Hyperfine Structure ofFe57in Yttrium-Iron Garnet from the Mössbauer Effect

The hyperfine structure of ${\mathrm{Fe}}^{57}$ in yttrium-iron garnet [${\mathrm{Y}}_3$ ${\mathrm{Fe}}_2$ ${\left(\mathrm{F}\mathrm{e}{\mathrm{O}}_4\right)}_3$] has been obtained through the Mössbauer effect. A 0.002-in. thick slice of a single crystal of yttrium-iron garnet, cut normal to a [110] direction, was used as an absorber of recoil-free gamma rays emitted by a stainless steel source. The iron in yttrium-iron garnet is located in two nonequivalent sites, tetrahedral and octahedral, each of which has an axially symmetric electric field gradient. Data were taken with the magnetization aligned in a [111] and in a [100] direction in order to produce the simplest absorption pattern. For each direction of magnetization, the absorption lines of ${\mathrm{Fe}}^{57}$ at both sites have been resolved. The magnetic field at an ${\mathrm{Fe}}^{57}$ nucleus has been found to be 3.9×${10}^5$ oe at a tetrahedral site and 4.7×${10}^5$ oe at an octahedral site when the crystal is at room temperature (∼300°K). The quadrupole coupling was found to be 7.5×${10}^{-8\mathrm{}}$ ev in the tetrahedral site and 9.0×${10}^{-8\mathrm{}}$ ev in the octahedral site.