Crystal-field studies of magnetic susceptibility, hyperfine, and specific heat properties of aHo2Ti2O7single crystal

Accurate measurement of the magnetic susceptibility of a single crystal and a powder sample of nearly cubic pyrochlore ${\mathrm{Ho}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ (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 ${\mathrm{cm}}^{-1}).\mathrm{}$ The separation (Δ) between the lowest non-Kramers’ CF doublet and the first excited level was found to be ∼ 150 ${\mathrm{cm}}^{\mathrm{-}1}$, which explained reasonably well the absence of giant magnetostriction, the Jahn-Teller effect, and the fall of the Young modulus in a HoT crystal at low temperatures, unlike TbT for which Δ is small (∼ 12 ${\mathrm{cm}}^{\mathrm{-}1}$). It was found that the effective hyperfine magnetic field set up at the ${\mathrm{Ho}}^{3+}$ nucleus is 7.2 MG and the total width of the nuclear ground level is ∼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 $12.2\pm 0.4{\mathrm{K}}^2.$ The magnetic energy gains associated with the antiferromagnetic ordering at 1.35 K and that due to Heisenberg exchange interactions $\left(J\sim 1\mathrm{K}\right)$ 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.