A new spatial imaging method makes it possible to map a material's magnetic permeability at the microscopic scale, according to work published in Nature. The technique combines high-resolution magnetic measurements with images of the microstructure to show how the local magnetic response varies from one region to another within the same sample.

Magnetic permeability — a material's ability to concentrate and conduct magnetic flux — is usually measured as an average over the whole sample. That average hides internal heterogeneity: domains, grains, defects and secondary phases can have very different responses, and it is precisely this variation that determines the material's functional behaviour in transformers, sensors or magnetic memory.

The described method overcomes this limitation by combining a proximity magnetic sensor with microscopy of the material's crystal structure. By scanning the sample point by point, the team obtains a two-dimensional map of permeability that can be overlaid on the microstructural image, allowing magnetic function to be correlated directly with specific structural features.

The authors highlight that this approach paves the way for designing magnetic materials from their microstructure rather than by trial and error. Next steps include extending the technique to other functional parameters and to more complex materials, as well as applying it to quality control of commercial magnetic devices.