Physical properties of the candidate quantum spin-ice system Pr₂Hf₂O₇

Physical properties of a pyrohafnate compound Pr₂Hf₂O₇ have been investigated by ac magnetic susceptibility χ_ac(T ), dc magnetic susceptibility χ(T ), isothermal magnetization M(H), and heat-capacity C_p(T )measurements on polycrystalline as well as single-crystal samples combined with high-resolution synchrotron x-ray diffraction (XRD) for structural characterization and inelastic neutron scattering (INS) to determine the crystal-field energy-level scheme and wave functions. Synchrotron XRD data confirm the ordered cubic pyrochlore (Fd¯3m) structure without any noticeable site mixing or oxygen deficiency. No clear evidence of long-range magnetic ordering is observed down to 90 mK, however the χ_ac(T ) evinces slow spin dynamics revealed by a frequency dependent broad peak associated with spin freezing. The INS data reveal the expected five well-defined magnetic excitations due to crystal-field splitting of the J = 4 ground-state multiplet of the Pr³⁺. The crystal-field parameters and ground-state wave function of Pr³⁺ have been determined. The Ising anisotropic nature of the magnetic ground state is inferred from the INS as well as χ(T) and M(H) data. Together these properties make Pr₂Hf₂O₇ a candidate compound for quantum spin-ice behavior.