Magnetization studies in the rare-earth orthochromites. V.TbCrO3andPrCrO3

The spontaneous magnetization and principal susceptibilities of the rare-earth orthochromites ${\mathrm{TbCrO}}_{3}$ and ${\mathrm{PrCrO}}_{3}$ are studied in the temperature range $4.2\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}\ensuremath{\le}T\ensuremath{\le}{T}_{N}$. For the case of ${\mathrm{PrCrO}}_{3}$ the field dependence of the magnetization at $T=4.2$\ifmmode^\circ\else\textdegree\fi{}K is also measured. For both materials, it is found that (a) the ${\mathrm{Cr}}^{3+}$ spin system orders in a ${\ensuremath{\Gamma}}_{2} ({F}_{x})$ mode, (b) no spin reorientation or compensation point occurs in the observed temperature range, and (c) the effective $g$ tensor of the rare-earth electrons is essentially zero along the $c$ crystallographic axis. The experimental data are interpreted using a doublet model for the rare-earth ion. For ${\mathrm{TbCrO}}_{3}$, ${T}_{N}=167$\ifmmode^\circ\else\textdegree\fi{}K, ${g}_{a}={g}_{b}=12.6$, the effective field exerted by the ordered ${\mathrm{Cr}}^{3+}$ spin system on a ${\mathrm{Tb}}^{3+}$ moment at 0\ifmmode^\circ\else\textdegree\fi{}K is equivalent to a splitting of ${\ensuremath{\Delta}}_{0}=1.8$\ifmmode^\circ\else\textdegree\fi{}K and the crystal-field splitting $D=14$\ifmmode^\circ\else\textdegree\fi{}K. The canting angle $\ensuremath{\alpha}$ of the Cr sublattice is unusally small (less than 5 mrad). For ${\mathrm{PrCrO}}_{3}$, ${T}_{N}=237$\ifmmode^\circ\else\textdegree\fi{}K, ${g}_{a}=2.9$, ${g}_{b}=3.3$, ${\ensuremath{\Delta}}_{0}=17$\ifmmode^\circ\else\textdegree\fi{}K, $D=55$\ifmmode^\circ\else\textdegree\fi{}K, and $\ensuremath{\alpha}=\ensuremath{-}18$ mrad. The negative sign reflects the antiparallel alignment of the Cr and Pr contributions to the spontaneous magnetization.