Phase diagram of the chiral magnet Cr_(1/3)NbS_2 in a magnetic field

摘要

We construct the phase diagram of the chiral magnet Cr_(1/3)NbS_2 in a dc magnetic field (H_(dc)) using ac magnetic susceptibility measurements. At H_(dc) = 0, the ac response at the transition from the helical magnetic (HM) state to the paramagnetic (PM) state consists of a giant third-order harmonic component (M_(3ω)) and a first-order harmonic component (M_(1ω)). By applying H_(dc) perpendicular to the c axis, the HM state is transformed to the chiral soliton lattice (CSL) state, which is a superlattice tuned by H_(dc). The above giant M_(3ω) is markedly suppressed at small H_(dc). The CSL state is found to consist of CSL-1, with dominant helical texture and a poor ferromagnetic array, and CSL-2, with a large ferromagnetic array. The transition between CSL-1 and the PM state causes a linear magnetic response, the dominant component of which is the in-phase M_(1ω). With increasing temperature, CSL-2 is transformed into the forced ferromagnetic (FFM) state, and ultimately the PM state is reached. The transition between CSL-2 and the FFM state consists of a large M_(3ω) and large out-of-phase M_(1ω) as well as in-phase M_(1ω). The transition between the FMM and PM states also yields a linear magnetic response, like the CSL-1-PM-state transition. Five typical magnetic dynamics in the transitions among the HM state, CSL-1, CSL-2, FFM state, and PM state were identified according to the equivalent dynamical motion equation of a nonlinear spring model.