Temperature and field independence of the fluorine and lithium NMR shift tensors in lithium rare-earth tetrafluorides

The fluorine and lithium NMR line shifts have been followed in temperature from 300 to 1.3 K and in fields up to 40 kG for LiTb${\mathrm{F}}_4$ and LiHo${\mathrm{F}}_4$. The ${\mathrm{Tb}}^{3+}$ and ${\mathrm{Ho}}^{3+}$ ionic moments cause these shifts. The Li shifts are dominated by dipole interactions, whereas the F shifts also have transferred hyperfine contributions of comparable sizes. The transferred hyperfine interactions turn out to be almost isotropic and exhibiting no temperature or field dependence. In LiHo${\mathrm{F}}_4$ the line shifts are detectable within the entire temperature range. In LiTb${\mathrm{F}}_4$ the fluorine and lithium lines broaden to such an extent that they disappear in a region from 10 to 60 K and from 15 to 40 K, respectively, probably due to a long relaxation time of the Tb ionic moment.