Anomalous spiked structures in ESR signals from the chiral helimagnet CrNb3S6

Abstract

We have performed X-band electron spin resonance (ESR) measurements on a single crystal of the metallic chiral helimagnet ${\mathrm{CrNb}}_{3}{\mathrm{S}}_{6}$ from 3.5 to 180 K and for the external magnetic fields ${H}_{\mathrm{ext}}$, up to 4 kOe, perpendicular to the $c$ axis (the helical axis of ${\mathrm{CrNb}}_{3}{\mathrm{S}}_{6}$). This field-crystalline configuration is expected to provide the chiral soliton lattice (CSL) state in this system. The main resonance line can be fit with a Dysonian function above ${T}_{\mathrm{c}}=127\phantom{\rule{0.0pt}{0ex}}\phantom{\rule{4pt}{0ex}}\mathrm{K}$, but additional features in the spectra were observed below 105 K. Specifically, spiked anomalies superposed on the main signals were observed for magnetic fields between ${H}_{\mathrm{c}1}$ and ${H}_{\mathrm{c}2}$ that are the appearing and disappearing fields of the spiked anomalies, respectively. The resulting magnetic field vs temperature phase diagram possesses three regions, which are interpreted as different dynamical responses in the CSL phase. In addition, the values of ${H}_{\mathrm{c}2}$ are close to those reported by the ${d}^{2}M/d{H}^{2}$ curve [Tsuruta et al., Phys. Rev. B 93, 104402 (2016)]. Furthermore, the field range between ${H}_{\mathrm{c}1}$ and ${H}_{\mathrm{c}2}$, where the spiked anomalies exist, depends on the field direction and shifts to higher fields when turning to the $c$ axis, thereby providing additional evidence that these spiked anomalies must be related to the chiral soliton dynamics.