  A quantum critical point (QCP) between the antiferromagnetic and the
paramagnetic phases was realized by applying a hydrostatic pressure of ~ 7 GPa
on single crystals of NiS_{2} pyrite with a low residual resistivity, rho_{0},
of 0.5 mu-Omega-cm. We found that the critical behavior of the resistivity,
rho, in this clean system contrasts sharply with those observed in its
disordered analogue, NiS_{2-x}Se_{x} solid-solution, demonstrating the
unexpectedly drastic effect of disorder on the quantum criticality. Over a
whole paramagnetic region investigated up to P = 9 GPa, a crossover
temperature, defined as the onset of T^{2} dependence of rho, an indication of
Fermi liquid, was suppressed to a substantially low temperature T sim 2 K and,
instead, a non Fermi liquid behavior of rho, T^{3/2}-dependence, robustly
showed up.
