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

Abstract

We report on the slow magnetization dynamics observed upon the magnetic phase transitions of GaV 4 S 8 , a multiferroic compound featuring a long-ranged cycloidal magnetic order and a Néel-type skyrmion lattice in a relatively broad temperature range below its Curie temperature. The fundamental difference between GaV 4 S 8 and the chiral helimagnets, the prototypical skyrmion host compounds, lies within the polar symmetry of GaV 4 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.

Magnetic phases of skyrmion-hostingGaV4S8−ySey(y=0,2Franke1, Huddart2, Hicken3 et al. 2018Phys. Rev. B322323View full textAdd to dashboardCite

“…2(b)] indicate slow dynamics at the boundaries between C, SkL, and FP phases. The same increase in χ surrounded by peaks in the susceptibility were reported for GaV 4 S 8 single crystals by Butykai et al [43]. As a consequence, we attribute the enhancement of susceptibility coinciding with the SkL phase directly to the SkL and not to an angular average over peaks marking phase transitions.…”

Direct evidence for cycloidal modulations in the thermal-fluctuation-stabilized spin spiral and skyrmion states of GaV4S8

“…These data show that close to the cycloidal-FM transition the length of |q| varies strongly, or even fluctuates, in the rhombohedral plane. This could indicate that the transition may be continuous in theory, but hysteresis effects emerge due to slow dynamics when the rearrangements of large structures are involved [28], as also found recently in MnSi [24].…”

A.C. susceptibility as a probe of low-frequency magnetic dynamics

“…In a.c. susceptibility measurements χ is found to follow the static susceptibility, but near phase boundaries χ it becomes strongly frequency-dependent. This effect has been studied in various chiral magnets, including MnSi [97], GaV 4 S 8 [98], Fe 1−x Co x Si [99] and Cu 2 OSeO 3 [100,95], and can be used to rather efficiently map out the phase boundaries and thus determine the phase diagram. An example is given in figure 23 [95] which displays a.c. susceptibility data on contour plots using the same B-T phase diagram as figure 22.…”