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Crystal-field studies of magnetic susceptibility, hyperfine, and specific heat properties of a Ho 2 Ti 2 <mml:mi …

2000; American Physical Society; Volume: 61; Issue: 14 Linguagem: Inglês

10.1103/physrevb.61.9657

1095-3795

Yatramohan Jana, D. Ghosh,

Multiferroics and related materials

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 ${B}_{20}=\ensuremath{-}980,$ ${B}_{40}=1640,$ ${B}_{43}=\ensuremath{-}1800,$ ${B}_{60}=\ensuremath{-}1000,$ ${B}_{63}=700,$ ${B}_{66}=\ensuremath{-}500$ (all in ${\mathrm{cm}}^{\ensuremath{-}1}).$ The separation (\ensuremath{\Delta}) between the lowest non-Kramers' CF doublet and the first excited level was found to be \ensuremath{\sim} 150 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, 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 \ensuremath{\Delta} is small (\ensuremath{\sim} 12 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$). 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 \ensuremath{\sim}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 $12.2\ifmmode\pm\else\textpm\fi{}0.4{\mathrm{K}}^{2}.$ The magnetic energy gains associated with the antiferromagnetic ordering at 1.35 K and that due to Heisenberg exchange interactions $(J\ensuremath{\sim}1\mathrm{K})$ 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.