In antiferromagnetic materials (AF), the magnetic moments of atoms point towards opposite directions between neighbors, resulting in an absence of magnetization. Such conditions make it difficult to probe the AF order, which also exhibits very low sensitivity to an exterior magnetic field. Yet these materials have been the focus of many studies, as an AF memory would be ultra-compact, insensitive to electromagnetic interferences, and could reach a magnetization reversal frequency of the order of the terahertz (10¹² Hz).

But how can scientists control the AF order in a material? Physicists from IRAMIS were able to visualize the AF order of bismuth ferrite (BiFeO₃) using "second-harmonic generation". The presence of an AF order breaks a spatial "symmetry" in the crystal, which makes it possible to emit light at twice the frequency of the incident femtosecond (10^-15 s) infrared laser beam. Ultimately allowing the formation of the image of the magnetic domains of bismuth ferrite.

This technique has allowed scientists to monitor the development of antiferromagnetic domains under the influence of external stimuli such as an electric field or an optical excitation.

This study is the result of a collaboration with Unité mixte de physique (CNRS, Thales, Paris-Sud University, Paris-Saclay University), in Palaiseau, France.