Semiempirical analysis of spin-lattice relaxation in rare earth Kramers' doublets

The spin-lattice coupling constants of Kramers' doublet measured in uniaxial stress experiments, are used to calculate the spin-lattice relaxation times in the direct process range. A comparison with experimental data shows that a true spin lattice relaxation time was obtained only when T₁ was measured as a function of magnetic field at high fields. We suggest that the effect of the phonon bottleneck is important at lower fields.