Crystal-Field Effects in CoCl2·6H2O

Abstract

The heat capacities of Co${\mathrm{Cl}}_{2}$\ifmmode\cdot\else\textperiodcentered\fi{}6${\mathrm{H}}_{2}$O and Ni${\mathrm{Cl}}_{2}$\ifmmode\cdot\else\textperiodcentered\fi{}6${\mathrm{H}}_{2}$O have been measured between 13 and 200\ifmmode^\circ\else\textdegree\fi{}K. The heat capacity of the Co${\mathrm{Cl}}_{2}$\ifmmode\cdot\else\textperiodcentered\fi{}6${\mathrm{H}}_{2}$O lattice has been estimated from the data on the ${\mathrm{Ni}}^{++}$ salt using a corresponding-states argument and subtracted from the measured total. The remainder is a Schottky anomaly due to the presence of excited Kramers doublets within several hundred ${\mathrm{cm}}^{\ensuremath{-}1}$ of the lowest one. The doublet separations and $g$ factors of the ${\mathrm{Co}}^{++}$ ion in a crystalline field containing cubic, tetragonal, and rhombic components have been computed as functions of the field parameters and spin-orbit coupling constant. A consistent interpretation of the thermal data and the principal values of the $g$ tensor (${g}_{1}=2.23$, ${g}_{2}=5.13$, ${g}_{3}=4.90$) deduced from susceptibility measurements is found to require that the crystalline field contain substantial tetragonal and rhombic components. There is an indication that the spin-orbit coupling constant is smaller than the free-ion value.