Single crystal EPR and optical studies of paramagnetic ions doped zinc potassium phosphate hexahydrate--part I: Cu(II)--a case of orthorhombic symmetry

Identification of static JT in copper(II) doped hexaimidazole M(II) lattices: M=Co and Ni: an EPR study

Single crystal EPR studies on Cu(II) doped paramagnetic host lattices, hexaimidazole M(II) dichloride tetrahydrate (M=Co and Ni), isomorphous with M=Zn, have been carried out from room temperature to 77K to understand the nature of Jahn-Teller (JT) distortion in these paramagnetic host systems. The paramagnetic impurity, doped in the present two paramagnetic host lattices, shows anisotropic EPR spectra with superhyperfine from ligands, even at room temperature. An interesting observation noticed in the EPR spectra at room temperature is that there are more resonances corresponding to the second site in the paramagnetic hosts than in the diamagnetic host at 4.2K. This difference in behavior between the diamagnetic and paramagnetic host lattices indicates a change in the depth of the JT valleys. The spin Hamiltonian parameters are evaluated for Cu(II) ion in both the host lattices and the relaxation times have been calculated for the ion in cobalt host lattice only.

Single crystal EPR studies of paramagnetic ions doped zinc potassium phosphate hexahydrate; Part III: Mn(II)-a case of rhombic distortion

Single crystal electron paramagnetic resonance (EPR) studies of Mn(II) doped zinc potassium phosphate hexahydrate have been carried out at room temperature. Single crystal rotations along the three orthogonal axes indicate orthorhombic symmetry with spin-Hamiltonian parameters as: g(xx) = 1.9997; g(yy) = 1.9538; g(zz) = 1.9524, D(xx) = 15.49 mT; D(yy) = 0.22 mT; D(zz) = -15.71 mT, A(xx) = 11.70 mT; A(yy) = 10.53 mT; A(zz) = 10.42 mT and a = 0.8 x 10(-4) cm(-1). A large E term indicates considerable distortion from axial symmetry. The impurity is found to enter the lattice substitutionally. The distortion axis for the impurity has been identified along one of the Zn-O bond directions in the crystal.

Single crystal EPR study of Cu(2+) in cobalt ammonium phosphate hexahydrate: a case of low hyperfine coupling constant and measurement of spin-lattice relaxation times

Single crystal electron paramagnetic resonance (EPR) studies of Cu(II) doped cobalt ammonium phosphate hexahydrate have been carried out from 300 to 77 K, with single crystal rotation in all the three planes at 153 K, since the spectra are well resolved at this temperature. The angular variation studies indicate only one site in substitutional position with spin-Hamiltonian parameters as g: 2.404, 2.155, 2.063 and A: 11.58, 3.49, 2.07 mT. The reduction in one of the principal A value has been explained by considering considerable admixture of d(x(2)-y(2)) ground state with d(zeta(2)) excited state. The admixture coefficients of ground state wave function are: a = 0.2500; b = 0.9663; c = 0.0520; d = 0.0210; e = -0.0210, where a and b correspond to admixture coefficients for d(zeta(2)) and d(x(2)-y(2)) , respectively. Parameters kappa = 0.5140; P = 113 X 10(-4) cm(-1); alpha(2) = 0.7897; alpha = 0.8887; and alpha' = 0.5262 have also been calculated, indicating considerable covalency. The powder spectrum at room temperature is unresolved, whereas it is better resolved at 77 K, with spin-Hamiltonian parameters matching well with the single crystal values of 153 K. Powder spectrum at 77 K has been simulated, which agrees with the experimental one. The spin-lattice relation times are measured from the line width of the resonance lines recorded at different temperature.

Single crystal EPR and optical studies of paramagnetic ions doped zinc potassium phosphate hexahydrate--part II: VO(II)--a case of substitutional site

Single crystal electron paramagnetic resonance (EPR) studies were carried at room temperature for VO(II) doped zinc potassium phosphate hexahydrate. The results indicate that the paramagnetic impurity has entered the lattice only substitutionally, as confirmed by the single crystal rotations. The spin Hamiltonian parameters calculated from the spectra are g parallel = 1.9356, g perpendicular = 1.9764, A parallel = 200.9 G and A perpendicular = 76.5 G. The optical absorption spectrum exhibits three bands (800, 670 and 340 nm) suggesting the C4v symmetry and the optical parameters evaluated are Dq = 1492, Ds = -3854 and Dt = 186 cm(-1).