  We report the doping-induced antiferromagnetic state and Fermi liquid state
that are connected by a superconducting region in a series of
CeIrIn$_{5-x}$Hg$_x$, CeIrIn$_{5-x}$Sn$_x$ and CeIr$_{1-x}$Pt$_x$In$_5$ single
crystals. Measurements of the specific heat $C(T)$ and electrical resistivity
$\rho(T)$ demonstrate that hole doping via Hg/In substitution gives rise to an
antiferromagnetic ground state, but substitutions of In by Sn or Ir by Pt
(electron doping) favor a paramagnetic Fermi liquid state. A cone-like
non-Fermi liquid region is observed near CeIrIn$_5$, showing a diverging
effective mass on the slightly Hg-doped side. The obtained temperature-doping
phase diagram suggests that CeIrIn$_5$ is in proximity to an antiferromagnetic
quantum critical point, and heavy fermion superconductivity in this compound is
mediated by magnetic quantum fluctuations rather than by valence fluctuations.
