Spin-Lattice Relaxation ofAl27in Thulium Aluminum Garnet

The ${\mathrm{Al}}^{27}$ spin-lattice relaxation time $T_1$ has been measured between 127 and 425 °K at 8 and 14 MHz for the aluminum $a$ and $d$ sites in thulium aluminum garnet. Both sites exhibit $T_1$ dips at 275 °K which are attributed to ${\mathrm{Al}}^{27}$-${\mathrm{Tm}}^{169}$ cross relaxation. Below 190 °K the $a$-site $T_1$ magnitudes and approximately ${\omega }^{-2\mathrm{}}$ frequency dependence are explained by magnetic field fluctuations caused by the ${\mathrm{Tm}}^{3+}$ ion making transitions between its two lowest crystal-field levels with a correlation time near 4 × ${10}^{-12\mathrm{}}$ sec.