Cluster glass behavior and magnetocaloric effect in the hexagonal polymorph of disordered Ce$_2$PdGe$_3$

In this work, we study the hexagonal variant of the $\text{Ce}_2\text{PdGe}_3$ system that crystallizes in the $\text{AlB}_2$-type structure (space group $P6/mmm$, $hP3$) and exhibits cluster spin glass type behavior. The physical properties were studied by magnetization, heat capacity and electric resistivity, which showed that $\text{AlB}_2$-type $\text{Ce}_2\text{PdGe}_3$ ($h\text{-Ce}_2\text{PdGe}_3$) can be classified as a cluster glass material with the freezing temperature $T_f = 3.44 \text{ K}$ in contrast to the behavior of the previously described tetragonal variant, which shows a double antiferromagnetic transition at $T_{N1} = 11 \text{ K}$ and $T_{N2} = 2.3 \text{ K}$. The X-ray photoelectron spectroscopy measurements reveal that the $\text{Ce } 4f$ states are well localized. In addition, we examine the magnetocaloric effect in this compound. The maximum values of magnetocaloric parameters appear in the vicinity of $7\text{--}9 \text{ K}$. For a magnetic field change of $50 \text{ kOe}$, the value of the change in magnetic entropy is $2.6(1) \text{ J kg}^{-1} \text{ K}^{-1}$ and the adiabatic temperature change is $\sim 8 \text{ K}$.