Reinvestigation of magnetism and electric transport in a ternary transition metal chalcogenide Rb₂Ni₃S₄

The process of preparing specimens of Rb₂Ni₃S₄ single crystals grown by the flux method was reconsidered to clarify the magnetic and electronic properties of this nickel sulfide. Specimens obtained by removing fluxes with water were confirmed to have a residual ferromagnetic moment, as previously reported by the present authors. Specimens peeled a surface of as-grown crystals off by taking advantage of the quadratic layer characteristic of this crystal were ascertained to be diamagnetic and to exhibit magnetic properties intrinsic to Rb₂Ni₃S₄. However, the temperature dependence of the specific resistivity of the latter sample is similar to that of the former. Raman scattering measurement indicated that this system undergoes no structural phase transition. Magnetic measurements in Co-doped specimens were carried out to obtain further information on the host substance. The appropriate band structure of Rb₂Ni₃S₄ was calculated in terms of the full-potential linearized augmented plane-wave method in the local density approximation to understand the electronic properties of Rb₂Ni₃S₄. Through examination of the experimental results and the obtained band structure, Rb₂Ni₃S₄ was identified as a non-magnetic semiconductor in a low spin 3d⁸ configuration of Ni²⁺.