  The spin inertia measurement is a recently emerged tool to study slow spin
dynamics, which is based on the excitation of the system by a train of
circularly polarized pulses with alternating helicity. Motivated by the
experimental results reported in E. A. Zhukov et al., arXiv:1806.11100 we
develop the general theory of spin inertia of localized charge carriers. We
demonstrate that the spin inertia measurement in longitudinal magnetic field
allows one to determine the parameters of the spin dynamics of resident charge
carriers and of photoexcited trions, such as the spin relaxation times,
longitudinal g-factors, parameters of hyperfine interaction and nuclear spin
correlation times.
