Magnetic and thermal properties of the mixed valence compounds Sm ₂S₃, Sm₃S₄, and Sm ₃Se₄

The magnetization and low temperature specific heat of small (20 mg) single crystals of Sm2S3, Sm3S4 and Sm3Se4 have been measured to test the crystal field model for Sm3+ in the Th3P4 structure suggested earlier for the compounds EuSm2S4 and SrSm 2S4. In this model, the Γ8 quartet is lowest but split (by ∼2.4 K) by a small noncubic crystal field. A pronounced upturn in the specific heat below 7 K is predicted. The present measurements down to 1.5 K confirm this prediction for every compound measured, the same feature occurring at almost precisely the same temperature. In addition, a comparison of the experimental susceptibilities of Sm2S3 and Sm3S4 indicates that simple addition of the contributions of the different ionic species (Sm2+ and Sm 3+) is sufficient to explain the magnetic behavior of these mixed valent Sm compounds.