Ultra-fast time resolved imaging of multiferroic orders using second harmonic generation in epitaxial BiFeO3.

Multiferroics [1] are appealing materials because of the interesting physics of the coupling between their order parameters and the significant technological interest due to their multifunctionality. Among all of them, BiFeO3 (BFO) is a material of choice because its two ordering temperatures (ferroelectric FE and antiferromagnetic AF) are well above room temperature, in addition to showing a large magnetoelectric coupling. Moreover, the AF order is currently gathering a huge amount of research work thanks to recent breakthroughs demonstrating the efficient effect of spin currents in interacting with the AF order parameter. Current-induced AF control also opens new perspectives in Terahertz magnetization dynamics, a field very much under the limelight. Because AF textures are difficult to control, magneto-electrics could offer the possibility to address the AF order through an electric field at ps timescales. Nevertheless, one difficulty in handling multiferroics lies in the challenging assessment of their coupled FE/AF textures, with characteristic sizes often in the hundreds of nanometers range.

Optical second harmonic generation (SHG) has proven to be a powerful and elegant way to image complex multiferroic textures (in particular the AF order [2]) and to disentangle the different contributions at play. Here, after discussing the SHG imaging of AF domains distributions in BFO epitaxial thin films [3], we will address their ultrafast dynamics by assessing the time evolution of the multiferroic texture when subjected to intense femtosecond light pulses. Their efficient manipulation by the internally optically rectified sub-picosecond electric fields will be discussed, paving the way to an all-optical terahertz control of the AF order, independently of the electric polarization, but still using the magnetoelectric effect.

[1] N. Spaldin and M. Fiebig, Science, 309, 391 (2005)

[2] M. Fiebig & al., Nature, 419, 818 (2002)

[3] J.-Y. Chauleau & al., Nature Materials, 16, 803 (2017)