Abstract :
The ever-growing demand for data consumption is driving new information technologies to process larger volumes of data at a faster rate and with lower energy costs. In this respect, mastering the underlying mechanisms of the generation and manipulation of spin currents at sub-picosecond timescales stands as an interesting playground to meet these challenges. On the other hand, antiferromagnetic textures look very attractive as they present several interesting features. Indeed, they offer appealing dynamical properties since their magnetic resonances directly lie in the THz range. Besides, it has been shown, that “magnonic-type” spin currents can be propagated in those antiferromagnetic insulators even over considerable distances in single crystals. However, even though this has been clearly evidenced in the DC and GHz regime, opened questions remain regarding spin current transport properties in antiferromagnets at picosecond timescales, i.e. when spin currents coherently match a specific antiferromagnetic THz resonance. This is the main objective of this thesis work in which we aim to study the transfer of spin angular momentum to antiferromagnetic insulators at picosecond and sub-picosecond timescales. Measuring directly the antiferromagnetic dynamics is a great challenge due to their intrinsic lack of net magnetization. To overcome this difficulty, our experimental approach consists in evaluating the effect of the antiferromagnetic reservoir (e.g. NiO, Cr₂O₃, BiFeO₃) on the ultrafast demagnetization of an adjacent ferromagnetic layer – acting here as a spin injector -, by performing time-resolved magneto-optical measurements (Tr-MOKE). We will also see how the appropriate use of model antiferromagnetic materials enables us to directly probe their intrinsic dynamics. Thus, in this thesis we will present the clear signature of spin-angular momentum transfer to the antiferromagnetic textures via the opening of an additional momentum dissipation channel providing evidence for the triggering of THz antiferromagnetic dynamics by ultrafast spin-transfer torque and paving the way for the use of these materials for ultrafast information manipulation.