imaging” tab and use the slider to move though the sequence of images. Go to “File – Export all images (3D)” and select “as JPG”. This will create .jpg files for each of your .skm3 files that you can then process further.

Animated GIF showing Domains

One can combine the .jpg to create a small animation. There are tons of programs out there for this purpose. The animated GIF shown here was done with ImageJ, a free and open source program designed for scientific image processing. It also allows to crop the finished animated GIF, a very useful feature considering that the image data files created by LXPro 3 also contain undesired elements like the LabView GUI widgets located around the actual image.

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