Thermodynamic and magnetic studies of novel spin ice materials*

We report systematic low temperature measurements of the dc magnetization, ac susceptibility, and heat capacity of $Dy_{2}Sn_{2-x}Sb_{x}O_{7+x/2}$ (x=0, 0.25, and 0.5), and $Dy_{2}NbScO_{7}$. We find evidence for Ising-like single ion ground states in the $Dy_{2}Sn_{2-x}Sb_{x}O_{7+x/2}$ materials, and these materials possess nearly the same zero-point entropy as the canonical spin ices $Ho_{2}Ti_{2}O_{7}$ and $Dy_{2}Ti_{2}O_{7}$. These results strongly suggest that the $Dy_{2}Sn_{2-x}Sb_{x}O_{7+x/2}$ materials studied have spin-ice states at low temperatures despite the cation disorder on the B sites of the pyrochlore lattice We also observe a somewhat reduced zero-point entropy in $Dy_{2}NbScO_{7}$, which is possibly associated with a higher level of cation disorder