Olena Gomonay
Antiferromagnets show ultrafast magnetic dynamics that can be effectively induced by optical or current pulses. Among plethora of materials the insulating antiferromagnets are of special interest due to low magnetic damping and reduced energy losses. However, optically generated spin torques induce precession of the Néel vector rather than switching into desirable final state. Here we discuss different scenario of ultrafast switching in noncollinear [1] and collinear [2] antiferromagnets focusing on tailoring of the pulse shapes and combination of different torques. We show that in antiferromagnets the femtosecond optical pulses generate simultaneously two types of spin torques: one scaling with spin current and one scaling with time derivative. Competition between these two opens a way to combine fast rotation of the Néel vector with the effective dynamical damping that enables effective switching into the desired final state. We further discuss the role of magnetoelastic interactions in switching which are relevant for antiferromagnets with strong magnetoelastic coupling like NiO and CoO [3]. We show that optical pulses can induce oscillations of the domain walls pinned by spontaneous strains. Strong enough pulses depin the domain walls and thus induce switching via domain wall motion. Moreover, magnetoelastic domain walls work as convertors between the different magnon modes. This opens a way of a coherent switching using the magnon modes that are most suitable for optical excitations. To conclude, we consider different ultrafast switching mechanisms that could be realised in NiO and Mn3Si antiferromagnets.
[1] O. V. Gomonay and V. M. Loktev. Low Temperature Physics, 41, 698 (2015)[2] Th. Chirac, J.-Y. Chauleau, P. Thibaudeau, O. Gomonay, and M. Viret. Phys. Rev. B 102, 134415 (2020)
[3] O. Gomonay and D. Bossini. J. Phys. D, 54, 374004 (2021)