Drastic change of the electrical resistivity related to the novel magnetic phase transition in α-Sm2S3

Magnetization and electrical resistivity of α-Sm2S3 have been investigated by using single crystals. The temperature dependence of the magnetization; M(T), demonstrates a magnetic transition at around T = 4.5 K. The M(T) shows abrupt rise below 5K with decreasing temperature in the low magnetic filed of H = 100 Oe. Zero-field-cooled M(T) shows a sudden decrease with marking a maximum at 4.5 K, while field-cooled M(T) keeps steady rising around this temperature. The magnetization M(H) in the magnetic field along the c-axis shows a ferromagnetic hysteresis at the lower temperature than TC = 4.5 K, although its magnitude is much smaller than the value for the full Sm3+ moment. The resistivity ρ(T) indicates a double peak having the maxima at T = 4.65 and 3.3 K in no magnetic field. The ratio of ρ(4.65 K) to ρ(6.0 K) is extremely large as it exceeds 100. The double peak diminishes rapidly with increasing magnetic field. The negative giant magneto-resistance effect having the magneto-resistance ratio of −99 % at H = 10 kOe has been observed at T = 4.5 K

Specific-heat study on successive magnetic transitions in α-Dy2S3 single crystals under magnetic fields

Specific heat measurements in magnetic fields have been performed on !-Dy2S3 single crystal that shows successive magnetic transitions at TN1 = 11.4 K and TN2 = 6.4 K. The specific heat in no magnetic field exhibits sharp peaks at both temperatures of TN1 and TN2.The change of magnetic entropy across each transition is estimated as Rln2/2 per mol-Dy,which suggests magnetic moments on only one Dy site between two crystallographically inequivalent Dy sites order at each transition temperature. When the magnetic field is applied along the b-axis of the orthorhombic system, two peaks of the specific heat shift toward lower temperatures. On the other hand, the magnetic field perpendicular to the b-axis shifts the peaks toward higher temperatures. The TN1 shifts to 9.6 K (H// b) and 12.5 K (H⊥b) under the magnetic field of 2 T. The peak of TN2 broadens gradually with increasing magnetic field for each direction, and the peak is consequently obscure under the field of 2 T