EPR AND OPTICAL-ABSORPTION STUDIES OF A VO2+-DOPED CO(NH4)2(SO4)2.6H2O SINGLE-CRYSTAL

X-band (approximately 9.5 GHz) EPR (117-413 K) and optical absorption (295 K) measurements have been carried out on a single crystal of VO2+-doped Tutton salt Co(NH4)2(SO4)2.6H2O. The impurity model of a [VO(H2O)5]2+ complex has been found to explain the EPR data well. The bonding coefficients of the [VO(H2O)5]2+ complex have been estimated using both the EPR and optical absorption data recorded presently. The spin-lattice relaxation times (tau) of the host ions, Co2+, have been estimated at various temperatures from the EPR line widths of the impurity ion, VO2+. The temperature dependence of tau has been exploited to deduce the predominance of the direct process of relaxation. The present and previously-reported EPR studies on VO2+ -doped single crystals of the isostructural M(NH4)2(SO4)2.6H2O (M = Co, Zn, Cd, Mg, Fe) have been analyzed in order to unravel the systematic of the properties of the VO2+ ion in these Tutton salts.