In antiferromagnetic spintronics where manipulation of the antiferromagnetic spins is a central technological challenge1), it is important to understand the dynamic properties, especially their THz spin dynamics and the magnetic damping. While both experimental and theoretical investigations of the antiferromagnetic resonance began in 1950s2), they have been recently revisited with more advanced experimental techniques3,4) as well as with more rigorous theoretical treatments5) in the context of emerging antiferromagnetic spintronics. In the early stage of the investigations, the state-of-art spectroscopy with a rather inefficient and weak far-infrared source1) was employed to investigate various antiferromagnets, such as NiO, CoO, MnO, and Cr2O3. Although their high resonant frequencies have been experimentally confirmed, the experimental technique at the time was not sufficiently sensitive to withstand detail analyses of the spin dynamics and the magnetic damping. However, thanks to the recent development of the THz technologies, frequency-domain THz spectroscopies with much better sensitivity than before has now became accessible and affordable for investigating in more detail the spin dynamics in antiferromagnets.

The talk will be based on our recent results on (1) frequency-domain THz spectroscopies of antiferromagnetic NiO and the detail analysis of the antiferromagnetic damping6), (2) observation of the THz spin pumping effect in NiO/Pt and NiO/Pd7), and (3) control of the antiferromagnetic resonance properties by cation substations of NiO8).

1)   V. Baltz et al., Rev. Mod. Phys. 90, 015005 (2018).
2)   L .R. Maxwell et al., Rev. Mod. Phys. 25, 279 (1953).
3)   T. Kampfrath et al., Nat. Photon. 5, 31 (2011).
4)   T. Satoh et al., Phys. Rev. Lett. 105, 77402 (2010).
5)   A. Kamra et al., Phys. Rev. B 98, 184402 (2018).
6)   T. Moriyama et al., Phys. Rev. Mater. 3, 051402 (2019).
7)   T. Moriyama et al., Phys. Rev. B 101, 060402 (2020).
8)   T. Moriyama et al., Phys. Rev. Mater. 4, 074402 (2020).