Analysis of anomalous negative magnetic contribution to thermal expansion in Sm0.80B6 and pseudobinary compounds Sm1−xLaxB6 (x = 0, 0.10, 0.22, 0.50)

This study is the first attempt to apply the two-level Weiss model for the invar alloy to intermediate-valence samarium systems. This model is instrumental in giving a quantitative characterisation of the anomalous magnetic contribution to the coefficient of thermal expansion (CTE) of Sm_0.80B₆ and Sm_1−xLa_xB₆ (x = 0, 0.10, 0.22, 0.50). A good agreement between the experimental and calculated magnetic contributions to the CTE is achieved for Sm_0.78La_0.22B₆ over the temperature range from 0 K to 210 K. In other systems, a good fit is obtained over shorter temperature ranges. The model parameters and the dependence of the CTE minimum on the level of lanthanum doping in SmB₆ are presented.