Estimation ofT1for divalent cobalt ions from the temperature variation of the EPR linewidths for vanadyl in rubidium cobalt sulfate hexahydrate single crystals

EPR of V${\mathrm{O}}^{2+}$ doped in ${\mathrm{Rb}}_2$CO${\left(\mathrm{S}{\mathrm{O}}_4\right)}_2$. 6${\mathrm{H}}_2$O single crystals has been studied at various temperatures from 289 to 90 K using an $X$-band spectrometer. The observation of resolved vanadyl spectra at 289 K has been interpreted in terms of a random modulation of the interaction between the vanadyl and divalent cobalt ions by the rapid spin-lattice relaxation of cobalt ions. It is found that the host spin-lattice relaxation time $T_1\propto T^{-n}$, where $n=2.02\mathrm{}$ ($\mathrm{B}\parallel \mathrm{z}$ axis) if 103 $\mathrm{K} <T <289\mathrm{}\mathrm{K}$ indicating that the Debye temperature of the host is below 103 K.