In the field of magnetic field mapping or imaging, different methods exist making it possible to characterise or visualise magnetic fields.
A first known method of characterisation of magnetic materials, making it possible to visualise the magnetic domains of the magnetic materials, is based on Kerr or Faraday magneto-optic effects. Such a type of characterisation of magnetic materials is described in the following document D1: Anjan Barman, T. Kimura, Y. Otani, Y. Fukuma, K. Akahane et al., “Benchtop time-resolved magneto-optical Kerr magnetometer”, Rev. Sci. Instrum. 79, 123905 (2008). The Kerr effect consists in studying the modifications in reflection of light polarised by a magnetic material and the Faraday effect consists in studying the modifications in transmission of light polarised by a magnetic material. The contrast of the imaging is linked to the orientation of the magnetisation in the material. These two effects can also enable, in certain experiments, the visualisation of external magnetic fields, which act on the magnetisation of the sample. They can in this way give a form of image of the ambient magnetic field. But these effects are indirect and require the lighting of the magnetic sample by polarised light, the images of the magnetic domains being visualised by measuring the rotation of the polarisation of light, translating the orientation of the magnetisation. The study of magnetic fields by these methods requires a costly and cumbersome optical assembly with analyser and polariser.
Another known method also making it possible to optically visualise information on the intensity and the direction of magnetic fields applied in space is the use of ferrofluid materials as described in the following document D2: A Siblini, J Monin, G Noyel and O Brevet-Philibert, “An AC magnetic field remote sensor using a ferrofluid material: application to the measurement of off-centring sleeves of HV transmission lines”, Meas. Sci. Technol. 3 1068 (1992). In this document, magnetic particles dispersed in colloidal solution in a fluid are used. The magnetic field is visualised by the masses of magnetic particles, which move, group together, and agglomerate towards zones of higher gradients of magnetic fields and stronger fields. It is their distributions and concentrations in space that provide information on the magnetic field to observe and form a mapping of the field lines. This method has the drawback of requiring the not very practical use of ferrofluid or powder materials, not reusable because often non-reversible. In addition, these materials generally have a low magnetic susceptibility.
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