Vibrations of the crystal lattice have a significant impact on the orbital dynamics of the electrons, and through it, on spins. Recently, ultrafast optical techniques have provided new insights into the coherent coupling of individual phonon and spin modes [1]. Ultrafast excitation of phonons resulting in drastic repopulation of phononic system was even shown to be able to modify the fundamental magnetic interactions [2]. And last but not least, very recently time-resolved X-ray scattering and electron diffraction experiments demonstrated the angular momentum transfer from magnetization to the phonon system, on a femtosecond time scale, dubbed ultrafast Einstein-de-Haas effect [3,4]. It should therefore be possible to realize the opposite process, by changing the lattice and thus controlling the magnetization, on the same time scale – in femtoseconds!

We have recently demonstrated how the resonant excitation of circularly-polarized optical phonons in paramagnetic substrates can permanently reverse the magnetic state of the overlayer [5]. With the handedness of the phonons steering the direction of switching, such effect offers a selective and potentially universal method for ultrafast non-local control over magnetic order. The helicity-dependence of the switching implies that the lattice vibrations excited in the substrate deliver a directional field that pushes the magnetization towards a switched or non-switched state. The nature of such field is however completely unknown at present.

Moreover, a different and ultimately universal behaviour, characterized by displacive modification of crystal potentials, is driven by linearly-polarized excitation. The magnetic switching was shown to create very peculiar quadrupolar spatial patterns [6], confirming the mechanism. The mechanism appears to be very universal, as observed in variety of systems [7]. The dynamics of the domain formation was shown to proceed via a strongly inhomogeneous magnetic state resulting in a self-organization of magnon-polarons [8] and formation of magneto-elastic solitons.

References:

1. V. V. Temnov, Nature Phot. 6, 728 (2012).
2. S. F. Maehrlein et al, Science Adv. 4, eaar5164 (2018).
3. C. Dornes et al, Nature 565, 209 (2019).
4. S. R. Tauchert et al, Nature 602, 73 (2022).
5. C. S. Davies, F. G. N. Fennema, A. Tsukamoto, I. Razdolski, A. V. Kimel & A. Kirilyuk, Nature 628, 540 (2024).
6. A. Stupakiewicz, C.S. Davies, K. Szerenos, D. Afanasiev, K.S. Rabinovich, A. V. Boris, A. Caviglia, A.V. Kimel, & A. Kirilyuk, Nature Phys. 17, 489 (2021).
7. M. Kwaaitaal, D.G. Lourens, C.S. Davies & A. Kirilyuk, Nature Phot. 18, 569 (2024).
8. M. Gidding, T. Janssen, C.S. Davies & A. Kirilyuk, Nature Commun. 14, 2208 (2023).