First-Order-Paramagnetic-Antiferromagnetic, Metallic-Semiconducting Transition in Nickel Sulfide

Publisher Website
Google Scholar
Abstract
The first-order transition at 263°K occurring in the nickel-arsenide form of NiS has been examined in more detail by neutron diffraction, electrical resistivity, and magnetic-susceptibility measurements on high-purity samples. Neutron powder intensity data at 4.2°K and at room temperature show that the NiAs crystal structure is retained below the transition, no lattice distortion being observed, and confirm the antiferromagnetic ordering reported previously. The intensity data also show that at most only 1% of the nickel atoms migrate from their normal octahedral sites to tetragonal interstitial sites upon being warmed from 4.2°K to room temperature, and no sudden migration is observed at the transition. This is in contrast to the nickel-arsenide form of MnBi, in which 10% of the manganese atoms are reported to migrate suddenly to the tetragonal sites upon being warmed through the first-order transition observed at 633°K. The magnetic moment per Ni2+ ion at 4.2°K as determined from the mixed nuclear and magnetic (101) reflection is 1.66±0.08 μB and at 260°K, just three degrees below the transition, the measured moment is 1.50±0.10 μB. Electrical-resistivity measurements on a compressed-powder sample show an abrupt increase by a factor of about 40 upon cooling through the transition. Above the transition, the resistivity is linear with the temperature, with a positive temperature coefficient indicative of metallic conductivity, and is calculated to be ρ(T)/ρ(0°C) = 0.76+6.8 × 104T(°K). Below the transition, a plot of logρ(T)/ρ(0°C) vs 1/T gives an activation energy for semiconduction of 0.12 eV. The powder magnetic susceptibility at room temperature is 2.24×106 emu/g. Upon cooling, the susceptibility (χ) decreases slightly down to the transition, where it abruptly increases by 16%. Below the transition, χ decreases linearly with temperature. The magnitude of χ below the transition, however, depends on the magnitude of the external applied magnetic field at the time the transition is traversed. Details of this work are to be published elsewhere.

This publication has 2 references indexed in Scilit: