EPR investigation of synthetic, doped FeS2 and RuS2 single crystals.

Synthetic FeS2 and RuS2 single crystals were prepared by the flux method using PbCl2, bismut, and tellurium as different solvents. FeS2 and some RuS2 samples were doped with elementary vanadium, other RuS2 crystals with manganese and nickel. The EPR spectra revealed Mn2+ in the low-spin state and Ni2+. The lineshape of the Mn sextet turned out to be asymmetrical. In some RuS2 samples we detected an isotropic structureless rather narrow signal with a linewidth down to 0.05 mT and attributed it to the conductivity. Its lineshape becomes symmetrical and Lorentzian by grinding the samples to a polycrystalline powder. The EPR parameters of appropriate spin-Hamiltonians were determined. The intensities of the allowed and forbidden lines depended very differently on the microwave power due to different degrees of saturation.