Spin-Lattice Interactions ofNd3+andU3+Ions in Calcium Fluoride Measured by Electron Spin Resonance in Uniaxially Stressed Crystals

Abstract

The spin-lattice Hamiltonian for ${\mathrm{Nd}}^{3+}$ and ${\mathrm{U}}^{3+}$ ions in sites of tetragonal symmetry in calcium fluoride has been determined experimentally. The components of a spin-lattice coupling tensor were from measurements of the effect of static uniaxial stress on the ESR spectra of these ions. The effect of stress on the ions, which have Kramers-doublet ground states, was interpreted in terms of an effective spin-lattice Hamiltonian of the form $H_{\mathrm{SL}}=\Sigma {\mathrm{ijmn}}^{}{G}_{\mathrm{ijmn}}{e}_{\mathrm{mn}}{H}_i{S}_j$, where $e_{\mathrm{mn}}$ is the lattice strain tensor, and $G_{\mathrm{ijmn}}$ is the spin-lattice coupling tensor. Seven independent components of the $G$ tensor were determined for each ion. The resulting spin-lattice Hamiltonian was used to calculate the strength of ultrasonic spin-resonance absorption and the direct one-phonon spin-lattice relaxation time for these ions. The calculated relaxation time is in serious disagreement with reported experimental measurements, but no verifiable explanation of this discrepancy has been found.