Enzo Rongione
Antiferromagnets have a strong potential for future spintronic devices due to their insensitivity to perturbative external magnetic fields, absence of stray fields, and for accessing to frequencies from GHz to the terahertz (THz) regime [1–3]. However, their functionalization in thin films remains a challenging task, and requires to access and manipulate their THz resonance modes. In this work [4], we achieve a coherent emission of THz magnons triggered by fs pulses in thin films of NiO capped with platinum and detect it using THz time-domain spectroscopy (Fig. 1a). The generated THz signal has two main components as shown in Fig. 1b: i) a broadband contribution (up to 3 THz) alongside ii) a narrowband contribution centred at 1.1 THz. The latter can be associated with the THz radiation of high-frequency AFM mode of NiO. We then evidence that the THz magnon currents can be detected by THz inverse spin Hall effect in the heavy metal layer. We also demonstrate that the THz magnon excitation arises either off-resonant optical spin-torque or from spin-phonon interactions (including ultrafast strain and spin-Seebeck) depending on the growth orientation. Using ultrafast X-ray diffraction, we then evidence the presence of an ultrafast strain wave that can effectively trigger an out-of-plane precession of the Neel vector in NiO via dynamical magneto-striction in this compound. These results highlight promising perspectives for the development of narrowband and controllable THz spintronic devices using insulating AFMs.
Fig. 1. Laser induced coherent and incoherent THz emission from NiO/Pt bilayer. (a) Schematic of the setup. (b) THz emission from a low damping NiO(001)(10nm)/Pt(2nm) bilayer showing 1 ps oscillations (experiment: blue, model: brown).
References
[1] R. Cheng et al., Phys. Rev. Lett. 116, 207603 (2016). [2] J. Li et al., Nature 578, 70–74 (2020).[3] I. Boventer et al., Phys. Rev. Lett. 126, 187201 (2021). [4] E. Rongione et al., Nat. Commun. 14, 1818 (2023).