Investigations of the singlet ground state system: PrIrSi₃

We report our comprehensive study of physical properties of a ternary intermetallic compound PrIrSi₃ investigated by dc magnetic susceptibility χ(T), isothermal magnetization M(H), thermo-remnant magnetization M(t), ac magnetic susceptibility χ_ac (T), specific heat C_p (T), electrical resistivity ρ(T), muon spin relaxation (μSR) and inelastic neutron scattering (INS) measurements. A magnetic phase transition is marked by a sharp anomaly at T_tr= 12.2K in χ(T) measured at low applied fields which is also reflected in the C_p (T) data through a weak anomaly at 12K. An irreversibility between the zero field cooled and field cooled χ(T) data below 12.2K 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 40K due to the crystal electric field (CEF) effect. An extremely small value of magnetic entropy below 12K 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 8.5meV and 18.5meV 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 92K. Our μSR data reveal a possible magnetic ordering below 30K, 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 92K is quite surprising.