Magnetic and thermal properties of the mixed valence compounds Sm2S3, Sm3S4, and Sm3Se4

Abstract

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 SrSm₂S₄. 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 Sm³⁺) is sufficient to explain the magnetic behavior of these mixed valent Sm compounds.