Crystal-field studies of magnetic susceptibility, hyperfine, and specific heat properties of a Ho2Ti2O7 single crystal

Accurate measurement of the magnetic susceptibility of a single crystal and a powder sample of nearly cubic pyrochlore Ho2Ti2O7 (HoT) were performed between 300 and 70 K. A crystal field (CF) of D-3d symmetry was considered to analyze the results of magnetic susceptibility, magnetization, and magnetostriction studies quite consistently. The best fitted CF parameters were: found as B-20 = -980, B-40 = 1640, B-43 = -1800, B-60 = - 1000, B-63 = 700. B-66 = -500 (all in cm(-1)). The separation (Delta) between the lowest non-Kramers' CF doublet and the first excited level was found to be similar to 150 cm(-1), which explained reasonably well the absence of giant magnetostriction, thr Jahn-Teller effect, and the fall of the Young modulus in a HoT crystal at low temperatures, unlike TbT for which Delta is small (similar to 12 cm(-1)). It was found that the effective hyperfine magnetic field set up at the Ho3+ nucleus is 7.2 MG and the total width of the nuclear ground level is similar to 2 K. The calculated hyperfine and Schottky components of specific heat showed a maximum at 0.3 and 130 K, respectively. The heat-capacity contributions from dipolar interactions in the limit of high temperatures was found to be 12.2 +/- 0.4 K-2. The magnetic energy gains associated with the antiferromagnetic ordering at 1.35 K and that due to Heisenberg exchange interactions (J similar to 1 K) were calculated and found to be 4.82 and 1.5 K, respectively. Specific-heat C-T studies of HoT at low temperatures are suggested.