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Influence of inter-sublattice coupling on the terahertz nutation spin dynamics in antiferromagnets

Spin nutation resonance has been well-explored in one-sublattice ferromagnets. Here, we investigate the spin nutation in two-sublattice antiferromagnets as well as, for comparison, ferrimagnets with inter-and intra-sublattice nutation coupling. In particular, we derive the susceptibility of the two-sublattice magnetic system in response to an applied external magnetic field. To this end, the antiferromagnetic and ferrimagnetic (sub-THz) precession and THz nutation resonance frequencies are calculated. Our results show that the precession resonance frequencies and effective damping decrease with intra-sublattice nutation coupling, while they increase with inter -sublattice nutation in an antiferromagnet. However, we find that the THz nutation resonance frequencies decrease with both the intra-and inter-sublattice nutation couplings. For ferrimagnets, conversely, we calculate two nutation modes with distinct frequencies, unlike antiferromagnets. The exchange-like precession resonance frequency of ferrimagnets decreases with intra-sublattice nutation coupling and increases with inter-sublattice nutation coupling, like antiferromagnets, but the ferromagnetic-like precession frequency of ferrimagnets is practically invariant to the intra and inter-sublattice nutation couplings.