Signatures of spin-glass behavior in the induced magnetic moment system PrRuSi₃

We have investigated the magnetic and transport properties of a ternary intermetallic compound PrRuSi₃ using dc magnetization, ac susceptibility, specific heat, electrical resistivity, neutron diffraction, inelastic neutron scattering, and μSR measurements. The magnetic susceptibility and specific heat data reveal the signatures of spin-glass behavior in PrRuSi₃ with a freezing temperature of 9.8 K. At low magnetic fields, we observe two sharp anomalies (at 4.9 and 8.6 K) in magnetic susceptibility data. In contrast, the specific heat data show only a broad Schottky-type anomaly centered around 10 K. However, μSR reveals very low frequency coherent oscillations at 1.8 K with an onset of fast relaxation below 12 K indicating a long-range magnetically ordered ground state with very small moment. On the other hand, no magnetic Bragg peaks are observed in low-temperature neutron diffraction data at 1.8 K. These two contradictory ground states, spin glass versus magnetic order, can be explained if the spin-glass behavior in PrRuSi₃ is considered due to the dynamic fluctuations of the crystal field levels as has been proposed for spin-glass behavior in PrAu₂Si₂. Two sharp inelastic excitations near 2.4 meV and 14.7 meV are observed in the inelastic neutron scattering (INS) spectra between 4 K and 50 K. Further, exchange coupling J_ex obtained from the analysis of INS data with the CEF model provides evidence for the spontaneously induced magnetic order with a CEF-split singlet (Γ_t4) ground state. However, the exchange coupling seems to be close to the critical value for the induced moment magnetism; therefore we tend to believe that the dynamic fluctuations between the ground-state singlet and excited doublet CEF levels is responsible for spin-glass behavior in PrRuSi ₃.