Gronemann, J.; Chattopadhyay, S.; Gottschall, T.; Osmic, E.; Islam, A.T.M.N.; Anand, V.K.; Lake, B.; Kaneko, H.; Suzuki, H.; Wosnitza, J.; Herrmannsdörfer, T.: Impact of hyperfine contributions on the ground state of spin-ice compounds. Physical Review B 108 (2023), p. 214412/1-8
10.1103/physrevb.108.214412
Open Access Version
Abstract:
We examined the magnetic ground state of the pyrochlore spin-ice compounds Pr2Hf2O7 and Ho2Ti2O7 by means of specific-heat, magnetization, and ac-susceptibility measurements in the mK regime. At these low temperatures, we observe an unexpected large specific heat and corresponding entropy, which diminish in applied magnetic fields. This evidences the presence of additional states beyond the electronic spin and orbital degrees of freedom. We can qualitatively explain the large specific heat by the coupling of the nuclear spins of 141Pr and 165Ho with their electronic counterparts, which leads to a complex hyperfine-coupled term scheme. With increasing fields, the nuclear and electronic spins decouple leaving only the electronic excitations in the measured temperature window. At intermediate fields, a rather evolved term scheme emerges that may explain the unusual hysteretic magnetization and a remarkable state with a negative magnetization found for Ho2Ti2O7. Our findings bring deep insights to the complex ground state of pyrochlore spin-ice compounds and their low-energy excitations.