Ultrasonic Paramagnetic-Resonance Absorption by Uranium Ions in Calcium Fluoride

Abstract

Ultrasonic paramagnetic-resonance absorption by uranium ions in Ca${\mathrm{F}}_2$ has been observed at an elastic-wave frequency of 9.4 Gc/sec and sample temperature of 1.5°K. The observed absorption was due only to ${\mathrm{U}}^{4+}$ ions in sites of trigonal symmetry; no absorption due to ${\mathrm{U}}^{3+}$ ions, which were also present, could be detected. The results indicate that ${\mathrm{U}}^{4+}$ can be treated by means of a spin-lattice Hamiltonian of the same form as that used previously to successfully explain spin-lattice interactions for iron-group ions, and that the spin-lattice interaction for ${\mathrm{U}}^{4+}$ in Ca${\mathrm{F}}_2$ is comparable in magnitude to that for iron-group ions in other crystals.