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.