Magnetic properties of some cubic rare-earth elpasolite hexafluorides

Single crystals of cubic $A_{2}BR{F}_6$ ($A,B=\mathrm{alkali} \mathrm{metals}, R=\mathrm{rare} \mathrm{earth}$) have been studied magnetically. If $R$ is a Kramers ion, the system orders well below 1 °K. For non-Kramers ions, we find in general Van Vleck behavior at low temperature. Crystal-field splittings are found to be in poor agreement with point-charge model calculations. Besides crystal-field aspects, a number of hyperfine properties will also be discussed.