Relaxation dynamics of modulated magnetic phases in the skyrmion host GaV4S8 : An ac magnetic susceptibility study

We report on the slow magnetization dynamics observed upon the magnetic phase transitions of ${\mathrm{GaV}}₄{\mathrm{S}}₈$, a multiferroic compound featuring a long-ranged cycloidal magnetic order and a N\'eel-type skyrmion lattice in a relatively broad temperature range below its Curie temperature. The fundamental difference between ${\mathrm{GaV}}₄{\mathrm{S}}₈$ and the chiral helimagnets, the prototypical skyrmion host compounds, lies within the polar symmetry of ${\mathrm{GaV}}₄{\mathrm{S}}₈$, promoting a cycloidal instead of a helical magnetic order and rendering the magnetic phase diagram essentially different from that in the cubic helimagnets. Our ac magnetic susceptibility study reveals slow relaxation dynamics at the field-driven phase transitions between the cycloidal, skyrmion lattice and field-polarized states. At each phase boundary, the characteristic relaxation times were found to exhibit a strong temperature dependence, starting from the minute range at low temperatures, decreasing to the micro- to millisecond range at higher temperatures.