Low-temperature heat capacity of antiferromagnetic ternary rare-earth iron silicides M 2 Fe 3 Si 5

The low-temperature heat capacity of antiferromagnetic ternary iron silicides ${M}_{2}{\mathrm{Fe}}_{3}{\mathrm{Si}}_{5}$ ($M=\mathrm{Sm}, \mathrm{Gd}\ensuremath{-}\mathrm{Yb}$) has been measured from 0.5 to 30 K. Antiferromagnetic ordering temperatures range from 1.06 to 10 K for these materials including multiple magnetic transitions in ${\mathrm{Sm}}_{2}$${\mathrm{Fe}}_{3}$${\mathrm{Si}}_{5}$, ${\mathrm{Tb}}_{2}$${\mathrm{Fe}}_{3}$${\mathrm{Si}}_{5}$, and ${\mathrm{Er}}_{2}$${\mathrm{Fe}}_{3}$${\mathrm{Si}}_{5}$. Magnetic ordering via the Ruderman-Kittel-Kasuya-Yosida interaction is indicated, even in the presence of large crystalline electric field effects. Entropy considerations indicate the magnetic ground state is a doublet in all of these materials except ${\mathrm{Gd}}_{2}$${\mathrm{Fe}}_{3}$${\mathrm{Si}}_{5}$. Anomalous behavior is observed with respect to spin-wave and nuclear contributions to the total heat capacity, crystalline electric field effects, and critical behavior.