Low-Temperature Magnetic Properties of Some Rare-Earth Garnet Compounds

Low-temperature magnetic susceptibility measurements have been carried out on single crystals of ${\mathrm{Dy}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}$ , ${\mathrm{Dy}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ , ${\mathrm{Er}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}$ , ${\mathrm{Er}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ , and diamagnetic ${\mathrm{Y}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}$ and ${\mathrm{Y}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ containing nominally 1% Dy and Er. The dilute samples have also been investigated by paramagnetic resonance (9 kMc at 4.2°K), and with the exception of Dy in ${\mathrm{Y}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}$ for which no resonance was found, the $g$ tensors of the ground state doublets have been determined in each case. A wide range of principal $g$ values was found (1 to 11) and considerable differences between corresponding Al and Ga compounds were observed. These results show that the electronic ground states of the ${\mathrm{Dy}}^{\text{3+}}$ and ${\mathrm{Er}}^{\text{3+}}$ ions are in general very anisotropic in these structures, and that their magnetic properties are very sensitive to small changes of environment. The susceptibility measurements also indicated the presence of low-lying crystal field states, and a weak, but rather complex, interaction between the rare-earth ions. In the case of ${\mathrm{Dy}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}$ the interactions lead to antiferromagnetic ordering at 2.5°K. Difficulties in applying these results to the interpretation of the properties of ferrimagnetic garnets containing Dy and Er are discussed.