Speaker: Unai Atxitia (Institute of Materials Science, Madrid, vendéglátó: Rózsa Levente)
Title: On the conditions for femtosecond laser-induced ultrafast toggle switching in 2D ferrimagnetic alloys
Date: Tuesday, 17 september 2024, 10:00
Place: KFKI Campus, Bldg 1, Conference room
Abstract:
The Mermin-Wagner theorem establishes that long-range magnetic order is prohibited in two-dimensional (2D) isotropic magnets with short-range interactions due to the effects of thermal fluctuations. Nevertheless, magnetically stable 2D van der Waals (vdW) materials have recently been discovered, where magnetic anisotropy plays a crucial role in stabilizing magnetic order [1]. These materials offer the opportunity to explore fundamental questions that remain unanswered [2]. A prominent example is field-free, all-optical ultrafast magnetization switching, which has been experimentally demonstrated in 3D ferrimagnetic GdFe alloys. Despite recent efforts to understand the mechanisms underlying this effect in bulk 3D ferrimagnetic alloys [3], the implications of dimensional effects in 2D systems remain undetermined.
In this study, we explore the impact of reduced dimensionality on the ultrafast magnetization switching effect in 2D ferrimagnets using atomistic spin dynamics (ASD) simulations. ASD techniques account for thermal fluctuations, which significantly influence the magnetic behavior of 2D materials [4]. Through this approach, we aim to understand how magnetic anisotropy affects the switching phenomenon in 2D structures compared to bulk systems.
Firstly, our results show that while the critical temperature in 3D systems linearly depends on the anisotropy value, this dependence is logarithmic in 2D structures. Secondly, we find that the temperature dependence of the magnetic order relaxation time, following a sudden temperature increase, shows only a slight dependence on anisotropy in 3D systems. In contrast, the behavior in 2D systems as a function of anisotropy is much more complex. Finally, we demonstrate that femtosecond laser pulse-induced toggle switching in 2D ferrimagnets is possible. However, unlike in 3D systems, where the anisotropy value has little effect on the switching process, in 2D systems, switching is only possible at relatively high anisotropy values.
Our findings pave the way for understanding the influence of dimensionality on the fundamental mechanisms of laser-induced ultrafast toggle switching. Furthermore, our results encourage the search for novel 2D ferrimagnetic materials with increased magnetic anisotropy, making them potential candidates to exhibit this effect.
[1] M. Gibertini, M. Koperski, A.F. Morpurgo, et al., Nat. Nanotechnol. 14, 408 (2019).
[2] S. Jenkins et al. Nat. Comm. 13, 6917 (2022)
[3] F. Jakobs and U. Atxitia. Phys. Rev. B 106, 134414 (2022).
[4] Q. H. Wang, A. Bedoya-Pinto, M. Blei, et al., ACS Nano 16, 6960 (2022).
