Electron Spin Resonance Studies with Superconducting Magnets: The Spectrum of ${\mathrm{Dy}}^{3+}$ and ${\mathrm{Sm}}^{3+}$ in Ca${\mathrm{F}}_2$

An electron spin resonance spectrometer has been constructed using strong magnetic fields up to 46 000 G generated by a superconducting magnet. It is being used for the measurement of the magnetic properties of transition elements in ionic crystals such as (a) small $g$ factors, (b) energy level separations up to 20 ${\mathrm{cm}}^{-1\mathrm{}}$, (c) isotropic and anisotropic exchange terms in spectra of pairs of paramagnetic ions, (d) spin-lattice relaxation times at high magnetic fields. The method is illustrated in the measurements of (1) the energy level separation of ${\Gamma }_8-{\Gamma }_7$ levels of ${\mathrm{Dy}}^{3+}$ in Ca${\mathrm{F}}_2$ which is found to be ${7.3}_5$±0.2 ${\mathrm{cm}}^{-1\mathrm{}}$; (2) the $g$ factors of the tetragonal spectrum of ${\mathrm{Sm}}^{3+}$ in Ca${\mathrm{F}}_2$ which are found as $g_{\mathrm{II}}=0.907\mathrm{}\pm 0.01$, $g_{\perp }=0.544\mathrm{}\pm 0.015$.