We report low-temperature and high-pressure measurements of the electrical resistivity $\rho \left(T\right)$ of the antiferromagnetic compound $\mathrm{Ni}{\mathrm{S}}_2$ in its high-pressure metallic state. The form of $\rho (T,p)$ suggests the presence of a quantum phase transition at a critical pressure $p_c=76\pm 5\mathrm{kbar}$. Near $p_c$, the temperature variation of $\rho \left(T\right)$ is similar to that observed in $\mathrm{Ni}{\mathrm{S}}_{2-x}{\mathrm{Se}}_x$ near the critical composition $x=1$, where metallic antiferromagnetism is suppressed at ambient pressure. In both cases, $\rho \left(T\right)$ varies approximately as $T^{1.5}$ over a wide range below $100\mathrm{K}$. This lets us assume that the high-pressure metallic phase of stoichiometric $\mathrm{Ni}{\mathrm{S}}_2$ also develops itinerant antiferromagnetism, which becomes suppressed at $p_c$. However, on closer analysis, the resistivity exponent in $\mathrm{Ni}{\mathrm{S}}_2$ exhibits an undulating variation with temperature not seen in NiSSe $(x=1)$. This difference in behavior may be due to the effects of spin-fluctuation scattering of charge carriers on cold and hot spots of the Fermi surface in the presence of quenched disorder, which is higher in NiSSe than in stoichiometric $\mathrm{Ni}{\mathrm{S}}_2$.

• Received 26 September 2006

DOI:https://doi.org/10.1103/PhysRevB.77.115135