Physical properties of the candidate quantum spin-ice systemPr2Hf2O7

Abstract

Physical properties of a pyrohafnate compound Pr2Hf2O7 have been investigated by ac magnetic susceptibility χac(T ), dc magnetic susceptibility χ(T ), isothermal magnetization M (H) and heat capacity Cp(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 (F d3m) 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 χac(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 Pr 3+ . The crystal field parameters and ground state wavefunction of Pr 3+ have been determined. The Ising anisotropic nature of 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.

Single crystal growth, structure and magnetic properties of Pr2Hf2O7pyrochlore

“…The smaller lattice parameter observed in the single crystals may be attributed to a very small difference in the stoichiometry of polycrystalline and single crystalline samples. We note, however, that we could not find evidence for different physical behaviour in powder and single crystal samples, which appears consistent with the good agreement between our heat capacity data taken on single crystal samples [57] and other data recently reported for powder samples [58]. …”

Optimization of single crystal growth of candidate quantum spin-ice Pr2Hf2O7

“…The crystallographic and refinement quality parameters are listed in Table I. The lattice parameters agree very well with that of the polycrystalline Pr 2 Hf 2 O 7 [15,22]. No Pr/Hf site mixing and/or oxygen deficiency could be detected in our refinement, which if present, is expected to be less than 0.5%.…”

“…The fit of C p (T ) data by Debye and Einstein models of heat capacity as detailed in Ref. 26 plus crystal field contribution deduced from the inelastic neutron scattering (INS) measurement on Pr 2 Hf 2 O 7 [15] is shown by the solid red curve in Fig. 6.…”

“…Pr 2 Hf 2 O 7 was found to show no longrange magnetic ordering down to 90 mK, however the frequency dependent behavior of ac magnetic susceptibility clearly reflects slow spin dynamics and spin-freezing behavior [15,16]. While the magnetic ground state of Pr 2 Hf 2 O 7 is Ising anisotropic in nature, the presence of a weak non-Ising contribution is also inferred from the isothermal magnetization data [15] thus favoring dynamic spin-ice behavior in Pr 2 Hf 2 O 7 . Further, Pr 2 Hf 2 O 7 has a non-Kramers doublet ground state which is considered favorable for the dynamic spin-ice behavior [17].…”

“…In our efforts to extend work on rare earth pyrochlores, we recently started working on hafnate pyrochlores [13][14][15] which remained poorly investigated. Our investigations revealed a long-range antiferromagnetic ordering in Nd 2 Hf 2 O 7 (T N ≈ 0.55 K) with an all-in/allout arrangement of Nd 3+ moments determined by the neutron diffraction study [13].…”