Motivated by the current strong constraints on the spin-independent dark matter (DM)-nucleus scattering, we investigate the spin-dependent (SD) interactions of the light Majorana DM with the nucleus mediated by an axial-vector boson. Due to the small nucleus recoil energy, the ionization signals have now been used to probe the light dark matter particles in direct detection experiments. With the existing ionization data, we derive the exclusion limits on the SD DM-nucleus scattering through Migdal effect in the MeV-GeV DM mass range. It is found that the lower limit of the DM mass can reach about several MeVs. Due to the momentum transfer correction induced by the light mediator, the bounds on the SD DM-nucleus scattering cross sections can be weakened in comparison with the heavy mediator.
SD DM-NUCLEUS SCATTERING THROUGH MIGDAL EFFECTIn theories where the DM couples predominantly to the spin of the nucleus, the corresponding interactions are dubbed as spin-dependent. In contrast with the SI couplings, there is no coherent enhancement in the spindependent DM-nucleus scattering cross section because the spins of nucleons in a nucleus tend to cancel in pairs.