Structural and magnetic studies of the low-doped chromium fluoride Cs2NaAlF6

In this paper we explore the magnetocaloric effect (MCE) of chromium-doped elpasolite Cs$_2$NaAl$_{1-x}$Cr$_x$F$_6$ (x = 0.01 and 0.62) single crystals. Our magnetization and heat capacity data show the magnetocaloric potentials to be comparable to those of garnets, perovskites and other fluorides, producing magnetic entropy changes of 0.5 J/kg$\cdot$K (x = 0.01) and 11 J/kg$\cdot$K (x = 0.62), and corresponding adiabatic temperature changes of 4 K and 8 K, respectively. These values are for a magnetic field change of 5 T at a temperature around 3 K. A clear Schottky anomaly below 10 K, which becomes more apparent when an external magnetic field is applied, was observed and related to the splitting of the Cr$^{3+}$ energy levels. These results hint at a new family of materials with potential wide use in cryorefrigeration.