Size dependence of discrete change in magnetization in single crystal of chiral magnet Cr_1/3NbS₂

The single crystal of a chiral magnet Cr_1/3NbS₂ exhibits discrete changes in magnetization (M) in response to changes in magnetic field (H) triggered by the formation of a chiral soliton lattice (CSL). In order to provide evidence of this phenomenon, the study of the size effect is indispensable. We investigated the effects of size on this phenomenon by the use of two single crystals, (A) and (B), whose crystal sizes along the c-axis were 110 μm and 60 μm, respectively. First, in (A), the large jumps of M observed in the process of decreasing H exhibited inconsistent features, whereas the largest and second-largest jumps in (B) exhibited reproducibility for both the value of H and the magnitude of the M jumps. This confirms that these large jumps do not originate from the Barkhausen effect, as this effect would result in M jumps appearing at random values of H. When the system size of a sample becomes smaller, the features of the Barkhausen effect are suppressed. Second, as for the successive jumps observed in the H region where the rapid change in M is entirely seen for both the samples, the number of observed M jumps for (B) is more than that for (A). Indeed, the number of the domain wall due to the 2π-soliton in the CSL increases, as the c-axis length of the single crystal increases. However, a series of M jumps must appear in a limited H region below the critical field of the order of 2 kOe. The greater the number of M jumps, the more difficult the detection of the M jump will be in the H resolution of the present setup. Thus, the effects of size on the M jumps observed in the present setup can be understood within the framework of the CSL formation.