Magnetic Properties and Magnetocaloric Effect οf $R_{1-x}R_{x}Mn_{2}Ge_{2}$ Compounds

The magnetic and magnetocaloric properties of $Sm_{1-x}Gd_{x}Mn_{2}Ge_{2}$ compounds with 0 ≤ x ≤ 0.10 have been studied. $SmMn_{2}Ge_{2}$ is antiferromagnetic below the Néel temperature $T_{N}$ ( ≈ 400 K). Further cooling leeds to canted ferromagnetic phase below $T_C$ = 341 K. With decreasing temperature, two metamagnetic phase transitions are observed: F2-AF1 at $T_2$ = 153 K and AF1-F1 at $T_1$ = 106 K. The maximum values of magnetic entropy change | Δ $S_m$ | are found to be 1.5 J $K^{-1} kg^{-1}$ at $T_{1}$ and 2.0 J $K^{-1} kg^{-1}$ at $T_{2}$ in $SmMn_{2}Ge_{2}$. The MCE is found to increase with Gd concentration, | Δ $S_{m}(T_{1})$ | = 3.3 J $K^{-1} kg^{-1}$, while | Δ $S_{m}(T_{2})$ | is slightly enhanced for x = 0.1. The magnetocaloric effect is found to be positive at $T_{1}$ and negative at $T_{2}$.