Optically induced ultrafast switching dynamics in antiferromagnets*

The dynamics of magnetic materials on ultrafast timescales is a complex area of research, as it deals with nonlinear processes far from equilibrium. The potential for applications however, in particular in the development of fast and effecient magnetic storage devices, is promising. While first investigations into ultrafast demagnetisation [1] and all-optical switching [2] have focused on ferro- and ferrimagnets, more recent research in spintronics has put forward antiferromagnets as advantageous alternatives. Their vanishing net magnetisation makes them less susceptible to perturbations by external magnetic fields and their intrinsic dynamics are exchange-enhanced leading to eigenfrequencies in the terahertz range. Here, we investigate systematically how the demagnetisation and switching dynamics differ depending on the type of magnetic order. Using spin dynamics simulations in combination with density functional theory, we show how ultrafast laser-induced switching can be realised in antiferromagnets [3]. In contrast to ferro- and ferrimagnets, where a heat-induced quenching of the magnetic order is necessary to facilitate switching, we find that in antiferromagnets, the inverse Faraday effect can induce a coherent rotation of the Néel vector. We also demonstrate how a series of laser pulses can be used to reliably switch between two perpendicular magnetic states.

[1] E. Beaurepaire et al., Phys. Rev. Lett. 76, 4250 (1996).

[2] C. D. Stanciu et al, Phys. Rev. Lett. 99, 047601 (2007).

[3] T. Dannegger et al., Phys. Rev. B 104, L060413 (2021).