An EPR Study of the Pyrites Co(x)Fe(1-X)S2, Ni(x)Fe(1-x)S2, and Co(x)Ni(y) Fe(1-x-y)S2.

The paper reports on an EPR study of the pyrite solid solutions CoxFe1-xS2, and CoxNiyFe1-x-yS2. The single-ion spectrum for dilute Ni2 in a pyrite structure was fitted to a spin Hamiltonian. The single-ion spectrum for Co2 in FeS2 showed evidence of dynamic Jahn-Teller activity, with a broad, isotropic line. At metallic concentrations, FeS2Co displayed the classically asymmetric, isotropic line of a conduction electron but with an unusually high g-value indicating the partial ionic character of narrow band electrons. The system FeS2NiCo displayed both the broad lines characteristic of the itinerant Cobalt eg electrons and the localized Ni2 spectrum. The peculiar Ni2 lineshapes resulting from exchange effects with the itinerant electrons are analyzed on the basis of existing s-d interaction theory. Author Modified Abstract