Nuclear-Magnetic-Resonance Studies ofEr167in Erbium Iron Garnet

Abstract

The nuclear magnetic resonance of ${\mathrm{Er}}^{167}$ in erbium iron garnet (ErIG) has been studied at 4.2 \ifmmode^\circ\else\textdegree\fi{}K using both single crystals and polycrystalline powders. The zero-field spectrum obtained with the powder samples shows the existence of two types of rare-earth sites that would be expected when the magnetization is along a 〈100〉 direction. The two types of sites are found to have hyperfine fields of about 5.74 \ifmmode\times\else\texttimes\fi{} ${10}^{6}$ and 2.87 \ifmmode\times\else\texttimes\fi{} ${10}^{6}$ G, while the absolute magnitudes of the quadrupole coupling constants, $P=\frac{\mathrm{eQ}{V}_{\mathrm{eff}}}{4I(2I\ensuremath{-}1)h}$, for the two sites are found to be 17 and 1 MHz, respectively. With an external field of a few kilogauss applied along a 〈100〉 direction of the single crystal, the ${\mathrm{Er}}^{167}$ spectrum is found to be similar to the zero-field powder spectrum, in agreement with the fact that 〈100〉 is an easy direction of magnetization in ErIG. With the external field oriented along a 〈111〉 direction of the crystal, the observed spectrum is found to be quite different from the 〈100〉 spectrum and more difficult to interpret in detail. Hyperfine fields quadrupole coupling constants are discussed and compared with those expected from other studies. Nuclear relaxation times at the various sites have been measured and interpreted in terms of a relaxation mechanism involving the slow relaxation of the rare-earth ion.