  We report our comprehensive study of physical properties of a ternary
intermetallic compound PrIrSi3 investigated by dc magnetic susceptibility
chi(T), isothermal magnetization M(H), thermo-remnant magnetization M(t), ac
magnetic susceptibility chi_ac(T), specific heat C_p(T), electrical resistivity
rho(T), muon spin relaxation (muSR) and inelastic neutron scattering (INS)
measurements. A magnetic phase transition is marked by a sharp anomaly at T_tr
= 12.2 K in chi(T) measured at low applied fields which is also reflected in
the C_p(T) data through a weak anomaly at 12 K. An irreversibility between the
zero field cooled and field cooled chi(T) data below 12.2 K and a very large
relaxation time of M(t) indicates the presence of ferromagnetic correlation.
The magnetic part of specific heat shows a broad Schottky-type anomaly near
40~K due to the crystal electric field (CEF) effect. An extremely small value
of magnetic entropy below 12 K suggests a CEF-split singlet ground state which
is confirmed from our analysis of INS data. The INS spectra show two prominent
inelastic excitations at 8.5 meV and 18.5 meV that could be well accounted by a
CEF model. The CEF splitting energy between the ground state singlet and the
first excited doublet is found to be 92 K. Our muSR data reveal a possible
magnetic ordering below 30 K which is much higher than that found from the
specific heat and magnetic susceptibility measurements. This could be due to
the presence of short range correlations well above the long range magnetic
ordering or due to the electronic changes induced by muons. The induced moment
magnetism in the singlet ground state system PrIrSi3 with such a large
splitting energy of 92 K is quite surprising.
