Creating and switching magnetic order with circularly-polarized phonons
ORAL · Invited
Abstract
Strong and targeted manipulation of the crystal lattice offers a powerful approach for controlling magnetic ordering, with recent studies suggesting that circular ionic motions - circularly-polarized phonons - can create angular momentum and magnetization in otherwise non-magnetic systems [1]. Such phonons, when driven at resonance, have been predicted to generate sizeable effective magnetic fields, on the order of tens of tesla [2]. Recently, using table-top techniques to test this scenario, Luo et al. detected an effective magnetic of about 1 T in CeF3 [3].
Here, we explore how magnetization can be created or even switched by light pulses tuned to excite optical phonons. Using narrow-band infrared optical pulses delivered by the free-electron laser facility FELIX [4], with wavelength ranging between 10 and 100 μm, we drive circularly-polarized transverse optical phonon modes at resonance in paramagnetic CeF3. Two-color time-resolved pump-probe measurement allow us to trace the emergent transient magnetization. By tuning the excitation wavelength, we compare the spectral emergence of the phonon magnetic moment with the spectral population of optical phonon modes.
Going further, we also demonstrate how circularly-polarized optical phonons in polar substrates can even drive switching of magnetization in a magnetic overlayer. In our experiments, we irradiate heterostructures with circularly-polarized infrared pulses. We find that the magnetic ordering in the overlayer can only be switched when the pulse drives at resonance doubly-degenerate transverse optical phonons within the substrate, with the direction of switching being controlled by the optical helicity [5]. So far, we have identified this mechanism (dubbed the ultrafast Barnett effect) in structures grown on glass-ceramic, c-cut sapphire and zinc oxide substrates, indicating that this effect could be potentially universal.
[1] M. Basini et al, Nature 628, 534 (2024)
[2] D. M. Juraschek, T. Neuman, and P. Narang, Phys. Rev. Res. 4, 013129 (2022)
[3] J. Luo et al, Science 80, 698 (2023)
[4] G.M.H. Knippels & A.F.G. van der Meer, Nucl. Instrum. Methods Phys. Res. B 144, 39 (1998)
[5] C.S. Davies et al, Nature 628, 540 (2024)
Here, we explore how magnetization can be created or even switched by light pulses tuned to excite optical phonons. Using narrow-band infrared optical pulses delivered by the free-electron laser facility FELIX [4], with wavelength ranging between 10 and 100 μm, we drive circularly-polarized transverse optical phonon modes at resonance in paramagnetic CeF3. Two-color time-resolved pump-probe measurement allow us to trace the emergent transient magnetization. By tuning the excitation wavelength, we compare the spectral emergence of the phonon magnetic moment with the spectral population of optical phonon modes.
Going further, we also demonstrate how circularly-polarized optical phonons in polar substrates can even drive switching of magnetization in a magnetic overlayer. In our experiments, we irradiate heterostructures with circularly-polarized infrared pulses. We find that the magnetic ordering in the overlayer can only be switched when the pulse drives at resonance doubly-degenerate transverse optical phonons within the substrate, with the direction of switching being controlled by the optical helicity [5]. So far, we have identified this mechanism (dubbed the ultrafast Barnett effect) in structures grown on glass-ceramic, c-cut sapphire and zinc oxide substrates, indicating that this effect could be potentially universal.
[1] M. Basini et al, Nature 628, 534 (2024)
[2] D. M. Juraschek, T. Neuman, and P. Narang, Phys. Rev. Res. 4, 013129 (2022)
[3] J. Luo et al, Science 80, 698 (2023)
[4] G.M.H. Knippels & A.F.G. van der Meer, Nucl. Instrum. Methods Phys. Res. B 144, 39 (1998)
[5] C.S. Davies et al, Nature 628, 540 (2024)
*This work was supported by the European Research Council ERC Grant Agreement No. 101115234 (HandShake).
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Presenters
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Carl S Davies
- HFML-FELIX