Thermal Expansion in Substitution Alloys Based on Heavy Rare-Earth Metals $${\mathbf{R}}_{{{\mathbf{1}} - {\mathbf{x}}}}^{{\mathbf{I}}}{\mathbf{R}}_{{\mathbf{x}}}^{{{\mathbf{II}}}}{\mathbf{F}}{{{\mathbf{e}}}_{{\mathbf{2}}}}$$

A study is performed of the behavior of thermal expansion and magnetostriction in magnetically ordered substitution alloys based on heavy rare-earth metals: TbFe2, Tb0.8Zr0.2Fe2, Tb0.8Sm0.2Fe2, and Gd0.8Sm0.2Fe2. It is found that anomalies of thermal expansion observed in the alloys are mainly due to competition between exchange interactions. Invar-type features are observed in TbFe2 and Tb0.8Zr0.2Fe2 alloys in a wide range of temperatures.