Mossbauer investigation of the metal-nonmetal transition in hexagonal NiS doped with 2-at%57Fe

The Mossbauer spectra of two compositions of hexagonal Ni 1-x S doped with 2% 57 Fe are obtained at various temperatures from 4.2 to 300 K at T c =244 K in the first and 221 K in the second, a first-order phase transition occurs between an antiferromagnetic nonmetal and a paramagnetic metal; the magnetic susceptibilities, thermoelectric powers and conductivities change sharply in magnitude with a transition width of 4-5 K. The magnetic hyperfine splittings are fitted by a least squares procedure to a Brillouin function with J=2. The values of the spin disordering temperature T B at which the function cuts the zero-magnetization axis are discussed.