Magnetic Hyperfine Interactions in Dysprosium Aluminum Garnet

Abstract

The M\"ossbauer effect has been employed to investigate the magnetic hyperfine interactions of ${\mathrm{Dy}}^{161}$ in dysprosium aluminum garnet (DyAlG), which is paramagnetic (antiferromagnetic) above (below) 2.49\ifmmode^\circ\else\textdegree\fi{}K. At 4.2\ifmmode^\circ\else\textdegree\fi{}K a well-resolved paramagnetic hyperfine pattern was found that is consistent with the following interactions for the ground state of ${\mathrm{Dy}}^{161}$: ${g}_{0}{\ensuremath{\beta}}_{N}{H}_{\mathrm{eff}}=\ensuremath{-}769\ifmmode\pm\else\textpm\fi{}15$ Mc/sec and ${e}^{2}qQ=1480\ifmmode\pm\else\textpm\fi{}60$ Mc/sec. The magnetic interaction is in good agreement with the hyperfine interaction expected from the ground Kramers doublet of ${\mathrm{Dy}}^{3+}$. The excellent resolution of the 4.2\ifmmode^\circ\else\textdegree\fi{}K data allowed a more precise determination of the ratio of excited-state and ground-state moments to be obtained than has previously been reported; the ratios found were $\frac{{\ensuremath{\mu}}_{1}}{{\ensuremath{\mu}}_{0}}=\ensuremath{-}1.21\ifmmode\pm\else\textpm\fi{}0.02$ and $\frac{{Q}_{1}}{{Q}_{0}}=0.98\ifmmode\pm\else\textpm\fi{}0.03$. At 20\ifmmode^\circ\else\textdegree\fi{}K and above, the linewidths of the hyperfine lines increased owing to paramagnetic relaxation, and the data are compared with theoretical spectra whose shape is dependent on the electronic relaxation rate. The relaxation rates obtained in this manner are in approximate agreement with values extrapolated from reported electron-spin-resonance (ESR) measurements employing ${\mathrm{Dy}}^{3+}$ in the similar lattice YAIG. Although DyAlG undergoes an antiferromagnetic transition at 2.49\ifmmode^\circ\else\textdegree\fi{}K, data obtained with the sample at 1.9\ifmmode^\circ\else\textdegree\fi{}K yielded the same results as the 4\ifmmode^\circ\else\textdegree\fi{}K measurements. It is shown that the latter result is to be expected on the basis of available susceptibility and optical data.