Researchers have used synchrotron light to detect and record complex 3D magnetisation in wound magnetic layers.
According to the international team, this technique could be important in the development of devices that are highly sensitive to magnetic fields, such as in medical diagnostics for example. Their results are published in Nature Communications.
Three-dimensional structures in materials and biological samples can be investigated using X-ray tomography, which is done by recording images layer-by-layer and assembling them on a computer into a three-dimensional mapping.
To date, there has been no comparable technique for imaging 3D magnetic structures on nanometre length scales. Now teams from Helmholtz-Zentrum Berlin for Materials and Energy (HZB) and the Institute of Solid State Physics, Berlin/Dresden University of Technology in collaboration with research partners from Advanced Light Source/Lawrence Berkeley National Laboratory, and UC Santa Cruz have developed a technique with which this is possible.
They studied the magnetisation in rolled-up tubular magnetic nanomembranes (nickel or cobalt-palladium) about two layers thick. To obtain a 3D mapping of the magnetisation in the tubes, the samples were illuminated with circularly polarised X-rays. Using the X-ray microscope at the Advanced Light Source and the X-ray Photoemission Electron Microscopy (XPEEM) beamline at HZB’s BESSY II, the samples were slightly rotated for each new image so that a series of 2D images was created.
“The polarised light penetrated the magnetic layers from different angles. Using XPEEM, we were not only able to measure the magnetic features at the surface, but also obtained additional information from the “shadow”, said Florian Kronast, who is responsible for the XPEEM beamline at HZB.
The physicists then successfully reconstructed the magnetic features on a computer in three dimensions.
“These samples displayed structures not smaller than 75nm. But with this method we should be able to see even smaller structures and obtain a resolution of 20nm,” Kronast said in a statement. However, so far only electron holography could be considered for mapping magnetic domains of three-dimensional objects at the nanometre scale, a process requiring complex sample preparation. Furthermore, the magnetisation could only be indirectly determined through the resulting distribution of the magnetic field.
“Our process enables you to map the magnetisation in directly in 3D. Knowledge of the magnetisation is prerequisite for improving the sensitivity of magnetic field detectors,” said Kronast.
The new method could be of interest to anyone involved with extremely small magnetic features within small volumes, such as those developing more sensitive devices for medical imaging as procedures – including magnetoencephalography – depend on externally detecting very weak magnetic fields created by the electrical activity of individual nerve cells.