The SNOM (Scanning Near-field Optical Microscopy) allows to reach a spatial resolution well below the wavelength of the light used. Indeed, thanks to the "near-field" illumination (when the distance between the object and the source is much less than the wavelength) it becomes possible to avoid the diffraction inherent to every optical system. Measurement of the evanescent field at the back side of a total-reflection interface allows obtaining a SNOM image with a resolution well below one micrometer.
Multi-ferroïcs are exceptional materials whose fundamental state is both magnetic and ferro-electric . Moreover, in such materials, magnetism and ferroelectricity maintains close links: as for example the manganese oxide YMnO3 , can see its magnetization modified by the action of an electric field, or its electric polarization by the action of a magnetic field (magnetoelectric effect). Muli-ferroïcity is a complex problem in physics of condensed matter; it also represents an important stake for the applications, and for example for “technologies for the information and health” developed at the CEA (development of new concepts of memorizing the information or spin electronics).
The last research on these materials tends to show that the coupling between magnetism and ferro-electricity occurs via important deformations of the crystal lattice. It is known for example that in the case of the compound YMnO3, the transition (TN = 72K) towards the magnetic phase (and thus multi-ferroïc) is the seat of magnetostrictive effects that reveals the strong coupling between atomic displacements, magnetic ferroelectricity and moments.