Speaker
Description
All-optical control of magnetism is key to realizing next-generation opto-spintronic devices that integrate the speed of photonics with the memory functionality of magnetism. In particular, optical control of antiferromagnets is attractive due to their inherently fast spin dynamics and robustness against external perturbations. However, their optical detection and control remain elusive, because conventional opto-magnetic recording and magneto-optical readout techniques rely on net magnetization, which is absent in antiferromagnetic materials.
A potential strategy to overcome this fundamental limitation is to exploit magnetic multipoles other than dipole. In certain multiferroic antiferromagnets, a magnetic toroidal moment, which emerges from vortex-like spin arrangements, serves as a ferroic order parameter. The ferrotoroidic moment can couple to the linear momentum of light, giving rise to the optical magnetoelectric effect (OME), where optical properties depend on the light propagation direction. This mechanism suggests an intriguing possibility of its inverse process, namely IOME effect, in which light propagation direction controls the ferrotoroidic moment.
Here, we experimentally demonstrate the all-optical switching of antiferromagnetic domains in the ferrotoroidic LiNiPO₄ by using the IOME effect. This material crystallizes in the centrosymmetric olivine structure and exhibits an antiferromagnetic order below 20.8 K with a ferrotoroidic moment along the b axis. By irradiating intense femtosecond light pulses at 1700 nm which are resonant with the d-d transition of Ni2+ ions, we succeeded in the optical induction of the ferrotoroidic moment and its sign reversal, when light propagation is reversed. We found that this switching process is deterministic, nonvolatile, and efficient enough to switch between single-domain ferrotoroidic states with the opposite ferrotoroidic moment, i.e. between the two time-reversed antiferromagnetic domains.