AC magnetic susceptibility in the antiferromagnetic transition of α-Dy2S3 and the weak-ferromagnetic transition of α-Sm2S3

Rare earth sesquisulfides alpha-R2S3 (R = Dy, Sm) possess an orthorhombic crystal structure having two crystallographically inequivalent rare-earth sites, R1 and R2. The compound alpha-Dy2S3 exhibits successive antiferromagnetic transitions at TN1 = 11.4 K and TN2 = 6.4 K, while alpha-Sm2S3 shows successive weak-ferromagnetic transitions at TC1 = 3.6 K and TC2 = 1.8 K. Furthermore, they are fascinating because they exhibit a very large increase and recovery in electrical resistivity within a narrow temperature range just above TN2 and TC1, respectively. In this study, the AC magnetic susceptibility was measured near TN1 and TN2 using alpha-Dy2S3 single crystals, and near TC1 using alpha-Sm2S3 single crystals. The imaginary part of AC susceptibility for each compound exhibited sharp peak near TN2 or TC1, respectively, clearly indicating a phase delay in the magnetic moment motion within each temperature range, where it could not follow the changes in the AC magnetic field. Furthermore, it was found that in alpha-Dy2S3, the peak height increases with increasing AC magnetic field frequency, whereas in alpha-Sm2S3, it decreases, reflecting the difference in magnetic ordering between the two compounds.