Anomalous Order in $R_3\text{Ni}_{30}\text{B}_{10}$ $(R = \text{La}, \text{Ce})$

We report the synthesis of single crystals of the $R_3\text{Ni}_{30}\text{B}_{10}$ $(R = \text{La}, \text{Ce})$ system which realizes the tetragonal $P4/nmm$ (No. 129) space group. We performed single crystal, transmission X-ray diffraction measurements to determine the crystal structure. Additionally, we characterized the samples through magnetization, resistivity, and heat capacity measurements. The $R = \text{Ce}$ system exhibits mixed-valence states and we observe maxima in the heat capacity at $T_1^* = 6 \, \text{K}$ and $T_2^* = 2 \, \text{K}$ (both absent for $R = \text{La}$) with no corresponding features in the resistivity or magnetization. We discuss the potential roles of multipolar and short-ranged/partial order in connection to the $T_1^*$ anomalous order.