Influence Of Intersublattice 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 intrasublattice 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 intrasublattic nutation coupling, while they increase with intersublattice nutation in an antiferromagnet. However, we find that the THz nutation resonance frequencies decrease with both the intra- and intersublattice nutation couplings. For ferrimagnets, conversely, we calculate two nutation modes with distinct frequencies, unlike antiferromagnets. The exchangelike precession resonance frequency of ferrimagnets decreases with intrasublattice nutation coupling and increases with intersublattice nutation coupling, as antiferromagnets, but the ferromagneticlike precession frequency of ferrimagnets is practically invariant to the intra- and intersublattice nutation couplings.