cube with off-center position. The off-center shift was determined from Fourier transform (FT)-ESE spectrum.
-band EPR spectrum of in single crystal along the axis, recorded at . and lines are hyperfine lines of individual ions at parallel and perpendicular orientations, respectively. The lines marked as and are due to dimers at parallel and perpendicular orientations for two spin transitions: and . The asterisks mark lines excited in pulse ESE experiments.
-band EPR spectra of in recorded along the axis at (a) 4.2 and (b) .
Possible molecular configurations of dimers in crystal. Because of an inevitable cube deformation the off-center shift can differ slightly from (see Fig. 1).
Temperature dependence of the zero-field splitting of species measured at band along the axis.
Temperature dependence of the spin-lattice relaxation rate for in (full circles) and in (Ref. 13) (open circles). The solid lines are best fits to Eq. (8) with parameters collected in Table II. The inset shows the recovery of the magnetization at to the equilibrium described by two exponential components and .
Comparison of the temperature dependence of the spin-lattice relaxation rates in fluorites doped with divalent paramagnetic ions.
Electron spin echo amplitude decay after two-pulse excitation at : (a) plot in linear scale; (b) plot in semilog scale showing that the decay is not simply ; (c) plot in semilog scale against showing linear decay. The dotted line is the best fit to the equation with and .
Temperature dependence of the dephasing time (phase memory time). The dashed line through the point at low temperatures, where spin diffusion dominates, is guide for the eyes only, whereas the solid line describes the spin-lattice process contribution to the ESE decay with temperature independent contribution from instantaneous diffusion (IDiff).
Temperature dependence of the coefficients describing ESE decay: .
Comparison of the temperature dependence of the spin-lattice relaxation rate and ESE dephasing rate for ions in and crystals.
The Fourier transform of the two-pulse ESE modulation function (FT-ESE spectrum, ESEEM spectrum) at with peaks at fluorine Larmor frequency . The inset shows the modulated ESE amplitude decay.
Temperature dependence of spin-lattice relaxation rate and phase relaxation rate for dimers in (full circles) compared with results for individual ions (open circles). The solid lines are theoretical plots according to Eq. (8) with parameters listen in Table II.
EPR parameters of spectra in and at (splitting in ).
Electron spin relaxation parameters for single ions and dimers in and crystals.
Parameters of the spin-lattice relaxation rate for divalent ions in fluorites. The line number refers to solid lines in Fig. 7.
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