Low-temperature heat capacity of antiferromagnetic ternary rare-earth iron silicidesM2Fe3Si5

The low-temperature heat capacity of antiferromagnetic ternary iron silicides $M_2{\mathrm{Fe}}_3{\mathrm{Si}}_5$ ($M=\mathrm{Sm}, \mathrm{Gd}-\mathrm{Yb}$) 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.