Synthesis and physical properties of the Kagome bilayer spin liquid Ca$_{10}$Cr$_7$O$_{28}$

We report synthesis of polycrystalline samples of the recently discovered spin liquid material Ca$_{10}$Cr$_7$O$_{28}$ and present measurements of the magnetic susceptibility $\chi$ versus temperature $T$, magnetization $M$ versus magnetic field $H$ at various $T$, and heat capacity $C$ versus $T$ at various $H$. The magnetic measurements indicate the presence of both ferromagnetic and antiferromagnetic exchange interactions with dominant ferromagnetic interactions and with the largest magnetic energy scale $\sim 10$~K. $C(T)$ shows a broad anomaly peaked at $T\approx 2.5$~K which moves to higher temperatures in a magnetic field. The evolution of the low temperature $C(T,H)$ and the magnetic entropy is consistent with frustrated magnetism in Ca$_{10}$Cr$_7$O$_{28}$.